SC vs. HEMI - Let the TRASH talk begin!

[Yoinkers]

Ok, Ok, i know this is not one of those forums were people get flamed for asking a dumb question, and the atmosphere around here is all very friendly and educational. And thank god for that. So forgive my thread title. I was trying to get attention.

I dont know who really knows who around here so we may all be strangers, i know JL and Snarf hang out, and gbaumann and JL live near one another and all the jeeps have different gear and gearing.

Here is what Im getting to.... Black Betty, Vs. Cherry Bomb (did that name stick? I liked it) gbaumann's hemi. Maybe the turbo makes an appearance.

Not so much a pissing contest, but the actual facts of what we think would happen if we raced them..... And maybe provoke these two guys to find a stretch of pavement to answer all the questions.

[Yoinkers]

FIRST - Power / Weight ratios

Both jeeps make over 300 whp. Understood. Given. Both are rockets. Maybe they will both make a about 330, (bb's chart is around here somewhere)

My point, The SC makes that much power, but the HEMI has to make it earlier in the power band. BUT then we have to factor weight. Is 400 lbs extra weight enough to neutralize the extra early power?

So in a test tube, with everything else excluded, how much does the HEMI's weight hold it back?, Or the SC's weight make up for its steeper power band?

[UselessPickles]

The 6.4 Hemi is the setup that we have the least info about: I have not yet seen a dyno chart of a 6.4 Hemi Wrangler.

However, I did find a dyno chart of a 5.7 Hemi Wranger, and it shows about 27% drivetrain loss compared to the crank power ratings: http://www.jk-forum.com/forums/jk-show-tell-33/5-7l-hemi-dyno-results-89983/#b

click for full size (http://www.jk-forum.com/forums/attachment.php?attachmentid=25499&d=1244913655)
http://www.jk-forum.com/forums/attachment.php?attachmentid=25499&d=1244913655


It's also easy to find dyno charts of 6.4 Challenger SRTs:

click for full size (http://marylandspeed.com/images/charger_2.jpg)
http://marylandspeed.com/images/charger_2.jpg


If we make a big (but reasonable) assumption that the 6.4 Hemi Wrangler will also have about 27% drivetrain loss also, it's easy to take that 6.4 Hemi torque curve and scale it down accordingly. This is really the best estimate we could possibly come up with for the torque at the wheels of a 6.4 Hemi Wrangler right now.


So I've also taken data from JeepLab's dyno charts for stock, RIPP and Magnuson. I got torque curve data for the Prodigy turbo from Prodigy's dyno charts. Here they are all together in one chart for comparison:

click for full size (http://www.uselesspickles.com/files/jeep/torque_stock_mag_ripp_prod_hemi.png)
http://www.uselesspickles.com/files/jeep/torque_stock_mag_ripp_prod_hemi.png


The 6.4 Hemi definitely has the all-around nicest torque curve. In the upper RPMs, the turbo has a significant advantage, even before taking into consideration the extra 400 lbs of the Hemi.


UPDATE: Here's a power chart, for those that like to think in terms of power rather than torque.

click for full size (http://www.uselesspickles.com/files/jeep/power_stock_mag_ripp_prod_hemi.png)
http://www.uselesspickles.com/files/jeep/power_stock_mag_ripp_prod_hemi.png

[2k13jk]

Ripp did a dyno pass with a 392 in awd and make 325 wheel

[Gunner]

https://www.youtube.com/watch?v=p1A64GjXe6o

[UselessPickles]

So what does this all mean for what really matters: acceleration?

Luckily, I've written some code to process torque curve data, along with other key specs about a vehicle (weight, gear ratios, tire size, aerodynamic drag, etc.) and simulate how they would accelerate under full throttle.

For all my acceleration simulations, I assume the following (based mostly on my Jeep):

Base model 2-door Wrangler with 3.21 axles and stock 29" tires.
Weight for 6.4 Hemi: 4249 lbs = 3849 lbs (base model curb weight) + 400 lbs (AEV's claim of added weight)
Weight for all others: 3960 lbs (my actual weight (http://jeeplab.com/showthread.php?131-Prodigy-Performance-3-6-Turbo-DIY-Install&p=4781&viewfull=1#post4781); assuming all bolt-on kits are close enough in weight to not have a big impact on results)
Weight of driver: 140 lbs (my weight)
Stock 6-speed manual transmission. THIS IS NOT CORRECT FOR THE HEMI. Unfortunately, my code can only simulate a manual transmission. This is the best I can do for this comparison. It's still at least an interesting comparison of the differences in torque curves (and weight), with ALL ELSE being equal.
For simulated races, launch at 2500 rpms, perfectly slipping the clutch (holding 2500 rpm during the entire launch) at full throttle, and executing gear changes in 0.6s each.
11 inches of "roll-out" before the race officially begins for the 1/4 mile races. This simulates how cars are "staged" for a drag race, and how they trigger the timing system to start.


NOTE: I'm not claiming that my simulation will perfectly simulate the real world and make perfect predictions. Real world results depend on so many variable factors, human imperfection, etc. The goal of the simulation is not to accurately predict real-world results, but to compare relative real-world *potential* between different vehicles/configurations, using computerized perfection to remove the uncontrollable variables of the real world. This allows us to objectively/relatively compare stuff without arguing about whether the results were simply due to difference in driver skill, a bad launch, a poorly timed shift, bad weather conditions for traction, etc.


Now on to some fun results...

First up is a chart showing for any given road speed, what is the fastest the Jeep could accelerate at that speed if you're in the best transmission gear for max acceleration. Due to the torque curve shapes, the best gear for acceleration in this case is always the lowest gear you can possibly be in at that speed (upshift as close to the rev limiter as you can), but this is not true of all vehicles/engines.

click for full size (http://www.uselesspickles.com/files/jeep/acceleration_stock_mag_ripp_prod_hemi.png)
http://www.uselesspickles.com/files/jeep/acceleration_stock_mag_ripp_prod_hemi.png


Where the end of each line hits the bottom of the chart (0 acceleration) represents the predicted top speed.

That's interesting data, but it doesn't really clearly show how quickly each Jeep will be able to accelerate up to speed over time. For that, I can simulate a 1/4 mile drag race for each and graph speed vs time:

click for full size (http://www.uselesspickles.com/files/jeep/drag_race_speed_stock_mag_ripp_prod_hemi.png)
http://www.uselesspickles.com/files/jeep/drag_race_speed_stock_mag_ripp_prod_hemi.png


The end of each line indicates the time and speed at which the Jeep passes the finish line. Here's the numeric results:

Stock:
15.89s @ 85.79 mph

Magnuson:
14.05s @ 97.87 mph

RIPP:
13.89s @ 98.05 mph

6.4 Hemi:
13.27s @ 101.53 mph

Prodigy:
13.18s @ 106.62 mph


Another interesting aspect is how quickly does each Jeep actually move down the track? The most interesting and clearest way of presenting this that I found was to show how much of a lead each modded Jeep has over a stock Jeep throughout the race. This gives a pretty good visual of how much they all leave the stock Jeep in the dust, and also how they "jockey for position" with each other throughout the race:

click for full size (http://www.uselesspickles.com/files/jeep/drag_race_lead_stock_mag_ripp_prod_hemi.png)
http://www.uselesspickles.com/files/jeep/drag_race_lead_stock_mag_ripp_prod_hemi.png


I think this is the best visualization of how the different power mods actually compare to each other in acceleration. The 6.4 Hemi clearly destroys both superchargers. The turbo clearly has an early disadvantage due to its minimal low RPM gains, but more than makes up for it by the end with his upper RPM power.

Keep in mind, though, that this is a race from a complete stop to a 1/4 mile distance. Not quite a typical real-world scenario. For example, cross-reference the two drag race charts to compare how each Jeep would perform when accelerating up to various legal road speeds. You may find that one Jeep (Prodigy) will reach a target speed in a shorter amount of time, but a different Jeep (6.4 Hemi) is actually further ahead by distance, despite requiring more time to get up to speed.

Also keep in mind that a 2500 rpm launch was arbitrarily chosen because it seems reasonable and minimally abusive to the clutch. Launching at higher rpms would produce very different results for the turbo, while having relatively limited impact on the results of all the other Jeeps, but is not a very good representation of how you would most likely drive it on the streets.

