to talk to this point of 3rd vs. 4th gear, I cannot tell the difference when looking at the charts weather a dyno pull is 3rd gear or 4th gear unless you change the charts parameters to actual speed MPH, and not engine speed RPM.

Otherwise, you could end up laying 3rd gear runs over 4th gear runs and not know that its not apples to apples, in the RPM band, it looks like apple to apples.

Ross - I think you are talking about your 3rd and 4th gear stock dyno runs. I'm talking about Jessee's 3rd and 4th gear turbo dyno runs. The gear made a pretty big difference with the turbo. Want me to post a chart comparing them?

Originally Posted by UselessPickles

Ross - I think you are talking about your 3rd and 4th gear stock dyno runs. I'm talking about Jessee's 3rd and 4th gear turbo dyno runs. The gear made a pretty big difference with the turbo. Want me to post a chart comparing them?

3rd gear definitely showed lower peak number than 4th. This was 100% expected by the shop rolling the dyno and by me. Again - its the idea that a dyno is most accurate where a 1:1 ratio is achieved. I didn't do the math to figure out what gear had my 1:1, I just assumed I should use 4th as was done previously.

My higher axle gearing would have skewed my numbers down vice the factory 4.10s in a given gear. The higher gearing changes the engine's rate of acceleration as a matter of fact. Faster engine acceleration equals lower bhp. Again - the effect of this is different for every dyno manufacturer and the way it does its math.

I'm feeling another dyno run is in my future.

Ok, here it is. Jessee's torque curve in both 3rd (blue) and 4th (red) gear:

Attachment 976

If the pattern continues, I bet a 5th gear pull (which due to 4.88 gears, would be similar to a 4th gear pull on stock gears/tires) would result in an even earlier and higher torque peak that has a shape more like Prodigy's results.

If i can get Prodigy to email me the install manual for the stage 2 upgrade, i can get my dyo passes in.. It was supposed to be today but the shop wouldnt begin without the Manufactures instruction manual. So i had to reschedule for tomorrow, anticipating ill get my hands on the install manual. I have an automatic with 5.13 37" mud grapplers. They will be doing dyno before the install and after the install. Again this is whether or not ill get the install instructions.

Originally Posted by UselessPickles

Ok, here it is. Jessee's torque curve in both 3rd (blue) and 4th (red) gear:

Attachment 976

If the pattern continues, I bet a 5th gear pull (which due to 4.88 gears, would be similar to a 4th gear pull on stock gears/tires) would result in an even earlier and higher torque peak that has a shape more like Prodigy's results.

I had a conversation with wes today at length. A 5th gear dyno run would bring the truck to like 150 mph. Its out of the question.

4th gear is the closest to 1 to 1 and the axle gear ratio is a non factor.

Its not going to make 40 more hp if you run it in 5th.

Originally Posted by NOLAjeeper

If i can get Prodigy to email me the install manual for the stage 2 upgrade, i can get my dyo passes in.. It was supposed to be today but the shop wouldnt begin without the Manufactures instruction manual. So i had to reschedule for tomorrow, anticipating ill get my hands on the install manual. I have an automatic with 5.13 37" mud grapplers. They will be doing dyno before the install and after the install. Again this is whether or not ill get the install instructions.

I just sent a message. Trying to nip this missing manual thing.

Originally Posted by JeepLab

A 5th gear dyno run would bring the truck to like 150 mph. Its out of the question.

Not gonna happen!

Originally Posted by NOLAjeeper

If i can get Prodigy to email me the install manual for the stage 2 upgrade, i can get my dyo passes in.. It was supposed to be today but the shop wouldnt begin without the Manufactures instruction manual. So i had to reschedule for tomorrow, anticipating ill get my hands on the install manual. I have an automatic with 5.13 37" mud grapplers. They will be doing dyno before the install and after the install. Again this is whether or not ill get the install instructions.

This will be good info. I"m really looking forward to it.

Originally Posted by JeepLab

I had a conversation with wes today at length. A 5th gear dyno run would bring the truck to like 150 mph. Its out of the question.

