Dyno Results

Below details my first pull on a dynomometer. The second round of dyno testing revealed marginal gains. Not much to mention here.

I've been feeling what I describe as a torque ramp around 4 krpm. I figured it was just coming on cam but the helpful folks on the PorscheFans 928 mailing list insisted something was wrong. A couple of months after I bought the car a friend was taking his '96 Camaro SS (hi, Bryan!) to AutoTek here in Austin for a couple of pulls on their chassis dynamometer. I had decided to do this already so I jumped at the chance to compare the Porsche to a car very much like my Firehawk under the exact same conditions.

AutoTek's dyno is a Dynojet Model 248E Chassis Dynamometer. Results are taken at the rear wheels and corrected to SAE standard conditions. Take a look at the results for all the detail. I also have a scan of the printed results if you haven't filled your IP bandwidth already. If I'd been thinking of it I would have had the operator start at 2 krpm. Oh well, maybe next time.

This clearly shows my torque dropout (that ugly V-shape) between 3200 and 4000 rpm. Power is flat there and really starts to take off after the trough. Peaks are 303 lb-ft @ a low low 3200 rpm and 277 hp @ 5700 rpm. Power really doesn't drop off much well into the redline. Of course, anybody who drives this car can tell you that. :-) The suspected culprit is a bad sensor causing the computer to retard the timing.

As it turns out, the variable runner length flap in my upper intake was sticking. The late opening was exaggerating this torque dropout that seems to be a fact of the factory tuning. Many shark chums report favorable gains in this area using aftermarket PROMs ("chips") so that may be my future direction. That is if I can find a set considerably cheaper than their ridiculously inflated prices.

The approximate powertrain loss on this car seems to fall around the average 15% rule of thumb (~17% for automatics). Given 277 at the wheels, that would give me about 325 hp at the flywheel which is in line with the factory specs.