On the other hand, if you begin the acceleration from a rolling start at some higher speed, like executing a pass on a highway for example, differences in low end torque won't matter because you can downshift for maximum acceleration (see the first chart in this post).

The actual results of any "race" between these different Jeeps will vary quite a bit depending on the starting speed, and whether it is a race to a particular speed, a race to see who covers a given amount of distance first, or a race to see who is furthest ahead after a given amount of time.


I think it is safe to say, though, that the 6.4 Hemi should be a rocket with the best balance of torque/acceleration available at any time.


(if you want to skip past a couple pages of bickering and see more analysis, click here (http://jeeplab.com/showthread.php?251-SC-vs-HEMI-Let-the-TRASH-talk-begin!&p=4841&viewfull=1#post4841))

[UselessPickles]

Ripp did a dyno pass with a 392 in awd and make 325 wheel

That was, unfortunately, in 4HI because of some technical issue about the traction/stability control systems not allowing a rear-wheel-only dyno run.

My 27% drivetrain loss assumption gives about 345 hp and 350 ft-lbs of torque at the rear wheels for the 6.4 Hemi. This seems like a reasonable difference between 4WD and RWD numbers. Maybe? No idea, actually :)

[UselessPickles]

Here's simulated 0-60 mph times...

Stock:
7.59s

Magnuson:
5.49s

RIPP:
5.36s

6.4 Hemi:
4.62s

Prodigy:
4.81s

[Timmy]

Here's simulated 0-60 mph times...

Stock:
7.59s

Magnuson:
5.49s

RIPP:
5.36s

6.4 Hemi:
4.62s

Prodigy:
4.81s

I would love to see your 0-60 time Pickles and compare it to your calculations. 4.81s is just insane! Part of me is sitting here thinking, no way on earth are you going to see that, then the other part says, well... maybe so. I really would be shocked if you are below 5 seconds. An Audi S4 has a 0-60 of 5.2 seconds. That's a 6cyl with a supercharger on it producing 333hp that is geared for speed, weighs 3985 lbs (close to your weight) and has a drag coefficient of 0.30 compared to a Jeep somewhere north of 0.50 (stock.)

Drag Coefficient Comparison
Passenger Train 1.80
Ski jumper 1.20 - 1.30
Person (upright position) 1.00 - 1.30
Old Car like a T-ford 0.70 - 0.90
Tractor Trailer 0.96
Bike racing 0.88
JEEP Wrangler Modified 0.82 (stubby bumper, flat fenders, big-A tires ;-)
Brick Cube 0.80
JEEP Wrangler Stock 0.58 (stock)
Solid Hemisphere 0.42
Bird 0.40
Audi S4 0.30
Common Car like Open Vectra (class C) 0.29
Supersonic Fighter 0.016
Subsonic Transport Aircraft 0.012

[KaiserBill]

Ok, Ok, i know this is not one of those forums were people get flamed for asking a dumb question, and the atmosphere around here is all very friendly and educational. And thank god for that. So forgive my thread title. I was trying to get attention.

I dont know who really knows who around here so we may all be strangers, i know JL and Snarf hang out, and gbaumann and JL live near one another and all the jeeps have different gear and gearing.

Here is what Im getting to.... Black Betty, Vs. Cherry Bomb (did that name stick? I liked it) gbaumann's hemi. Maybe the turbo makes an appearance.

Not so much a pissing contest, but the actual facts of what we think would happen if we raced them..... And maybe provoke these two guys to find a stretch of pavement to answer all the questions.

If you really want decent data you have to some serious technology on the truck for data recording and you have to have a controlled environment like a race track.

However, isn't the point of a Jeep to go off road? So shouldn't the test be something more off road associated?


https://www.youtube.com/watch?v=-VkctMEQUgM

This is what I would try to do-- put the trucks into a real off road conditions!

[gbaumann]

My 27% drivetrain loss assumption

Pickles. Is power loss in the drivetrain always a percentage of engine hp/torque that scales with the engine or does it take a fixed amount of effort to turn the drivetrain at a given rpm/gear? In other words would a 1000 hp engine give up 250 hp to turn the driveline based on a 25% loss factor; a 500/125; 100/25 and so on or do all engines start with a -X loss due to the hp/torque required to turn the drivetrain?

[KaiserBill]

Pickles. Is power loss in the drivetrain always a percentage of engine hp/torque that scales with the engine or does it take a fixed amount of effort to turn the drivetrain at a given rpm/gear? In other words would a 1000 hp engine give up 250 hp to turn the driveline based on a 25% loss factor; a 500/125; 100/25 and so on or do all engines start with a -X loss due to the hp/torque required to turn the drivetrain?

All depends on the efficiency of the transmission, differentials, number of axles being driven. 27% seems a little high to me. I've had my truck dynoed when I first bought it-- it has about 140hp at the flywheel at 2600 rpm and it showed about 120-125hp at 2600rpm redlined at the rear wheels or about 14.29% loss. Which is pretty good.

[gbaumann]

Let's get all four power mods to the dyno for JeepLap Spring Dyno Day 2015. Then get them on the trail! As much as I'm dying to see the numbers I'm also looking forward to meeting some of you guys and getting a day out in the woods.

Comparing the SC Pentastar to the 6.4L hemi is easy for me in certain respects. I ran the Mag unit for almost 25,000 miles. It was a struggle to say the least due to the auto trans issues. But, of course, I know what forced induction does for the Pentastar because I could manually make conditions right and get her on boost when I wanted. I'm now driving the same truck with the 6.4L. So I'm experiencing it in real time. I'm not sure how to describe the difference. Every time I get in the truck convinced that I'm going to really study the differences I step on the gas and the logic center in my brain dumps all operations. The only result I get as output is a juvenile giggle that keeps looping until I turn the truck off.

[UselessPickles]

I would love to see your 0-60 time Pickles and compare it to your calculations. 4.81s is just insane!

I will refer you to this statement in my previous post :)



NOTE: I'm not claiming that my simulation will perfectly simulate the real world and make perfect predictions. Real world results depend on so many variable factors, human imperfection, etc. The goal of the simulation is not to accurately predict real-world results, but to compare relative real-world *potential* between different vehicles/configurations, using computerized perfection to remove the uncontrollable variables of the real world. This allows us to objectively/relatively compare stuff without arguing about whether the results were simply due to difference in driver skill, a bad launch, a poorly timed shift, bad weather conditions for traction, etc.

However, I do purposely use input (launch rpm, gear shift time) that seems reasonably attainable to get results that are reasonably close to what should be possibly in the real world. I definitely need to improve my launching skills before I can hope to approach the predicted results :)



Part of me is sitting here thinking, no way on earth are you going to see that, then the other part says, well... maybe so. I really would be shocked if you are below 5 seconds. An Audi S4 has a 0-60 of 5.2 seconds. That's a 6cyl with a supercharger on it producing 333hp that is geared for speed, weighs 3985 lbs (close to your weight) and has a drag coefficient of 0.30 compared to a Jeep somewhere north of 0.50 (stock.)

A couple things...

* Drag coefficient is not the full story of the vehicle's aerodynamic drag. A drag coefficient (Cd) only describes the shape, but not the size. The drag coefficient must be multiplied by the frontal area to get the drag-area coefficient (CdA), which is what is actually used in calculations to determine the force of aerodynamic drag. So the Wrangler has even a bigger disadvantage than you would expect from drag coefficients alone (compared to typical cars) due to its larger frontal area.

* Aerodynamic drag doesn't have a very big impact on 0-60 mph times. To illustrate this, I simulated the turbo Wrangler's 0-60 run as if it had the same aerodynamic drag as a 2006 WRX STi. The STi's CdA value I have is 0.694. That's less than half of the Wrangler's CdA of 1.762. The end result for a turbo Wrangler that is more than twice as aerodynamic than reality is 0-60 mph in 4.78s. That's only 0.03s faster. Power:weight ratio has a much larger impact on 0-60 times than aerodynamics, just because so much of the 0-60 mph run is spent at low speeds where aerodynamic drag is minimal.

* My Wrangler is almost exactly the same weight as the Audi S4 example, but with about 380 whp, compared to the S4's 333 whp. Given that power:weight ratio is the dominant factor in 0-60 mph times, the turbo Wrangler's simulated 4.81s vs the S4's 5.2s seems pretty reasonable.

