That is a very big spread in 1/4 mile trap speed indicating vastly different power. What is interesting is that the elapsed times are all fairly good. It is almost as if the 991 Turbo falls on its face after the 1/8 mile.
The 0-60 numbers are out of this world with Road and Track recording 2.6 seconds. 0-100 is equally impressive coming in 6.8 seconds but then the car sort of just dies registering a very quick 10.9 but only 124 miles per hour in the 1/4 mile. What's going on?
We think we have an explanation. Earlier we thought the car was pulling timing to protect the motor (a problem GM has been having with the new C7 Z06) due to heat soak and that is partially true.
Recently, a PorscheBoost member with a 991 Turbo S got his car tuned by GIAC. What is interesting to note regarding his tuning results is that the car loses 40 wheel horsepower from pull 1 to pull 3. Torque drops by 49 lb-ft in that same span:
Keep in mind this is on a conservative reading Mustang dyno. On a Dynojet someone would be looking at over 50+ wheel horsepower lost. That is massive.
Now once this was posted PorscheBoost started getting info from various sources who wish to remain discreet to not upset GIAC. The truth is, GIAC knows the car is pulling boost and timing. As does Champion Motorsports who is readying an intercooler upgrade for the car.
The vehicle is attempting to protect itself when heat soaked and it appears to easily get heat soaked. Some tuners swear the 991 intercooler and cooling is great but how do you explain such a large drop in torque from pull to pull and the car pulling boost as it heats up?
The owner who got this tune dyno'd has run his car at runways events and from the first run to subsequent runs he lost 6+ miles per hour of trap speed. The dyno runs and inconsistent magazine figures support all of this.
The GIAC Stage 2 flash is forced to pull boost at high rpm's to prevent limp mode. The stock car is already pulling boost and timing itself. Tuning just exacerbates this problem.
We will see how tunes are revised and what cooling solutions Champion Motorsports comes up with but clearly the 991 Turbo is not a consistent performer especially when tuned as of right now.