Again, people's dynos back this one up.

The lowest recorded RWHP for an MN6 C5 in the performance registry is for Hellraiser's 2001 stock coupe. He lists 306.6 RWHP, which is a loss of 12.4% (atmospheric conditions for his run were close enough to SAE standards as to not really matter.)

 

So your saying the drivetrain loss is a function of humidity, can you explain that???

 

No, dyno numbers are a function of humidity and temperature and barometric pressure.

 

Dyno backup with 1/4 mile testing.

Well we finally got a break from the weather and the track opened for test and tune. We wanted to back up our dyno results with some 1/4 runs. Stock we know the best was 13.17 @ 106MPH
On the way up to Moroso we passed through some heavy down poors and had to wait for the track to dry.
Let me first say that we picked a bad night to do it. 81 degrees, 100% humidity and 15 mph headwind.

Test car very important AUTO C6 with Vortex Ram induction system & BPP Long Tube Step Headers.

First run of the night take off from idle and left her in overdrive, TC off 12.73 @ 110.5

Second run was done from idle but manually shifting( That Didnt work!!) 1st to 2nd upshifted at 6400 but car did not shift till after it bumped the rev limiter. 2-3rd I tried to shift sooner at 6000 but the car still went past it and hit the rev, had to let go of the gas for her to shift. Found out that you cannot manually shift the C6 for racing.

Bumped the rev limit in all gears. 12.85 @ 108

Third run was done 12.70 @110
60 1.96

Forth run was done with holding the rpm up to 1500 and launching.
12.61@112
60 1.99

So far we have picked up .5 and about 6 mph going into a head wind. We hope to get the Corsa cat back to do some more testing.

We do feel on a good day we could hit 12.4 to 12.5 at over 114 mph. With a good cat back system and programming we should be in the low low 12's

In a stick car with a stock time in the 12.7 you could expect to be between 12.0 and 12.2 with those mods and maybe on a good day in the 11's.


Ernie
www.BreathlessPerformance.com

 

Sorry this is the statement I meant, I edited the wrong sentence of your quote, please explain this loss of drivetrain via humidity??

 

Again, there is no change in drivetrain loss due to humidity. Humidity alters the dyno numbers. This is because the rated BHP of the engine doesn't change. The engine is 345 SAE Net BHP.

Since we don't know what the humidity is, or whether the dyno was already SAE Corrected, the car's actual SAE Net correct HP is either one number, or within another range.

If we assume that the dyno was already corrected, then humidity doesn't matter (since it's already corrected and accounted for.) In this case, we already have the SAE Net corrected HP to compare to the engine's SAE Net BHP. 294.4 RWHP from a 345 BHP motor is a 14.7% loss through the drive train.

But if the dyno was not already SAE corrected, then we need to know the humidity. Since we don't, we can find the range within which the SAE Net corrected RWHP falls by calculating for both 0% and 100% humidity.

If the humidity was 0% at the time of the dyno, then the result was actually 3.5% higher than the SAE Net corrected number would be (due to very favorable conditions.) Corrected, we find that the engine is actually only putting 284.4* HP to the wheels under SAE's standard conditions (the same conditions that the engine's 345 HP is obtained.) This means that the car is actually losing 17.56%* through the drive train.

If the humidity was 100% at the time of the dyno, then the result was actually 1% higher than the SAE Net corrected number would be (due to slightly favorable conditions.) Corrected, we find that the engine is actually only putting 291.485* HP to the wheels under SAE's standard conditions (the same conditions that the engine's 345 HP is obtained.) This means that the car is actually losing 15.51%* through the drive train.

Notes:

1) Numbers marked with * have been slightly revised due to an earlier error in my calculations.

2) These numbers are for an A4 2000 C5 Coupe with 3.15 rear gears.

Summary: The drive train loss of this car does not change based on the humidity. Our guess as to the drive train's loss does because we don't know the humidity at the time of the dyno nor do we know if the dyno is already SAE corrected. If the dyno is SAE corrected, or if we were provided the humidity at the time of the test, we would know the drivetrain's loss.

My guess: I'm betting that the humidity was low and that the dyno numbers are not SAE corrected, as this would place the drivetrain's loss closest to the 17% that I've observed C5's with A4s and 3.15 gears having.

 

320RWHP stock?? thats very low auto or not.

 

Ok, one more question. A little fuzzy with the above statement in regard to the 345 never changing. The dyno runs I withnessed were all corrected and were all over the map on numbers, even comparing similar car stats.

 

Because, though there is natural variation from one to the next, 345 is the best number we have unless people start removing their individual engines from their cars to perform an engine brake dyno directly to it.

 

From what I've seen in the past Chevys listed horsepower numbers are very rarely correct. In fact, many times Chevy under rates some motors. Many of the Chevy high performance crate motors will dyno more power than Chevy's advertised number when put on an engine dyno. Using Chevys advertised numbers as a set in stone horsepower rating is probably not very accurate.

 

There's no way to know that. People assume that Chevy under-rates the motors because they assume that the losses are 15% for a manual and 20% for an automatic.

The only way to know for sure if the Corvette's drivetrain is more efficient, or if the engine is under-rated, is to dyno the car, immediately take the engine out, and brake-dyno the engine under the same conditions.

 

I wasn't assuming anything. I was referring to actual engine dyno tests on Chevy crate motors. Most of the big block Chevy high performance crate motors will make more power than the advertised numbers.

I don't know what the actual engine dyno numbers are on stock C5/C6 Corvette motors, but I would be surprised if they are exactly the same as the advertised numbers.

 

Should it matter what the baseline is though as long as changes & dyno's were done in the same conditions? I agree it sounds high, but I don't see what's wrong with the testing.