Input requested from knowledgeable forum members

[Heffner Performance]

From what I can tell, you are all quite knowledgeable when it comes to the R8 so I hope t get a good number of responses to this.

I am attempting to settle a disagreement as to whether a six speed V8 R8 would show more power on a chassis dyno than an R Tronic car would, assuming all other variables are equal. Of course I have dyno numbers from both set ups to clearly answer this but I would like to hear your explanations as to why one would be different than the or if you feel that they would be the same. Factual data is of course also welcome.

Thank you in advance.

[thebishman]

If both transmissions are identical internally re: gear ratios, etc and the only difference is in how the clutch operates, then why would there be any differences in hp/lb ft #'s on the same dyno? Besides the normal slight difference between any two vehicles?
Bish

[Arin@APR]

The R-Tronic and Manual transmissions both use a fully synchronized 6 speed transmission, which are both internally identical to one another. The only real difference between the two is the Manual has a clutch pedal, master cylinder and lines to the slave cylinder. The R-Tronic has an electro-hydraulic unit controlled by the TCU. Both Transmissions are rated to the same torque output and both use a thermostatically controlled cooling system.

Without looking too deeply into it, I would expect an R-Tronic to dyno less than a manual based on other audi auto transmissions vs manuals. However, based purely on the mechanical specs of each transmission alone, I would not expect to see a difference in drivetrain loss between the two. They internally are identical so power to the wheels should be the same between the two. I have not had a chance to dyno enough R-Tronic and 6MT vehicles, back to back, to make a scientific judgement call, but based on the the specs alone, I'm fairly confident most would not see much of a difference.

That cannot be said for other transmissions. Tiptronic transmissions (fully automatic, torque converter style transmissions) see rather large differences between Manual and Automatic. DSG on the other hand has shown, in some cases, almost no differences, however on some models there was a slight difference showing manuals making more power to the wheels. Sometimes when the difference is small, it's difficult to tell if this is due to weather or vehicle health vs mechanical design.

What should be noted is the calibration between and R-Tronic and Manual may be different. The R-Tronic may be more conservative during shifting or near redline to protect clutch engagement. Some of this can be based on the ECU calibration and some of this can be based on intervention from the TCU. With the right datalogging software, one could show the torque interventions (such alteration of timing advance) designed to reduce torque at redline to prepare for a shifting event.

What's important for people to realize is no two cars will dyno identically. Even if they are mechanically the same, and all variables are controlled as well as possible, there will be variances. Some dyno types will show variances simply due to the way the car is strapped down. If it's too tight, it may show less power. If friction between the wheels and the rollers is higher than normal, you may not see the power you expected. That's just a small glimpse into what can alter the output but it's always important to understand dyno figures are not the end all be all absolute measure of performance.

[SteveR]

If the car is not in motion and not changing gears (ie. on a dyno), I can't think of any reason they would test differently. Arin makes a good point about ECU mapping near redline. If anyone knew if that were they case, they would.

[conm]

I imagine, a hydraulic pump (used to feed the clutch actuator) is consuming a small amount of power even when not activating the clutch ie when hydraulic piston is destroked.
In any case their will be a small residual HP requirement.