Hey all, as my first post here I'd thought I'd start off with a quick pic of one of my cars and something that may be of interest to the GT3 owners here. Some of you may know me for my work on chipping and retuning 911s over the years. After I completed a live remap/rechip of a 3.2 with a mass flow conversion, the Dwain Dement and guys at Vision Motorsports in Laguna Hills, CA were kind enough to put the GT3 on their Dynojet to get a power and AFR read. I can't say enough about their experience and detail in dealing with these cars. They race and service many GT2, 3s, and cup cars of their own and for several clients. As part of the routine for preparing the GT3 for the dyno, they remove the lower body panels to properly strap down the car so as to not damage the body or suspension components. The ABS module was disconnected to prevent the car from going wack. A couple of runs were done from ~2000 till the rev limiter hit at 8300 rpm, with the results shown below. Result: 370 RWHP at 7600 RPM, peak torque of 270 ft.-lbs at 5500 rpm. Assuming a 15% drivetrain loss, engine hp calculates to 435 HP / 317 ft-lbs torque at the engine. What is especially notable, is the textbook perfect fuel mapping throughout the entire rpm range, with a AFR of 13.0:1 +/- 0.2, with a slight richening of the AFR at peak torque to about 12.6:1. You just can't map the car any better than this. I believe though there may be an additional 18 lbs of torque in the 3000-4000 rpm that the dyno doesn't show because apparently you cannot engage the exhaust sport mode due to the ABS system flagging.

After completing the runs, Vision carefully reinstalled all the panels, reconnected the ABS module, and with the PIWIS tester, cleared all flags in the system as a result of the runs.

What was interesting is Vision had dyno'd a 997 GT3 Cup car about two weeks prior, and although that car also made the same 370 RWHP at ~7700 rpm, when overlaying the dyno runs, the overall power curve was 35-40 hp less throughout the entire rpm range. This I have seen before as I have seen some odd dyno runs from 997 GT3s in my database.

Steve

 

this is a stock 997 GT3, right?
anyone have dyno graph from 996 GT3 as comparison?

 

Very good result if it's a stock car.

 

Hej there

I belive its quite an amasing result for a - genuine stock car.. In europe we run 99 oktane on it - what kind of fuel do you run ??

Regards from Scandinavia

 

Where did you come up with the 15% loss number to calculate crank HP?

 

Nice- good stuff Steve.

The 997 Cup is missing the variocam, so I'm guessing that's probably what caused the big hole through the midrange vs the 997 street. I didn't know you'd done GT3s. We should probably chat- I've got a "special project" 997 cup with exhaust, etc that could use some help here shortly, maybe Tyson/ Hayden have mentioned it...

-Pete

 

these cars are so efficient at putting the power to the wheels. i have always thought they put it down better than every other car other there.

 

Great result. I had a 2000 996 gt3 mark 1 clubsport about 4 years ago with an exhaust and powerchip. Dyno'd twice. One was 311hp at the wheels and the other 222kw at the wheels - on different dynos. Had a friend with an identical 996 Gt3 and was with .25kw of mine on the same day so is about right. No wonder the Gt3 lap times have dropped so much over the last 5 years.

 

The engine and exhaust is completely stock and was dyno'd on 91 octane California pump gas. The 15% loss factor is we've found to be a typical loss factor through the wheels and transmission from years of dynoing many 911s of various years and configurations. Some of the 911 engines have been dynoed on an engine dyno such as a Superflow engine dyno, and many 911s have been dynoed on Dynojet and Mustang chassis dynos in comparison.

As for the missing torque between 3-4200 rpm, it is likely because the system is not allowing the exhaust sport mode to activate. Because on a 2WD dyno, the front wheels are not turning in sync with the rears, the ABS and Traction Control system deactivates the sport mode. If you look in the factory specs, with the sport mode engaged, the engine produces an additional 20-25 NM of torque right in that range. If you overlay the factory dyno charts with the one above, you can see exactly where the missing torque is. I haven't discussed any of this with Hayden or Tyson, however Hayden tells me they are working on some crazy project for a client: retrofitting an entire GT3 motor into a 356 chassis.

I don't have a stock 996 street GT3 dyno file on hand, but here is one from a '99 GT3 Cup car, with an aftermarket exhaust system:

 

WOw! That a great result. Very efficient car.

 

Very impressive but theres always room for a bit more!

 

Thats a interesting dyno

 

Did you align your center caps for that last pic?

 

Pretty close. Right motor, wrong early car...
I like the curve on that '99 cup with the exhaust. Mine's an '06, which starts out with a few more stock, so that's quite promising. One thing though- I'm running the Bosch Motorsports ECU. Is that in your bag of tricks?

 

Yes, the GT3 is a very efficient motor, and at 115-120 hp/liter, is at the end of what Porsche can attain from the GT1 crankcase. Yeah, Porsche could go to a 3.8, but the cylinder walls become very thin, and if they went to a longer stroke, the motor probably wouldn't wind out too well, thus why I think they had to go to a new crankcase so they could break the 500 hp normally aspirated barrier for future motors.

Dave very observant. The wheels had just been serviced for the pressure monitors, so the caps were put in for the pic afterwards.

The dyno is a Dynojet 248x, mounted above ground, so it may not be recognizable to some. Here's a clearer shot of the wheels on the drum.



As for tweaking for more power, we'll see. Half of typical power optimization is correcting and optimizing the air/fuel ratios of factory programming, however I believe the factory dyno's and custom maps each GT3 motor to optimize the AFRs and there's nothing left here to optimize. The remaining gains come from increases in ignition timing, and as the GT3 already specs and requires 98 RON, or 93-94 CLC octane fuel, and California only provides 91 CLC octane, I'm not really sure there is much additional power to gain other than tweaks for throttle response and such. Revised headers with cat bypasses may further increase power, but that is beyond what I want to do now.

I thought you might all get a kick out of a comparison of most of all the past Porsche motors and see how they compare to cars of today. I've compiled some of the more popular 911s in the chart below compared to the GT3:



The above chart are 911s dyno'd on a Dynojet 248. As follows:
dark green: 2.4 MFI
teal blue: 3.2 Carrera, chipped
red: 964 3.6
bright green: 993 3.6
brown: 2003 996 3.6
pink: 997S 3.8
blue: GT3

The above chart makes a GT3 look impressive, until you look at the comparisons to twin turbos and the newer cars below:



In the above chart, also on a Dynojet 248x:

Green: Cayman S
Pink: 997 GT3 Cup
Dark Blue: 997 GT3 street
Red: 997 twin turbo
Purple: 997 GT2
Teal blue: 993 twin turbo 25 psi

All of the above being HP at the wheels. Divide by 0.85 to estimate hp at the crank.