[UselessPickles]

Pickles. Is power loss in the drivetrain always a percentage of engine hp/torque that scales with the engine or does it take a fixed amount of effort to turn the drivetrain at a given rpm/gear?

Both :)

My brother (grad student in physics) and I actually explored this question (and many others) by working through the relationships between things from the engine, through the drivetrain, all gear reductions, through the tires, to the dyno drum, as a complete system being accelerated in a power pull sweep on a dynojet style dyno. I'll spare you the math and try to just describe the findings relevant to your question.

The context of what I say here is limited to a vehicle on a dynojet style dyno, going through an rpm sweep power pull with a given transmission gear, axle ratio and tire size. Things change as you change transmission gear, axle ratios and tire size. I do not attempt to cover this here.

There's two main components to drivetrain loss:
1) Loss due to friction.
2) loss due to moment of inertia of all the drivetrain components.

For a given drivetrain, transmission gear, axle ratio, etc., the amount of the engine's torque that is "consumed" by friction is practically constant. Doesn't matter how fast the drivetrain is spinning or how quickly it is accelerating. So this component takes a "fixed amount of effort" as you worded it.

The loss due to moment of inertia is directly proportional to how quickly the drivetrain is being accelerated. On a dyno (at least, on a dynojet dyno in a power pull sweep), the drivetrain is accelerated at a rate directly proportional to the amount of torque the engine produces (minus the the amount of torque required to overcome drivetrain friction). This component is essentially a "percentage of the engine hp/torque".

Due to the way dyno power pulls are done (on Dynojet and similar dynos, at least) with a fast sweep through the RPM range (quick acceleration) with a fixed dyno drum mass, the loss due to moment of inertia is much more significant than loss due to friction. So for a given drivetrain, the amount of drivetrain loss will be close to the same percentage, but that percentage of loss will go down some as you increase the engine's power because there is the friction component of the loss that is constant. That frictional loss becomes a smaller percentage of the engine's total output as you increase the engine's output. The specifics of how much the overall percentage will change depends on the specifics of the particular vehicle's drivetrain friction and moment of inertia.

There's lots more details I could try to get into about what/how a dyno technically measures, differences between different types of dynos, etc., but I think what I've said so far is good enough for the context of this discussion (measured drivetrain loss on a dynojet dyno).

One interesting note worth mentioning, though, is that a steady dyno pull (where the dyno applies torque to hold the RPMs steady, records the amount of torque, moves up to another RPM, rinse and repeat) completely removes the drivetrain's moment of inertia loss from teh equation because the drivetrain is not accelerating while taking the measurement. This would result in higher dyno number, and a completely constant amount (not percentage) of drivetrain loss, because friction is now the only source of loss. This does not produce realistic results, though, because most people want dyno results to gain an understanding of how the vehicle will accelerate... not how much work it can do at a steady speed.



27% seems a little high to me. I've had my truck dynoed when I first bought it-- it has about 140hp at the flywheel at 2600 rpm and it showed about 120-125hp at 2600rpm redlined at the rear wheels or about 14.29% loss. Which is pretty good.

Your truck is not a Wrangler. Stock Wranglers typically show about 30-33% drivetrain loss. JeepLab's dyno results for the stock Wrangler show a 33% loss. So 27% loss with the Hemi is not unreasonable. Since the 27% loss came from a 5.7 Hemi dyno chart, I actually expect that the 6.4's drivetrain loss will be a bit less than 27% (see above explanations), but nowhere near something like your truck's 14%.

Also keep in mind that there's a difference in transmission with the Hemi Wranglers, so that could be a significant factor in the difference in drivetrain loss between stock and 5.7 Hemi.

Basically, like I said at the beginning, we don't have any exact data fro the 6.4 Hemi Wrangler, so I'm just doing the best I can with the data I can find to create a close approximation. Don't take the exact simulated numbers/times as absolute truth. Just look at overall general trends as an approximated relative comparison.

[KaiserBill]

If you haven't actually removed your engine to dyno to figure out bhp then you really cannot tell how much you've lost due to the drivetrain. It is all guess work.

[UselessPickles]

It's reasonable estimation based on known drivetrain loss of a 5.7 Hemi Wrangler, comparing dyno charts to crank hp ratings. Again, read all the things I already stated about this being a best estimate with the available data, to be used for comparing general trends and relative differences. More specifically, for comparing large relative differences. Any area where the differences are very small could be well withing a margin of error of the assumptions.

The data I have so far is enough to see that the 6.4 Hemi will clearly destroy the superchargers throughout the RPM range, will destroy the turbo at low RPMs, but the turbo will likely have some level of advantage in the upper RPM range.

I'll gladly update everything as soon as someone produces an actual dyno chart of a 6.4 Hemi Wrangler. The amount of drivetrain loss becomes irrelevant then, because we'll have an actual measured torque curve at the wheels.

[HahaJK]

Looking at this from the view of a guy that wants more power for primarily trail runs and the occasional rock crawl, prodigy seems to be the best answer dollar for dollar. The 6.4L is out of the question simply due to price, but Magnuson, RiPP and Prodigy are all in the same ball park.

Reading up on the hot side of the turbos and pipes as well as the future problems of the prodigy though, I'm more swayed towards RIPP with a high boost pulley.

[gbaumann]

Pickles, the 6.4L and 5.7L hemis since 2012 use the original trans. I have the same WA580E/NAG-1 that was bolted to my Pentastar. So your assumptions should be pretty good if you're figuring in the original trans dynamics.

[gbaumann]

I know we're focused here on power but if Pickles has any spare computing time can we get a chart showing where the dollars go for these mods as they relate to power? We know what Mag, Ripp and Prodigy cost. I spent $28k on the 6.4. Which of the FI kits puts the torque/dollar in the most efficient spot? I'm assuming there's nothing efficient about the cost of the hemi. Assume daily driving with a typical commute and weekend trail time.

[KaiserBill]

It's reasonable estimation based on known drivetrain loss of a 5.7 Hemi Wrangler, comparing dyno charts to crank hp ratings. Again, read all the things I already stated about this being a best estimate with the available data, to be used for comparing general trends and relative differences. More specifically, for comparing large relative differences. Any area where the differences are very small could be well withing a margin of error of the assumptions.

The data I have so far is enough to see that the 6.4 Hemi will clearly destroy the superchargers throughout the RPM range, will destroy the turbo at low RPMs, but the turbo will likely have some level of advantage in the upper RPM range.

I'll gladly update everything as soon as someone produces an actual dyno chart of a 6.4 Hemi Wrangler. The amount of drivetrain loss becomes irrelevant then, because we'll have an actual measured torque curve at the wheels.


I read your statements. You're once again making too many assumptions based on too little data. You've derived this figure of 30-33% loss due to drive train without actually having any really good baseline information about the Pentastar Engine that I can see. You're seeing Wheel HP figures and attempting to working backwards to a Flywheel/Brake HP figure without having enough data about the engine. I've not seen one add on kit that talks about BHP and not WHP... In fact all of them state the fact that they only test on chassis dynos.. Which sort of makes me wonder what they are trying to fudge with the for marketing purposes. People will say "Oh Wow... It is has to be so much more at the flywheel..." and purchase this kit. And they don't take the engines out and really dyno them.

If you want to really find out how much your engine is loosing between transmission, transfer case, axles and so on you have to take the engine out and dyno it and find out what sort of power you're getting. And then if you want to talk about Jeeps in general you have to get a very respectable sampling size of all the possible combinations from the factory so you can say okay -- Engines alone had this tolerance in power +/- over the stated horsepower, then hook it up to the transmission and dyno that combination and that will give you the ability to see what the power loss is in that combination, then you can check out the axle ratio combinations. Then you can build a baseline and come up with same average performance numbers and say okay-- this what A JKU with 3.6L V6 and 6spd Manual with 4.10's averages out to or model x , z, y... and then you say okay lets play with this variable or that one. Right now all your data is vehicle specific and it is way too general to even make any meaningful conclusions about performance extending past a few controlled variables.

For example if this AEV kit makes 400Hp at it sees a 27% loss in power it is down to 292WHP ... I'm skeptical that you will see the types of losses you claim the wrangler is seeing. For example if the Ripp system creates 325 hp at the rear wheels and that is after it has lost a 1/3 of it's power that means it must have well over 400hp at the crankshaft! They want you to believe that you making what nearly 200hp extra at the crankshaft with a bolt on turbo kit and not affecting the compression ratio and so on. I could see a 125-136hp at the crank shaft and loss of about 30-40hp through the drive train at best.