4th gear is the closest to 1 to 1 and the axle gear ratio is a non factor.

Corrections:
5th gear is exactly a 1:1 ratio on the manual transmission.
5th gear with stock tires and 4.88 gears (the way Jessee put his jeep on the dyno) would max out at 122 mph at 6500 rpm.
5th gear with his 37 inch tires and 4.88 gears would max out at 141 mph.

For comparison:
4th gear with stock tires and 3.73 gears would max out at 128 mph.
4th gear with stock tires and 3.21 gears would max out at 148 mph.

Therefore:
Jessee's jeep with stock tires in 5th gear is similar to a stock jeep with 3.73 gears in 4th gear.
Jessee's jeep with his 37" tires in 5th gear is similar to a stock jeep with 3.21 gears in 4th gear.


Information calculated using: http://www.grimmjeeper.com/gears.html
Using 30.75" as the actual mounted diameter of stock tires and 35.5" as the actual mounted diameter of the 37" tires.

Originally Posted by JeepLab

the axle gear ratio is a non factor

As Jessee's dyno results show, overall gear ratio does matter on that dyno, the way the dyno run was performed. The results are very different between 3rd and 4th gear. There is no way you can look at those results and conclude that the gear ratio is a non factor.

A difference in axle ratio causes a difference in overall gear ratio essentially just the same way a different transmission gear causes a difference in overal gear ratio. If axle ratio was a non factor, then transmission ratio would also be a non factor. If the overall gear ratio matters, then the entire combination of transmission gear, axle ratio, and tire size all matter.

Originally Posted by UselessPickles

As Jessee's dyno results show, overall gear ratio does matter on that dyno, the way the dyno run was performed. The results are very different between 3rd and 4th gear. There is no way you can look at those results and conclude that the gear ratio is a non factor.

A difference in axle ratio causes a difference in overall gear ratio essentially just the same way a different transmission gear causes a difference in overal gear ratio. If axle ratio was a non factor, then transmission ratio would also be a non factor. If the overall gear ratio matters, then the entire combination of transmission gear, axle ratio, and tire size all matter.

I said Axle Gear is a non factor. Not transmission gear. The dyno connects to the cpu in the dash and uses the RPM of the engine to correct for the speed of the tumbler

Stock jeeps get dyno'd in 3rd gear because the stock tune hits the speed limiter in 4th.

Modded Jeeps get dyno'd in 4th, as it is closest to 1 to 1 ratio. I have never heard anywere of a jeep getting dyno'd in 5th gear.

Ive been at this a while, and have interviewed and worked with every power mod manufacturer. They all say the same thing.

Dynojet both drum speed and engine speed are measured and used to take out any effects of gear torque multiplication.

Ive been searching for about 40 min now, and cannot find a clear final answer about the inner working of the dynojet. Ive read arguments from both sides of this in other forums and there is no clear post that would settle this.

I will call dynojet tomorow and make them email me a response I can post.

I didn't misquote you (that wan't a quote where I said "overall gear ratio"). I was trying to bring attention to the fact that it is the overall gear ratio that caused the difference in Jessees results. Transmission ratio and axle ratio both contribute to overall gear ratio.

It doesn't matter whether the difference in gear ratio is in the transmission or in the axle. A difference in gear ratio is a difference in gear ratio. If one matters, then the other matters. There's no way around it. The overall gear ratio is the transmission gear ratio multiplied by the axle gear ratio. One is not not inherently more significant than the other just because of its physical location. If you agree that transmission ratio is a factor, then you are also agreeing that axle ratio is a factor.

4th gear is a 1.25:1 ratio.
5th gear is a 1:1 ratio.

How is 4th gear "closest to 1 to 1 ratio" if 5th gear is EXACTLY 1 to 1?

The difference between 4th and 5th gear is 25%. The difference between 3.21 axle and 4.88 axle is 52%. The difference between 3.73 axle and 4.88 axle is 30%. The difference between Jessee's axle ratio and stock axle ratios is MORE significant than the difference between 4th and 5th gear!

