Finally Went To The Dyno!

[IFLYASA]

Well I did my first dyno today. I have a 99 model C2 911 with 42,500 miles. I have done 3 mods. I have the fabspeed intake, fabspeed exhaust, and JVT headers.

I drove about an hour to the dyno shop so naturally the porsche was hot. The best of my first two runs were 256.0HP at the wheels, with 222.3 ftlbs of torque. After letting the engine cool down with some fans, I did a third test. This yielded 262.9HP at the wheels and 233.5 ftlbs of torque. The temperature was just over 80 degrees. Now assuming a standard day of 58 degrees, I'm sure the results would have been higher.

Anyway, I was trying to caculcate the HP at the crank. I hear 15% loss is par. I did not have any stock 996's to compare with on this exact dynojet. So I looked at 2 graphs of 2 stock 1997 993's that were tested on the paticular dyno. They were both right at 236 HP at the wheels. A stock 993 produces 282HP at the crank. This yields at 17% efficiency drop on this dynojet. Using this for my car, gives me roughly 317 HP at the crank , and 281 ftlbs of torque, at 80 degrees outside temp. Using 15% efficiency drop would yield 309.5 HP at the crank, and 275 ftlbs of torque.

In summary my HP over the stock numbers was around 13.5 to 21 HP peak gain, and 19 to 25 ftlbs peak torque gain. I'm curious what the numbers would be with a 20 degree temp drop. I may go back in early winter and retry. Here is a graph of the dyno:

Edited October 10, 2007 by IFLYASA

[1999Porsche911]

A typical dyno (if you MUST believe that they are accurate) shows 252 rwhp on a 99 C2 6speed. And, NO, your dyno would not have been higher on a cooler day if both the operator and the "theory" behind a dyno were accurate. Variables in temps, pressure, altitude, etc, are all adjusted for to provide for consistant results.

So 252 RWHP versus a reported BHP of 296. That assumes that you can believe either of those numbers. RW torque is 218.

Edited October 8, 2007 by 1999Porsche911

[IFLYASA]

A typical dyno (if you MUST believe that they are accurate) shows 252 rwhp on a 99 C2 6speed. And, NO, your dyno would not have been higher on a cooler day if both the operator and the "theory" behind a dyno were accurate. Variables in temps, pressure, altitude, etc, are all adjusted for to provide for consistant results.

So 252 RWHP versus a reported BHP of 296. That assumes that you can believe either of those numbers. RW torque is 218.

The operator was on his computer doing his thing. I know after two runs after driving an hour in the heat, the numbers were consistently 7HP lower. After it sat for 15 minutes with fans blowing on the engine, and radiators up front, that's when I got the better result.

Well that sounds about right. 262.9hp vs 252hp, and 233.5 torque vs 218. Headers, Fabspeed exhaust, and Fabspeed intake is probably the difference. Anyone know why the drop of HP around 5300 RPM, and the spike back up at shortly after? The 993 stock dyno I saw pretty much did the same thing at a different RPM.

[1999Porsche911]

A typical dyno (if you MUST believe that they are accurate) shows 252 rwhp on a 99 C2 6speed. And, NO, your dyno would not have been higher on a cooler day if both the operator and the "theory" behind a dyno were accurate. Variables in temps, pressure, altitude, etc, are all adjusted for to provide for consistant results.

So 252 RWHP versus a reported BHP of 296. That assumes that you can believe either of those numbers. RW torque is 218.

The operator was on his computer doing his thing. I know after two runs after driving an hour in the heat, the numbers were consistently 7HP lower. After it sat for 15 minutes with fans blowing on the engine, and radiators up front, that's when I got the better result.

Well that sounds about right. 262.9hp vs 252hp, and 233.5 torque vs 218. Headers, Fabspeed exhaust, and Fabspeed intake is probably the difference. Anyone know why the drop of HP around 5300 RPM, and the spike back up at shortly after? The 993 stock dyno I saw pretty much did the same thing at a different RPM.

The drop in power is the resonance valve opening up on the second crossover intake tube.

[IFLYASA]

I talked the dyno operator about temperature. Here was his reply.

" The dyno used the SAE correction which corrects to STP, standard temperature and pressure. Standard temp is 70F. I don't know the pressure. Even with the correction factor, cars will usually make a little more power in cold weather."

FYI

[1999Porsche911]

I talked the dyno operator about temperature. Here was his reply.

" The dyno used the SAE correction which corrects to STP, standard temperature and pressure. Standard temp is 70F. I don't know the pressure. Even with the correction factor, cars will usually make a little more power in cold weather."

FYI

And THAT is exactly why numbers produced by a dyno have no credibility. (except for keyboard racers). :)

[Izzy]

IFLYASA,

thanks for going through the trouble of putting it up and sharing, I know the dyno runs are not free. Do you recall what the Fabspeed site claims as HP increase? This may be an interesting validation.

I have similar cold air intake mod and GHL mufflers.

[IFLYASA]

IFLYASA,

thanks for going through the trouble of putting it up and sharing, I know the dyno runs are not free. Do you recall what the Fabspeed site claims as HP increase? This may be an interesting validation.

I have similar cold air intake mod and GHL mufflers.

Funny you should ask. I just emailed them about their dyno. If you go to the fabspeed website, look under 996, and then the Fabspeed exhaust, it showed a stock run of 218.2 hp, and then 234.7 ftlbs after the exhaust. (Awfully low, must be a weird dyno). This would be a 16.5 hp gain and 8.7 ftlbs of torque. But in their adertisement, they claim 8-12 hp gain with 10 ftlbs of torque. I believe the 8-12 to be right.

I also have the Fabspeed intake and JVT headers. Since I never did a base line run, I assumed 252 factory hp with 218 ftlbs of torque at the wheels. My results were 10.9 hp and 15.5 ftlbs of torque at the wheels. But then again, dyno's are different. I WISHED I had done a factory run long before my mods to know the true gains.

Remember this is peak horspower and torque gains. There could be higher or less gains thru the curve. I'll let you know what fabspeed says.

Edited October 10, 2007 by IFLYASA

[Izzy]

Thanks, I think relative values are very useful, even though they are not absolute or exact. Again, thank you for doing all of these and sharing with us!