I think you've done a lot of hard work but the problem is you need more data still to make any really interesting conclusions beyond that of your vehicle.

[KaiserBill]

The next person to do a V8 conversion should look into NRE-- they are the real deal. A NA 454cid engine that makes 625hp and 580ft-lbs of torque on Pump gas is pretty amazing for a daily driver engine.

http://www.nelsonracingengines.com/pricesheets/chevy/dailydriver/na/dds_454bbc_na.pdf

[UselessPickles]

I have not discussed at any point or attempted the idea of calculating bhp for any of the mods. Torque at the wheel is what matters, is what the dyno charts provide, and is what I use.

We know the SAE ratings for bhp for the stock engines. Pentastar is 285 bhp. JeepLabs stock dyno shows 190 whp. That's a 33% loss from bhp to whp. If the SAE rating is not a solid enough baseline bhp for you, then that's not my problem.

Again, all this talk of drivetrain loss was just to get an estimation of torque at the wheels for the 6.4 Hemi Wrangler in the absence of a dyno chart for this vehicle, to get some better estimations of how it performs compared to the superchargers rather than pure speculation based on hunches. Take it for what it is, ignore it if you think it's garbage, I really don't care. I hope we can get a dyno chart soon so I can update my model of the 6.4 Hemi Wrangler with actual measured torque at the wheels.

[FLIPmeOVER]

Here's simulated 0-60 mph times...

Stock:
7.59s

Magnuson:
5.49s

RIPP:
5.36s

6.4 Hemi:
4.62s

Prodigy:
4.81s

Keep in mind, these numbers are with 3.21 geared 2 door wranglers. (probably).

Stripped down to bare bones.

real jeeps dont do those times.

Pickles turbo might. Thats a soft top 2 door right? What do you say pickles, can you do a 4.8 0-60?

[UselessPickles]

Keep in mind, these numbers are with 3.21 geared 2 door wranglers. (probably).

Stripped down to bare bones.

real jeeps dont do those times.

Pickles turbo might. Thats a soft top 2 door right? What do you say pickles, can you do a 4.8 0-60?

Yes, if you read one of my first posts in this thread, I lay out the exact conditions/assumptions. I based it on my Jeep (base model 2-door sport, manual trans, soft top, 3.21 gears, stock 29" tires, etc). I wouldn't say it's "stripped down", because I haven't removed anything. I'm even using a vehicle weight that includes a full tank of gas.

I also pointed out that it's not the exact numbers/times/results that are important here, but the relative differences. It gives a good indication of how each power mod performs compared to each other, all else being exactly equal (a comparison that is not likely to ever happen in the real world because of the huge variety in vehicle configurations for Jeeps).

I could re-run all the simulations with heavier Jeeps with bigger tires and different axle gearing, but that's a lot of work and I'm lazy :-p
I used the configuration of my Jeep because... well, that's how my Jeep is, so that's what I'm most interested in. I may be self-centered, but at least I'm sharing my findings :)

I'll take my Jeep to a drag strip this summer to see how close I can get to the 0-60 mph and 1/4 mile predictions from my simulation.

BTW - You hurt my Jeep's feelings by implying it's not a "real" Jeep. It gets around off road just fine for my purposes:


http://www.uselesspickles.com/files/jeep/driving_up_sand_dune.jpg



https://www.youtube.com/watch?v=LOkcGb7Q9A0

[KaiserBill]

SAE rating is not written in stone. SAE is just a set of standards for measuring-- those measurements will still have a tolerance. You're jeep is built to SAE standard inch pattern tolerances and guess what not every Jeep is exactly the same. So, your point shows me you've never worked with any manufacturing process otherwise you would know just as I do that advertised power or torque is often less than or greater than what you get out of an engine. Because of various factors found within the manufacturing process.

I don't think what you're doing is garbage. I just think you need to realize that when you take into account all the possible areas for margin of error in the process you will find that 33% drivetrain loss is pretty high. Usually, most studies show less loss than that in a drive train.

[FLIPmeOVER]

Yes, if you read one of my first posts in this thread, I lay out the exact conditions/assumptions. I based it on my Jeep (base model 2-door sport, manual trans, soft top, 3.21 gears, stock 29" tires, etc). I wouldn't say it's "stripped down", because I haven't removed anything. I'm even using a vehicle weight that includes a full tank of gas.

I also pointed out that it's not the exact numbers/times/results that are important here, but the relative differences. It gives a good indication of how each power mod performs compared to each other, all else being exactly equal (a comparison that is not likely to ever happen in the real world because of the huge variety in vehicle configurations for Jeeps).

I could re-run all the simulations with heavier Jeeps with bigger tires and different axle gearing, but that's a lot of work and I'm lazy :-p
I used the configuration of my Jeep because... well, that's how my Jeep is, so that's what I'm most interested in. I may be self-centered, but at least I'm sharing my findings :)

I'll take my Jeep to a drag strip this summer to see how close I can get to the 0-60 mph and 1/4 mile predictions from my simulation.

BTW - You hurt my Jeep's feelings by implying it's not a "real" Jeep. It gets around off road just fine for my purposes:


http://www.uselesspickles.com/files/jeep/driving_up_sand_dune.jpg



https://www.youtube.com/watch?v=LOkcGb7Q9A0

I didnt mean your jeep wasnt a real Jeep. I mean that when the power mod companies give out those numbers, its not an unlimited rubicon they are using.

They are using the lighest possible jeep configuration. Wich almost all of us do not have. Got a hard top? those are not your numbers anymore. Got a 4 door? those are not your numbers anymore. Aggressive gearing? Not your numbers anymore.

Your jeep is plenty real. REAL FAST.

[UselessPickles]

Reading up on the hot side of the turbos and pipes as well as the future problems of the prodigy though, I'm more swayed towards RIPP with a high boost pulley.

Generalizations about hot pipes on turbo systems may not apply to the Prodigy system. The turbo is intentionally over-sized a bit for various reasons, so that it ends up not spooling much during typical cruising conditions. When the turbo is not spooled up and producing much boost, it's also not producing much waste heat beyond what a plain exhaust pipe would already do. If you're concerned about under-hood heat, then get the pipes ceramic coated. Also definitely put a turbo blanket on the hot-side of the turbo. The turbo kit also removes two sources of heat from under the hood: the catalytic converters. A new high-flow catalytic converter is included with the kit, and it's located about under the driver-side seat, underneath the vehicle (not in the engine compartment).

Off-road driving also does not spool up the turbo much in my experience. When I'm off road, I make use of gearing (4LO, low transmission gears) to keep RPMs up a bit in the mid-range area when I'm climbing stuff, which makes use of all the torque multiplication to keep engine load low, and throttle response good. Low engine load means low exhaust flow, which means minimal turbo spooling, and minimal extra heat from the turbo. The turbo itself, the wastegate, and some of the exhaust pipes are conveniently right behind the radiator fans and in airflow for cooling.


What "future problems" are you referring to?



Pickles, the 6.4L and 5.7L hemis since 2012 use the original trans. I have the same WA580E/NAG-1 that was bolted to my Pentastar. So your assumptions should be pretty good if you're figuring in the original trans dynamics.

Unfortunately, that still doesn't help me, because that's the stock automatic transmission. I currently have no way to model the behavior of an automatic, especially the torque multiplication of the torque converter whenever the converter is not locked up (which will especially affect the initial launch). I can only model behavior a manual transmission, so I'm limited to modeling a theoretical 6.4 Hemi with the Jeep's 6-speed manual (is that even a possible combination?). At least it's consistent for comparison to the rest of the power mods, which can definitely coexist with the stock manual transmission.



I know we're focused here on power but if Pickles has any spare computing time can we get a chart showing where the dollars go for these mods as they relate to power? ... Assume daily driving with a typical commute and weekend trail time.

Not quote sure what you're asking for here. Could you be more specific?

I also still plan to make some more charts illustrating how each option can accelerate in more normal driving situations - not in the best transmission gear for max acceleration. This will allow you to compare, for example, how much acceleration potential is there at 50 mph in 5th gear, and how many gears would less powerful options need to downshift to get equivalent acceleration at the same speed. I can already tell you without any doubt that the Hemi will be the indisputable winner here, and will cause the Hemi to generally "feel" much more powerful in daily driving that all other options (including Prodigy), even if Prodigy's turbo actually makes more power and is capable of faster full-throttle acceleration.