AGAIN: This is is a special situation to turbos only, because it's related to the amount of load on the engine and the duration of the dyno pull allowing the turbo to spool up. This is not about the typical factor of drivetrain rotational inertia. I agree that the axle ratio (and transmission gear) would have minimal effect on a naturally aspirated or supercharged engine, because they do not depend on engine load to produce power.

The turbo needs engine load and time to spool up. The amount of load on the engine on a simple inertia dyno is primarily directly proportional to the overall gear ratio from the engine to the dyno drum (including transmission gear ratio, axle gear ratio, AND tire size). It's the overall ratio between engine speed and "road speed" that matters here.

This also all only matters on an acceleration sweep dyno pull (which is the only type that an inertia dyno can perform). If we could get steady state results on a load bearing dyno, then we wouldn't have to worry about any of this (tire size/weight, gear ratios, etc).

We already have a test that shows that gear ratio matters hugely on the dyno that Jessee used. His dyno results clearly fit the my explanation of the turbo spooling up more slowly with respect to engine speed when using gearing that creates less load on the engine.

All the people that have all told you that axle ratio doesn't matter... was it clearly being discussed in the context of a turbocharged vehicle on an inertia dyno (or sweep test on a load dyno)? it's not a matter of either me being right or them being right. Context is key. Their statements are true in many contexts. Their statements are false in this specific context of a turbocharged vehicle on an inertia dyno (or in a sweep test on a load dyno).

Originally Posted by JeepLab

Ive been searching for about 40 min now, and cannot find a clear final answer about the inner working of the dynojet. Ive read arguments from both sides of this in other forums and there is no clear post that would settle this.

I will call dynojet tomorow and make them email me a response I can post.

It will depend on exactly which model of dynojet dyno. Some are inertia dynos, others are load bearing dynos.

Simple inertia dynos are only capable of acceleration sweep tests, and the load is simpy the mass of the dyno drum. This type of dyno is 100% guaranteed to have the problems I'm trying to describe with significantly different results with a turbocharged vehicle with different transmission and/or axle ratios. Rotational inertia of the drivetrain/tires/etc also affects the readings on these dynos, 100% guaranteed.

Load bearing dynos are capable of performing steady state dyno pulls, where it holds the engine steady at full throttle and records the amount of load (torque) was required to hold the engine at a steady rpm (rinse and repeat for many different engine speeds, and you get data points to form a cull rpm range dyno chart). This would give consistent results no matter what transmission gear, axle ratio, or tire size was used, because there is no torque lost to accelerating those components (so therefore no differences in the amount of torque lost to accelerating different configurations of those components), and the turbo lag would not be an issue either because the turbo would be allow to spool up at each rpm point and reach equilibrium before the measurement is taken.

Load bearing dynos can also perform acceleration sweep tests, but can be configured to perform the sweep in different ways. This is even more complicated than a sweep test on an inertia dyno, because at least an inertia dyno can only operate in one mode. The results of a sweep test on a load dyno can be affected by a combination of gear ratios, tire size/weight, AND how the dyno operator configured the dyno to operate (slower sweep with more load? faster sweep with less load? constant load? varying load to achieve constant rate of acceleration?).

Yes, it's a big mess

So there's a catch 22 here.

A steady state dyno chart is the only way to get guaranteed consistent and comparable dyno results (regardless of gears, tires, etc).

But a steady state dyno chart is arguably not "realistic", because we use the torque/power of our engines primarily to ACCELERATE... not to maintain steady state speed. A tiny fraction of the peak power is actually required to maintain steady speed. A steady state dyno chart will show the highest results of all, but you will never experience that amount of torque/power while accelerating on the street.

When accelerating on the street, some of that torque/power gets used up to accelerate the drivetrain and wheels. The faster you accelerate (i.e., lower transmission gear), the more of the torque/power is lost to accelerating the drivetrain and wheels.

With a turbo, the effect is compounded by the turbo spooling more slowly when under less load in lower transmission gears. Or you can look at it from the other direction and be happy that with higher transmission gears, the turbo has the advantage of spooling up more under higher load to produce some more power, making up for some of the loss of torque multiplication from upshifting to a higher gear

(I've actually noticed that compared to my expectations based on how 1st and 2nd gear feel, 3rd pulls VERY strong all the way up to redline, without ever feeling like it's losing steam due to increasing air resistance.)


