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-sh...sults-89983/#b

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

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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:

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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.

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[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; 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.

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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:

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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:

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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)

[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?



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