[UselessPickles]

You're jeep is built to SAE standard inch pattern tolerances and guess what not every Jeep is exactly the same. So, your point shows me you've never worked with any manufacturing process otherwise you would know just as I do that advertised power or torque is often less than or greater than what you get out of an engine. Because of various factors found within the manufacturing process.

I think you're missing the point of all of this. I am well aware of manufacturing tolerances. The goal here is NOT to perfectly simulate one specific vehicle with its own specific combinations of variations within tolerances. That would be ridiculously complicated.

The goal is to get a general comparison of potential between the different power mods. Just like when comparing dyno charts, it must be taken with a grain of salt with the understanding that there are margins of error. I cannot possibly actually take into account all margins of error in my calculations to produce a "range" of possible results. The best I can do is acknowledge that there are margins of error. I have provided full disclosure on where I got my data, what assumptions were made, etc. It is up to you, the viewer, to take this all into consideration when viewing the results and realize that the results are not perfect, but are at least good enough to identify larger scale differences and trends.



I just think you need to realize that when you take into account all the possible areas for margin of error in the process you will find that 33% drivetrain loss is pretty high

Maybe we're just talking completely different languages. When I say "drivetrain loss", I am specifically referring to what is is commonly called "drivetrain loss" among automotive enthusiasts, which is a representation of the difference between manufacturer claimed crank hp numbers, and whp numbers as measured by a chassis dyno during an dynamic acceleration sweep through the rpm range.

By this definition, you cannot possibly tell me that 33% is not correct for the Wrangler, because that is exactly what multiple sources have found to be the difference between the manufacturer's claimed crank hp for the Pentastar in the Wrangler (285 bhp) and the measured whp on a dyno (~190 whp). 190 is 33% less than 285. This is not debatable.

You may be talking about steady-state drivetrain loss, which is the amount of drivetrain loss while maintaining a steady speed. As I described in an earlier post already, this completely removes the drivetrain lost due to moment of inertia because there is no acceleration occurring. This leads to dyno results that are much higher, and therefore drivetrain loss amounts/percentages that are much lower. However, this is not a realistic result for analyzing how quickly a vehicle might be able to accelerate, because in order to accelerate the vehicle, you must accelerate the drivetrain, which will cause additional drivetrain loss due to moment of inertia of drivetrain components resisting rotational acceleration. Steady-state drivetrain loss is most useful for analyzing a vehicle's steady state cruising efficiency.

[UselessPickles]

BTW - my simulation based on dyno torque curve data has actually proven to produce realistic results for several vehicles already. My favorite example is a 2006 WRX STi. My brother bought one last year and was interested in using my simulation get some idea about how launching at different RPMs and different quickness of shifting gears might affect acceleration performance.

We found a stock dyno chart online, a measured coefficient of drag and frontal area, specs for transmission ratios, weight and tire size. Everything we needed.

First simulated run, launch hard at peak torque, assuming 0.5s shift times, and I got...

0-60mph: 4.9s
1/4 mile: 13.01s @ 104.4mph

One car website reported 4.9s 0-60, but no 1/4 mile time.

Another car website reported 4.5s 0-60, and 13.0 sec @ 103.5

Almost a perfect match to the reported 1/4 mile time, and a perfect match to one of the reported 0-60 mph times. But that quicker 4.5s 0-60 time from the other website was really bothering me. Which one was correct? 4.9 or 4.5? How could there be such a big difference? And what concerned me the most was that the website that had the 1/4 mile result that agreed with my simulation was the source of the 0-60 time that did NOT agree with my simulation! What have I done wrong!?!?!

Then I remembered that some car testers use a 1-foot roll-out (like a 1/4 mile race) for all acceleration-from-a-stop tests, including 0-60 mph tests. This produces quicker 0-60 results because there's a 1-foot head start before the timer starts. So back to the simulation to test this hypothesis...

Simulated 0-60 with 1-foot rollout: 4.57s

Much better!

I was then able to slightly tweak the launch RPMs and shift times, still within a reasonable range, and get results that even more perfectly matched the websites reported results.

[gbaumann]

Pickles. (Friendly trash talk coming) I just have to ask a question on your data. Do you really weigh 140 lbs.? Every time I read through the posts and replies I see all the discussion about this and that data point and assumptions. And I keep saying to myself does anyone else notice he weighs 140lbs.?

On a serious note. When I put Cherry Bomb (getting used to the name) on the dyno should I ask for specific data or output in a specific format/file type for you?

[UselessPickles]

Yes, I really am a 140 lbs, 6-foot tall pole. If I turn sideways, you might not be able to see me :)

When you put your Cherry Bomb on a dyno, try to use a shop that has the same type of Dynojet dyno that JeepLab has already used for stock, RIPP and Magnuson (harass Ross, aka "JeepLab", for details).

Also, ask them to email the dyno run files to you. Not an image of the graph, not a scanned copy of a printout of the graph. The actual raw run file from the dyno software. This file can be viewed with Dynojet's WinPEP 7 Dyno Run Viewer program, which can be found here: https://www.dynojet.com/Downloads/Software-and-manuals.aspx?ProdType=Dyno-Software-Firmware-Other. It lets you zoom around, pick different display options, print out your own graphs, etc.

More importantly, the dyno run viewer program can export the raw data at 100 rpm intervals in a format that I can easily load into my simulation, rather than requiring me to take measurements from an image of the graph.

[gbaumann]

When you put your Cherry Bomb on a dyno, try to use a shop that has the same type of Dynojet dyno that JeepLab has already used for stock, RIPP and Magnuson (harass Ross, aka "JeepLab", for details).

The dyno we're thinking of is here in NJ not far from me and is the same dyno that Sweat Pea went on with the Mag S/C. I'll print your post and press them to release the files in your desired format. Importing is much easier than trying to read from of a crocked scan!

[UselessPickles]

I figured I should also make a power chart to go along with the torque chart. Here's both charts together for your convenience. I also updated my first post in this thread to add the power chart.

click for full size (http://www.uselesspickles.com/files/jeep/power_stock_mag_ripp_prod_hemi.png)
http://www.uselesspickles.com/files/jeep/power_stock_mag_ripp_prod_hemi.png

click for full size (http://www.uselesspickles.com/files/jeep/torque_stock_mag_ripp_prod_hemi.png)
http://www.uselesspickles.com/files/jeep/torque_stock_mag_ripp_prod_hemi.png

[UselessPickles]

Time for some data that can really help you understand how each of these mods might affect more realistic/common daily driving situations. I already showed how each power mod does at maximum acceleration through all the gears. Here's a refresher:

click for full size (http://www.uselesspickles.com/files/jeep/acceleration_stock_mag_ripp_prod_hemi.png)
http://www.uselesspickles.com/files/jeep/acceleration_stock_mag_ripp_prod_hemi.png


That's all well and good, but it's missing the full picture of how each one can accelerate throughout the entirety of 2nd through 6th gears. You probably want to be able to see how much potential acceleration you might have at the ready in 6th gear while driving 70mph to have a good idea of how well you'll be able to manage hills or adjustments to speed without downshifting. So I created an acceleration chart for each of 2nd through 6th gears, showing the entire rpm range of each gear.

After the charts, I'll provide some examples of interesting comparisons you can do by cross-referencing between these charts.