So what people really care about is a representation of how the vehicle will accelerate on the street. It makes sense that the best dyno test would be one that mimics acceleration on the street.

Load bearing dynos can be configured to perform sweep tests that simulate actual acceleration on the street, by dynamically adjusting the load of the dyno throughout the test to simulate both the load of the weight of the vehicle, and the load of air resistance (which increases with speed, proportional to the square of speed). This only works well if the dyno is accurately configured with the vehicle's weight and aerodynamic drag constant (drag area). I know Mustang dynos work this way. I'm not sure if the load bearing Dynojet dynos can do this. Even if you configure the dyno accurately, you still have problems. Which gear do you use? Do you simulate a fast 1st gear acceleration, which will give the lowest results (due to larger rotational inertia losses from the drivetrain, and slower spooling turbo with respect to engine speed), but most accurately represent the most acceleration you'll ever feel from the vehicle? Do you simulate acceleration the highest gear that can reach the rev limiter, which would give the highest results (least rotational inertia loss, turbo spooled more fully at lower rpms), but not accurately represent the power you will use in everyday driving? Or do you go with some middle gear for a balance of impressive numbers and realistic representation of what you'll experience most often on the road? Different jeeps with different tires and axle ratios would also produce different results on this type of dyno pull, which would accurately reflect their affect on real world driving performance.

The Dynojet response is at the top, my question is at the bottom.

Ross,

The reading (as you call it) will most likely be different because the work performed by the Jeep will different with different rear gears.
Even without changing the rear gear, you can make a run in 3rd and another in 4th and so on and they will show different HP.
But think about what is going on here---
the computer is monitoring the acceleration of the dyno drum, it has no idea what type of vehicle is on it or what gear it is in.
Measuring Rear Wheel HP where the tire touches the drum means any change made before the drum has the potential to change the RWHP .

Above is some theory to ponder.
Please don’t believe everything you read in forums.

Thanks,
Bill


From: ross@jeeplab.com [mailto:ross@jeeplab.com]
Sent: Monday, August 11, 2014 7:59 PM
To: dynotech@dynojet.com
Subject: Dynamometer Tech. Inquiry

Entered on: http://www.dynojet.com/Contact/Dynojet-sales.aspx

Submitted On: 8/11/2014 10:58:33 PM
-----------------------------------------------------------------------------------
Regarding: Model 224x
-----------------------------------------------------------------------------------
Name: ross
Email: ross@jeeplab.com
Country: United States
Comments: Im from JeepLab.com and we are dyno testing a new turbo Jeep Wrangler with a dynojet. The argument in the forum right now is weather or not the axle gear ratio will alter the dynojet's reading. Will 3.21 gearing give a different dyno reading than 4.88 gearing assuming all other variables are the same? Thank you!

Soooooooooooooooo where do we go from here?

NOLA, Did you ever get the instructions?

We will need the stats on the NOLA jeep to compare to JG for a point of reference?

Nope did not get the instruction manual. I'm out of town until Sunday.. I dropped my rig off Tuesday morning without the instruction manual, and emailed Dan at prodigy .. Told him I had dropped off the jeep and the shop was waiting for his instructions.. Haven't heard from the shop or prodigy. So I am assuming everything is going well. I will update whenever I get additional info.

Originally Posted by NOLAjeeper

Nope did not get the instruction manual. I'm out of town until Sunday.. I dropped my rig off Tuesday morning without the instruction manual, and emailed Dan at prodigy .. Told him I had dropped off the jeep and the shop was waiting for his instructions.. Haven't heard from the shop or prodigy. So I am assuming everything is going well. I will update whenever I get additional info.

We have a wide array of pictures of the install. I'm not sure of the utility of each one. If your installers run into a challenge - post it here and I'll try to post some pictures to illustrate how it was solved in our installation. Worst case - I can get some picture of how its set up in JG and post those.