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Old 01-25-2011, 06:41 PM   #1
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Default Jeep Wrangler 18 dyno pulls for CAI testing

Purpose: To determine if the intake on the 4.0L jeep wrangler is a restriction that can cause a loss of hp.

Procedure: All the testing was done on the same day, while strapped down to the dyno. All conditions were tested multiple times to rule out variation in the experiment.

Datalogs: All runs were datalogged to account for ECT, IAT, MAP, Timing, etc. (logs will be evaluated soon, but they were generally all the same)

Conditions:
  • Pulls 1-5 were done on the stock intake setup
  • Pulls 6-8 were done after removing the stock "horn" on the airbox
  • Pulls 9-12 were done after increasing the tire pressure from 25psi to 55 psi. This was done to try to minimize the wavy torque curves.
  • Pulls 13-14 were done with no intake at all, just an open throttle body with the IAT sensor duct taped 2" above it.
  • Pulls 15-18 were done with the aftermarket intake.
Results:

The stock setup shows minimal variation between runs. Run 4 made the best power at 142.12 and run 3 made the best torque at 187.73.





What does this mean? Its pretty damn good, but there is still a variation that needs to be taken into account. The 3SD (99%) value is 2.79hp, so the average HP for these pulls (140.9hp) can vary between 138.1 and 143.7 hp. The Torque is similar with an average of 177.5 and a 3SD of 3.68ft-lbs. Any claims that are less than than double the 3SD value can be considered to not be statistically significant.

Runs 6-8 with no "horn" (that thing on the end of the airbox). It was suspected that such a small restriction would limit power, but nothing really changed. Average Hp is 142.1 +3.73 and Avg TQ is 176.7 + 6.06



Next we pumped up the tires to try and smooth out the TQ curves. (runs 9-12) It seemed to make it worse, but it made more power. The horn was still removed on these tests. The results were unexpected! Avg Hp went to 146.96+2.07 and Avg TQ went to 181.2+10.54. The high variation from the TQ is from the wavy data. It might be due to the "big" tires (31s), or a funky rpm signal. Are there real gains? Sort of, but they are very small.


"No intake" testing to determine the best case scenario on pulls 13 and 14 with pull 11 (the best of the tire pressure pulls) as a reference. The intake was completely removed and it was run with an open throttle body and no air filter. Avg hp was 151.72 + 2.46 and Avg TQ was 183.12 + 5.54. The stock intake costs a few hp, but not much at all.





The last 4 pulls (15-18) were with the new cowl intake. It is much louder than the stock intake and has a cool turbo type of sound as the vibrations radiate in the cowl. Runs 13 and 14 (no intake) were included as a reference. The Avg hp was 149.33 + 5.57 and the avg TQ was 185.71 + 5.74.





Summary

Code:
Condition      Avg HP      Avg TQ      3SD HP      3SD TQ
stock           140.92      177.49       2.79       3.68
No Horn         142.12      176.69       3.73       6.06
Tire pressure   146.96      181.20       2.07       10.54
No Intake       151.72      183.12       2.46       5.54
Cowl Intake     149.32      185.71       5.57       5.75
There is a couple hp worth of restriction on the intake, but its minimal. I will do some testing at freeway speeds to determine if the MAP increase at all due to the pressurized cowl. I do not expect much at all. I will say that the IATs now run much cooler and the intake is always cool to the touch. I have seen this jeeps pull up to 7* of timing for hot IAT temps during low speed off roading in the desert. There was no tuning done at all for any condition. That will be evaluated in the future.
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Old 04-02-2012, 02:40 PM   #2
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This shows how easy it is to make a dyno graph that "proves" that you made hp. Reading the above info will explain why this is BS when you factor everything in.
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Old 04-03-2014, 02:50 PM   #3
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Because this questions comes up a lot about the significance, I applied some statistics to the results. Having overlapping 3SD ranges does mean that if you ran a sufficient amount of N, you might get some overlap, but that alone does not mean that the means are not statistically significant. Using statistical software I applied the Dunnett's method using the stock condition as a control for p values less than 0.05 (95% confidence). The ones that are highlighted in red are not significant. You can see that the intake does make significantly more hp than stock.
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