**** BEFORE YOU LOOK AT THE CHARTS AND DRAW CONCLUSIONS ****

Some things to keep in mind:

These dyno charts all started around 2000 rpm, so I obviously can't show you how the Jeep would accelerate in 5th gear at 1500 rpm, for example. This is why you'll see the charts starting at fairly high road speeds in the higher gears.
The scale for acceleration is "zoomed in" progressively further for each higher gear. It's very important to keep scale in mind. For example, you'll see that at 70mph in 6th gear, the Magnuson can accelerate about twice as fast as stock. TWICE AS FAST! That sounds AMAZING! But that's twice as much of a very small amount. Go out in your stock jeep at 70 mph in 6th gear (if you have a manual trans) and and push the pedal to the floor. Not very impressive at all. Twice as quick as that is still not going to be impressive at all, and you're still probably going to want to downshift.
Also on the topic of the "zoomed" acceleration scale in higher gears... margins of error are also "zoomed in", or multiplied, when viewing the data for higher gears. What looks like a significantly big difference may very well be a much smaller small difference, or vice verse, if the torque data for one power mod had some positive error, and another had some negative error. My data points from the dyno charts will also be "spread apart" across road speed more in the higher gears' charts, which is another loss of precision/accuracy.
The "legal speed" area in the charts for higher gears is in the low rpm range (2000-2500 rpm in 6th gear). These lower rpms are just after the beginning of the dyno pull, which can sometimes have some misleading results, depending on how exactly the dyno operator pressed the throttle at the beginning of the pull, and how the computer reacts/compensates for different speeds of throttle transition. This is where the least trustworthy torque data will exist.
I'm particularly suspicious of the big "hump" in the RIPP torque curve from 2000-2700 rpm. This is not at all typical of the gains usually produced by centrifugal superchargers. I would not expect such large gains from the RIPP in that RPM range. I'd really like to see if this "hump" exists in other dyno results for the RIPP.
The Prodigy torque curve is quite possibly pessimistic in the low RPM range (below 3000 rpm). My torque data for Prodigy up to about 4200 rpm is based on an old dyno chart from last summer. Since then, there have been very noticeable improvements below 3000 rpms due to updates to the tune. I'm hoping someone will soon get updated dyno results starting from low rpms with a recent version of the tune.
In summary, the low rpm acceleration in higher gears is going to be the least reliable of all the data I have presented. It's not completely useless, but be sure to treat it as "vague approximation". The precisely drawn lines on the charts will trick your brain it to really wanting to think it means the data itself is precise. RESIST THE TEMPTATION!



click for full size (http://www.uselesspickles.com/files/jeep/acceleration_2nd_stock_mag_ripp_prod_hemi.png)
http://www.uselesspickles.com/files/jeep/acceleration_2nd_stock_mag_ripp_prod_hemi.png

click for full size (http://www.uselesspickles.com/files/jeep/acceleration_3rd_stock_mag_ripp_prod_hemi.png)
http://www.uselesspickles.com/files/jeep/acceleration_3rd_stock_mag_ripp_prod_hemi.png

click for full size (http://www.uselesspickles.com/files/jeep/acceleration_4th_stock_mag_ripp_prod_hemi.png)
http://www.uselesspickles.com/files/jeep/acceleration_4th_stock_mag_ripp_prod_hemi.png

click for full size (http://www.uselesspickles.com/files/jeep/acceleration_5th_stock_mag_ripp_prod_hemi.png)
http://www.uselesspickles.com/files/jeep/acceleration_5th_stock_mag_ripp_prod_hemi.png

click for full size (http://www.uselesspickles.com/files/jeep/acceleration_6th_stock_mag_ripp_prod_hemi.png)
http://www.uselesspickles.com/files/jeep/acceleration_6th_stock_mag_ripp_prod_hemi.png


Now for some interesting example comparisons between charts...

Want to experience for yourself approximately how one of these power mods might feel? If you have a manual transmission, YOU CAN! Well... only if you have approximately the same tire-size-to-axle-gear-ratio ratio as me. My ratio is about 28.5 (tire diameter) / 3.21 (axle ratio) = 8.88. Multiply that number by your axle ratio to find out what tire size would be exactly equivalent. For example: 8.88 * 3.73 = 33.1, so a tire diameter close to 33" with 3.73 gears will have about the same relationship between engine speed and road speed as used in these charts. Follow these steps.
1) Pick a combination of speed, gear, and power mod. For example, 70 mph, 6th gear, Hemi.
2) Take note of the G-force for that combination on the appropriate chart: Just under 0.1 G for my example.
3) Look the stock acceleration on the other charts at 70 mph, looking for one that is around the same amount of acceleration: 4th gear is the closest match for my example.
4) Now go out on the road at 70 mph in 4th gear. The amount of available acceleration at that point is similar to how it would feel in 6th gear with the 6.4 Hemi!

NOTE 1: For some combinations, you won't find a close match at the same exact speed in another gear on the stock acceleration curve. In this case, you can just find where the stock acceleration IS a close match at some other speed, then go test at that speed in that gear. For example, The Hemi accelerates at about 0.175 G at 95 mph in 4th gear. The stock wrangler accelerates the same amount at about 45 mph in 3rd gear. So the amount of "pull" you feel at 45 mph in 3rd gear in a stock wrangler is similar to how much pull you would feel with a 6.4 Hemi at 95 mph in 4th gear!

NOTE 2: These acceleration graphs will generally scale down with additional weight. Because of aerodynamic drag, it's not quite a direct relationship, but you can still look at the relative/percentage differences for a close approximation for a heavier jeep.



Another interesting example is to look at a particular speed across multiple gears, and see how each mod stacks up against the others at the same speed, and how that changes in different gears. The two most polarized options are Prodigy vs Magnuson, so they will have the most extreme variations through the different gears.

For example, 70 mph:

In 6th gear, 70 mph, Hemi is king, and Prodigy... well, not so much at all. RIPP and Magnuson are doing much better than Prodigy here too.
In 5th gear, 70 mph, Prodigy and RIPP are now essentially the same, Magnuson is better, and Hemi is still king.
In 4th gear, 70 mph, Prodigy and Magnuson are now on par with each other, both doing better than RIPP, but still taking a beating from the Hemi.
In 3rd gear, 70 mph, Prodigy has taken the throne from the Hemi, and both RIPP and Magnuson on par with each other way below the Hemi.



Again, keep in mind all the things I warned you about at the beginning of this post. And really think hard about what you really want out of a power mod before making a decision.

It's actually quite amazing to have such a wide range of options available for the Wrangler. There really is something for everyone. Between Magnuson, RIPP and Prodigy, there's quite a range of options for balance between having low-end torque for less downshifting during normal driving ("feeling" very powerful at lower rpms) at the expense of maximum acceleration potential (Magnuson), all the way to huge maximum acceleration potential at the expense of low rpm torque such that more downshifting is required to access the fun (Prodigy), with a good compromise in the middle (RIPP). Then there's the 6.4 Hemi, which nearly allows you to have your cake and eat it too (low rpm torque AND huge max acceleration potential!), but it will cost you dearly.

[KaiserBill]

Not to rain on your parade but Centrifugal Superchargers were the preferred type of forced induction systems on large aircraft engines for about 4 decades-- and these engines operated their entire lives between 1000-3000rpm. The key to the performance of a centrifugal unit is the gear-ratio or ratios the unit uses to spin the compressor (some units where two or three speeds). Since Ripp might have asked for a specific gear ratio in the gearbox from Vortec it is hard to say that you find performance at x rpm hard to believe without knowing more about Ripp's specific setup.

[UselessPickles]

You may think you are raining on my parade. But in reality, my parade has already gone by and the lingering crowds of people are watching as you stand in the middle of the street pissing fiercely into the wind.


I'm not saying that a centrifugal supercharger in general is not capable of producing big gains at low rpm, ever, on any engine, with any configuration. As you said, it's just a matter of the supercharger's gearbox ratio.

However, we are speaking specifically about a centrifugal supercharger that is known to produce a peak boost of about 7-8 psi on an engine that revs up to 6500 rpm.

The boost produced by a centrifugal supercharger is directly proportional to the square of the speed of the supercharger, and therefore directly proportional to the square of the speed of the engine.

Due to the fact that increasing engine speed reduces the amount of time available for air to flow in the intake valves, the gain in torque of a centrifugal supercharger ends up being approximately directly proportional to the speed of the engine (not the square of the speed of the engine, as the boost pressure is). This means an approximately linearly increasing gain in torque across the entire rpm range.

Again, that is approximately linearly increasing torque gains, starting with minimal gains at very low rpm, increasing fairly steadily to maximum gains at/near maximum engine speed (gains may taper off a bit near max engine speed due to the compressor falling out of its efficiency range).

