How much hp is gained/loss with a 30 degree F difference in temperature? My best run in 50degF temp was 15.51 @ 85.88 mph. After installing the Borla cat-back my best run in 80degF temp was 15.53 @ 86.54 mph. I was also powershifting in the run with the exhaust installed so that might contribute to the higher trap speed. How significant of a factor is temperature?

...and 30 degrees of temperature might cost you half the HP you gain with an exhaust. Compare your 60' times for the 2 runs. Your 15.53 run with the exhaust may have had a slower 60' time, meaning you just didn't launch as well, but then ran faster over the next 1260' to have nearly the same ET (at least you got an extra 0.66mph through the traps).

MPH= HP
ET= Trq and skill.

Forget the ET. Look at your MPH.

If you ran faster in hotter temps.


It works.

Clark

30 degrees on a normally aspirated car equates to a loss of about 4% in power, partially compensated for by lower drivetrain friction and lower rolling resistance. However, on a turbo car, you'll lose at least 5% or slightly more. See SAE Standard #J1349 for the particulars. Powershifting a turbo car can lead to substantial improvements over normal shifting, however, so the key question is: Did you make any passes after the exhaust change *without* powershifting? If so, what were the results?

PS - Figure the quarter mile speed and ET change based on the cube root of the power-to-weight change. Your mph change indicates a gain of 2.3% in power, not accounting for the powershifting.

Humidity and barometer also affect power, by the way. Do you happen to have those numbers?

still you went faster in the 80 degree heat!

Hey man, I saw you run that night at the Atlanta Dragway in Commerce. Your car looks good bro. I saw you run a 15.7. My GTi VR6 with chip, intake and exhaust ran a best 15.8 at 88mph. I KNOW my car should be running low 15's, high 14's. Did you see me run that night? I remember coming up to you just as you were about to run that night.. Sweet car.

- Charles
quickgti@aol.com

I could send you the clip if you want. You had the black GTi with the blue taillights, right?

Hello,

Quick calculation here, so bear with me. The ideal gas law PV=nRT (yes, my students cringe too!) Assuming no changes in atmospheric pressure, P,(we will assume 1atm or 1bar, sea level) and 1.8 Liters, V, of engine displacement (could assume this to be anything as we are looking for percentages here), the number of moles, n, (Avagadros # of molecules) in this amount of air at two temperatures 30 degrees Farenheit apart (I used 80F=26.67C=299.67K and 50F=10C=283K:

At 80F
1atm * 1.8L = n * (0.0821 L.atm/mol K) 299.67K
n=0.0732 moles of air

At 50F
1atm * 1.8L = n * (0.0821 L atm/mol K) 283K
n=0.0775 moles of air

So, with only changing temperature on a NA motor (don't have the data to figure in what the turbo does to all of this) you will only make 94.5% as much power (assuming complete efficiency and power is directly proportional to air intake) at 80F than you do at 50F.

Again, Im at work and this is a quick calculation and perhaps an oversimplification, but does point to a 5% difference in available power.

Also, the engine computer may need some time to catch up with the new parameters created by your new exhaust.

Let us know if you can get a better time at the same temp!

Cheers!

Michael

hopefully it'll free up some of the extra power from the exhaust.