Armed with this knowledge of how centrifugal superchargers work, and within the context of the entire RIPP torque curve across the rpm range, I can quite confidently say that the large bump/hump in the torque curve at low rpms is unexpected. See the following picture where I have circled the area in question, and drawn a line that approximates a reasonable expectation for the shape of the torque curve. I'm not saying the shape of the torque curve is impossible. It could be something about tuning, relative to the stock tune being intentionally de-tuned in that area for various emissions/efficiency reasons, etc.. I'm just saying just that it's unexpected, so I'd like to see whether other people have gotten similar results to see if this "hump" is consistent, or is this just a misleading side-effect of how this specific dyno run was performed.

http://www.uselesspickles.com/files/jeep/torque_ripp_bump.png


The truth is most likely somewhere in between.I'm also a bit suspicious of the dip in the stock torque curve in that same area (I've seen other stock dyno charts without this dip). If we assume that dip in the stock torque curve is a fluke, then this is about what I would expect from the RIPP torque curve:


http://www.uselesspickles.com/files/jeep/torque_ripp_bump2.png

[KaiserBill]

You may think you are raining on my parade. But in reality, my parade has already gone by and the lingering crowds of people are watching as you stand in the middle of the street pissing fiercely into the wind.


I'm not saying that a centrifugal supercharger in general is not capable of producing big gains at low rpm, ever, on any engine, with any configuration. As you said, it's just a matter of the supercharger's gearbox ratio.

However, we are speaking specifically about a centrifugal supercharger that is known to produce a peak boost of about 7-8 psi on an engine that revs up to 6500 rpm.

The boost produced by a centrifugal supercharger is directly proportional to the square of the speed of the supercharger, and therefore directly proportional to the square of the speed of the engine.

Due to the fact that increasing engine speed reduces the amount of time available for air to flow in the intake valves, the gain in torque of a centrifugal supercharger ends up being approximately directly proportional to the speed of the engine (not the square of the speed of the engine, as the boost pressure is). This means an approximately linearly increasing gain in torque across the entire rpm range.

Again, that is approximately linearly increasing torque gains, starting with minimal gains at very low rpm, increasing fairly steadily to maximum gains at/near maximum engine speed (gains may taper off a bit near max engine speed due to the compressor falling out of its efficiency range).

Armed with this knowledge of how centrifugal superchargers work, and within the context of the entire RIPP torque curve across the rpm range, I can quite confidently say that the large bump/hump in the torque curve at low rpms is unexpected. See the following picture where I have circled the area in question, and drawn a line that approximates a reasonable expectation for the shape of the torque curve. I'm not saying the shape of the torque curve is impossible. It could be something about tuning, relative to the stock tune being intentionally de-tuned in that area for various emissions/efficiency reasons, etc.. I'm just saying just that it's unexpected, so I'd like to see whether other people have gotten similar results to see if this "hump" is consistent, or is this just a misleading side-effect of how this specific dyno run was performed.

http://www.uselesspickles.com/files/jeep/torque_ripp_bump.png


The truth is most likely somewhere in between.I'm also a bit suspicious of the dip in the stock torque curve in that same area (I've seen other stock dyno charts without this dip). If we assume that dip in the stock torque curve is a fluke, then this is about what I would expect from the RIPP torque curve:


http://www.uselesspickles.com/files/jeep/torque_ripp_bump2.png


Not even wrong!


1) Centrifugal Superchargers have a gearbox so they can produce optimal compressor speeds no matter the speed of the crankshaft. So, let's say you have a 4.5:1 ratio gear box on the back end of this hypothetical CS unit-- that will give you 4.5 x times the input rpm. So let's say at 2000x4.5 gives you compressor speed of 9000rpm. This might create depending on the units size anything from 0.5-2.0psi in manifold pressure, but here is the big issue that you never seem to get this unit might be capable of putting out at >2.1psi 10-15lbs-minute of air mass-- which is what makes it possible to burn more fuel and more air at those low pressures.

2) Volumetric Efficiency is usually lower as well at low rpms in an engine and higher at higher rpms. So, let's say you have in our hypothetical engine at 14.7psi (standard one atmosphere at sea level) an air mass of 50lbs-minute being processes by each cylinder. If this is say 50% the engines maximum volumetric efficiency for Normal Aspirated induction. So, since the cylinder has 50% less air mass in it it is very easy to squeeze in 10-25 lbs-minute of air mass into the cylinder without really needing 20PSI to do so. So you can boost volumetric efficiency very easily at this point. So going to 65lbs-minute air mass is an increase of 15% in Volumetric Efficiency.

3) As the engine increases its efficiency as it increases RPM-- the amount of boost needed to reach higher and higher Volumetric efficiency ratings requires higher boost! So, to squeeze more air into the cylinder you have to use more PRESSURE or combine that with an increase in the size of the combustion chamber- i.e. reduce compression ratio usually via piston design.

4) Torque gains might not be minimal at low the end of the RPM spectrum... Again you can alter the horsepower and torque gains by changing the size of the unit and gearbox ratios to fit the needs.

5) The hump isn't what is odd-- it is the dip after it that is far more telling... The hump is pretty expected. The Dip, says that something in the engine radically changes and the super is no longer as efficient in supplying the required air-mass to maintain sufficient combustion to create the same levels of power. It could be that Vortec unit isn't able to keep pace with the rising Volumetric performance of the engine between 2400-2900rpm. It is boosting the performance over stock but the unit isn't keep up with the engine's own internal pressure. It could be related to only this unit. If you chart is right it isn't giving the supposedly expected 300ft-lbs of torque at the rear wheels either. That is odd too.

6) Like I said the units gearbox pretty much makes it impossible to use your squared proportional formula and get any meaningful data for generalization. What is really important is knowing how the gearboxes ratios affect the compressors speed for a given rpm and that has nothing to do with the square of the engine's rpm. The the impeller itself will be rotating at different velocities from the centripetal forces of the air being pressed against housing. Sure, you need to use the square of the radius impeller itself. But for just figuring out the actual impeller's increase in rpm over that of the input shaft-- that is simple multiplication. Ratio times input rpm!!!

8) Not all superchargers are created equal-- however, to determine what sort of Volumetric Efficiencies, Boost Ratings and Adiabatic Efficiency also known as Parasitic Efficiency...

9) Finally, I'm still trying to figure out what in the hell you are talking about with the valves. Is just puzzling it sounds like you're talking about the engine's VE but combining that with valve surge. Here is the thing like any device it has a small spectrum of efficiency where it reaches nearly maximum theoretical performance and then it falls off.

10) It's been a blast...

11) You do need more samples in your data set to make any general statement at all about these modifications and performance... That is a fact. Also you need better testing methods i.e. you first have to determine is your stock engine making advertized torque and hp at the crankshaft before you turbo it and then do it with the modification. Then get data on the drive train and then work it with the turbo unit replace it into the Jeep and do the same tests. Otherwise all you're doing is guessing. But I can tell you this for your 33% loss figures to be accurate would mean that you have to have 585HP at the Crankshaft for a 360ish WHP ratings... You're not getting 585Hp at the crankshaft without doing some serious modifications to the engine internally. NRE is getting those sort of numbers on pump gas, but, they are totally blue printing the engine to do that sort of thing! That is not the power you're getting from a bolt on modification and 93 pump gas. IT is more likily you're getting 90-120hp at most and only loosing 60-80hp.

[UselessPickles]

Not derp derpy!


1) Duuurp Derpity duuurp a duuurp so duuurp can derp derpy derpy hodor no duuurp the derpity of the derpy. So, let's say you derpy a 4.5:1 derp derpity box on the derpy end of derpity derpity CS derpy-- duuurp derpity derp you 4.5 x derpy the derpity rpm. So let's say at 2000x4.5 derpy you duuurp derpity of 9000rpm. Derpity derpy derpy derpity on the derpy hodor duuurp derp 0.5-2.0psi in derpity derpity, but derpity is the big derp derpy you derp duuurp to get duuurp duuurp derp be derpy of derpity out at >2.1psi 10-15lbs-derpy of air duuurp-- derp is derpity derpity it hodor to duuurp derpity derpity and duuurp air at derpy low derp.

2) Derp Derpity is derpity derpy as duuurp at low derpy in an duuurp and duuurp at derpy derpy. So, let's say you duuurp in our derpy derpity at 14.7psi (derpity one derpy at sea duuurp) an air derpy of 50lbs-derp derpity hodor by derpity derpity. If duuurp is say 50% the derpity duuurp duuurp derpity for Duuurp Duuurp derp. So, derpity the derpy has 50% derp air derp in it it is derpy derpity to derp in 10-25 lbs-derpity of air derpity derp the derp derpy duuurp duuurp 20PSI to do so. So you can derpy duuurp derp duuurp derpity at duuurp duuurp. So duuurp to 65lbs-duuurp air hodor is an derpity of 15% in Derpity Derpity.

3) As the derp derpy its duuurp as it derpy RPM-- the derpity of duuurp duuurp to duuurp hodor and derpy Derpity derp duuurp derpity duuurp derpy! So, to derpy derp air duuurp the derpy you derpy to use derpity DERPY or derpity derpity derp an derp in the derp of the derpity duuurp- i.e. duuurp derpy duuurp derpy via derp derpy.

4) Derpity derpity duuurp not be derpity at low the end of the RPM derp... Derpity you can duuurp the derp and derpy derpy by derpy the derp of the derp and duuurp derpy to fit the duuurp.

5) The derpy isn't derp is odd-- it is the dip derp it derp is far duuurp derpy... The derpy is derpy duuurp. The Dip, derpity duuurp duuurp in the derpity derpity derp and the duuurp is no derpy as derp in derpy the derp air-derpity to derpy derp derpity to derpity the derp derp of derp. It derp be derpity Derpity derpy isn't duuurp to duuurp derpy derpy the duuurp Duuurp derpy of the derpity derp 2400-2900rpm. It is hodor the derp duuurp derpy but the derpy isn't duuurp up duuurp the derpity's own duuurp derp. It duuurp be derpity to derpy duuurp derpy. If you derpy is duuurp it isn't duuurp the derpity derp 300ft-lbs of duuurp at the derpy derp duuurp. Derpy is odd too.

6) Derpity I derpity the derpy derpity derpy derpity duuurp it derpy to use derpy duuurp duuurp derpity and get any derpity duuurp for duuurp. Derpy is duuurp derpity is derpity how the derp derpity duuurp the duuurp derp for a derp rpm and derpity has derp to do derpity the derpity of the derpity's rpm. The the derpity duuurp derpity be derpy at derp derpity derpity the derp derpity of the air duuurp derpity derp hodor. Duuurp, you derp to use the derp of the duuurp hodor derpity. But for duuurp derp out the derpity duuurp's derpity in rpm derpy derpy of the derp derpy-- derpy is duuurp hodor. Derpy derpity derpy rpm!!!

8) Not all derpity are derp derpy-- derpy, to derp derp derp of Derp Derpy, Duuurp Derp and Derp Derpity derpity derpity as Derpy Derpy...

9) Derpy, I'm derpity derpy to duuurp out derpity in the derpy you are derp derp derp the derpity. Is derpity duuurp it duuurp derp you're derp duuurp the derpy's VE but derpy derpy hodor derpy derp. Duuurp is the derp duuurp any derpity it has a derp derpy of derp derpity it derpy derpity duuurp derp derp and derpy it derpy off.

10) It's derp a hodor...

11) You do derpy hodor derp in derpy duuurp set to duuurp any derpity derp at all hodor derpity duuurp and derpity... Derpy is a derpy. Derp you derpity duuurp hodor duuurp i.e. you derpity derpity to duuurp is duuurp derpy derp derp derp derpy and hp at the derpity duuurp you derpity it and derpy do it derpity the derpity. Derp get derpy on the derpity derp and duuurp derpity it duuurp the derpity derp derpy it derpity the Duuurp and do the derpity duuurp. Derpy all you're derpity is derpy. But I can derpy you derpity for derp 33% duuurp derpity to be derpity derpity derpy duuurp you duuurp to derp 585HP at the Derpity for a 360ish WHP duuurp... You're not derpy 585Hp at the derp duuurp derpy derp duuurp derp to the derp derp. NRE is derpity derpity derpy of duuurp on hodor gas, but, derpity are duuurp derp derpity the derpity to do derpity duuurp of derp! Derp is not the derpy you're derpity derpity a derpity on duuurp and 93 derp gas. IT is duuurp derp you're derp 90-120hp at derpy and derpy duuurp 60-80hp.

Just a reminder that this is what all of your posts now look like to me. This helps prevent me from wasting my time trying to actually discuss/debate your mostly irrelevant, non-interrelated, and/or just plain incorrect points.

If anyone thinks any of KaiserBill's points are valid or worth discussion, please re-post any specific questions you have that you would like me to respond to :)

[KaiserBill]

Just a reminder that this is what all of your posts now look like to me. This helps prevent me from wasting my time trying to actually discuss/debate your mostly irrelevant, non-interrelated, and/or just plain incorrect points.

If anyone thinks any of KaiserBill's points are valid or worth discussion, please re-post any specific questions you have that you would like me to respond to :)

You might try reading books on engine design and turbo-super charging design instead of eating them.

[Timmy]

You hodor try duuurp derpity on derp derpy and derpy-derp duuurp derpity derp of derp derp.

You hit the head on the nail KaiserBill. A brilliant little piece of coding if I do say so myself.

[KaiserBill]

I t s u i t s y o u r l e v e l o f t e c h n i c a l a b i l i t i e s w e l l ...

[Pznivy]

You may think you are raining on my parade. But in reality, my parade has already gone by and the lingering crowds of people are watching as you stand in the middle of the street pissing fiercely into the wind.


I'm not saying that a centrifugal supercharger in general is not capable of producing big gains at low rpm, ever, on any engine, with any configuration. As you said, it's just a matter of the supercharger's gearbox ratio.

However, we are speaking specifically about a centrifugal supercharger that is known to produce a peak boost of about 7-8 psi on an engine that revs up to 6500 rpm.

The boost produced by a centrifugal supercharger is directly proportional to the square of the speed of the supercharger, and therefore directly proportional to the square of the speed of the engine.

Due to the fact that increasing engine speed reduces the amount of time available for air to flow in the intake valves, the gain in torque of a centrifugal supercharger ends up being approximately directly proportional to the speed of the engine (not the square of the speed of the engine, as the boost pressure is). This means an approximately linearly increasing gain in torque across the entire rpm range.

Again, that is approximately linearly increasing torque gains, starting with minimal gains at very low rpm, increasing fairly steadily to maximum gains at/near maximum engine speed (gains may taper off a bit near max engine speed due to the compressor falling out of its efficiency range).

Armed with this knowledge of how centrifugal superchargers work, and within the context of the entire RIPP torque curve across the rpm range, I can quite confidently say that the large bump/hump in the torque curve at low rpms is unexpected. See the following picture where I have circled the area in question, and drawn a line that approximates a reasonable expectation for the shape of the torque curve. I'm not saying the shape of the torque curve is impossible. It could be something about tuning, relative to the stock tune being intentionally de-tuned in that area for various emissions/efficiency reasons, etc.. I'm just saying just that it's unexpected, so I'd like to see whether other people have gotten similar results to see if this "hump" is consistent, or is this just a misleading side-effect of how this specific dyno run was performed.

http://www.uselesspickles.com/files/jeep/torque_ripp_bump.png


The truth is most likely somewhere in between.I'm also a bit suspicious of the dip in the stock torque curve in that same area (I've seen other stock dyno charts without this dip). If we assume that dip in the stock torque curve is a fluke, then this is about what I would expect from the RIPP torque curve:


http://www.uselesspickles.com/files/jeep/torque_ripp_bump2.png

So you are saying the RIPP curve is wrong? it should be linear, i get that. but JL has done a bunch of dynos, is it consistent? or is it there sometimes and not others?

Could any air at all above sea level push the pentastar past its factory power levels?

[UselessPickles]

I am not and cannot say that the RIPP power curve is wrong. Only that it is unexpected based on how centrifugal superchargers work, and in comparison to dyno charts of other centrifugal supercharged vehicles I have seen.

Sounds like we need some input from Ross: do all of your dyno pulls for Black Betty have this "hump" in the torque curve at low rpms?

Also, I vaguely remember something about fixing a small leak and getting more power. Do you have dyno results with more power? If so, please email the dyno run file so I can import the the torque curve data and update my charts, etc.

[UselessPickles]

Could any air at all above sea level push the pentastar past its factory power levels?

I'm guessing you meant to say "any amount of boost at all above atmospheric pressure"?

More pressure = more air. So, yes, in general, any amount of boost above atmospheric pressure should theoretically be able to produce some amount of increase in engine output.

[JeepLab]

BB has been dyno'd a bunch of times. I'll dig up a file, we should probably start a dyno thread. And post all the charts in one spot.