Decided to dyno my stock 997 Carrera GTS 6MT today to attempt to get a baseline reading. The dyno was a 2wd dynojet. First problem was being able to find a tach pickup. Coil pack was too hard to get to, tried the ECU harness in the back seat but no signal still. Gave up and just went with power vs. mph with no rpm but at least there was an AFR sniffer in the tailpipe.

Tried 2 pulls, PSM turned off, spoiler up and about 50F ambient temp. 1st pull (red) only ran until around 7000rpm while the 2nd pull (blue) ran up to 7400rpm or so, both done in 5th gear starting at around 3000rpm. I was aware there may be problems dynoing on a 2wd dyno since the computer would get confused since the front wheels weren't moving but I figured this would just be some errors thrown, which did happen such as the ABS/PSM error and the CEL. ABS/PSM error cleared within a few seconds of driving, the CEL cleared after a few restarts of the car and some driving. One thing my friend and I did notice was there was some smell of brake pads during the runs, but the rotors were cool when we touched them right after to check.

Some things the dyno operator noticed - AFR leans out during the pull (>14) then richens up during the "ramp" up near the last 1000rpm (between 125 and 145mph on this graph). Shape of the curve itself looks strange like something was off and total power is lower than what would be expected with typical drivetrain losses factored in.

Any help shedding some light on this odd dyno would be helpful. Should I find an AWD mechanically linked mustang dyno and try again?

Thanks!

 

Here is my readings on a AWD that I did about 2 years ago.

You should use an AWD to get a true reading.

 

You wanted a baseline and now you have one. 330 hp at the rear wheels but you think it should be higher. Why? Seems reasonable to me. A different machine might give a higher or lower #. Is there someone out there that has gotten significantly higher readings on the same machine under the same conditions? Personally I think you are right where you should be with this. Drive it and enjoy the ride. They are nice cars.

 

I have spent plenty of time on a dyno. You car looks good, you got a base line on it, and plenty strong for sure. The rich arf is normal on a factory ecu. I tuned my car at 12.7 wide open , and picked up 10 hp across the board, stock afr was 12.2.

 

With the car stationary there's no air flow or positive air pressure over the engine compartment. This could result in the engine breathing in less air than it would if were running down the road and could account for some less than expected HP.

I hope dynoing the car on a 2WD dyno didn't fry the front drive clutch pack. I think that is what you were smelling.

This probably accounts for some loss of HP at the rear wheels, too.

 

I believe GTS to be rear wheel drive. Anyone?

 

Yes, GTS rear wheel drive with higher HP and the wider rear hips.

They did make a GTS 4 though, which would be all wheel drive.

 

Hi all, thanks for the input. The car is RWD, supposed to make 408 crank HP so even with 15% drivetrain loss that should work out to around 345whp or so. I guess its close, but what I'm more worried about is the AFR and the shape of the power curve. The AFR leans out to about 14.5 midway through, then looks like its running out of breath. Then all of a sudden it richens up to 12 almost and makes more power to redline. All of the 9A1 dynos I've seen don't exhibit this shape - it's quite linear to the power peak then it slowly tapers off and the AFRs are usually sub 14 the whole way through when WOT.

A friend dyno'd their M3 just before me and their whp numbers were in line with a 15% loss from claimed crank hp so I don't think the dyno reads abnormally low. There was a fan set up in the front of the car so there was some airflow at least, but not as much going to the rear I suppose. I talked to some tuners and they mentioned that these cars don't like dynoing on a 2WD dyno since the front wheels not moving causes the car to possibly run in a different "mode" for safety reasons. They recommend using a mechanically linked AWD mustang dyno even for RWD 997's to get the most accurate result as RaidersR1 also mentioned.

 

When I did my Dyno run there were AWD's and 2 WD models there as well as a very tuned M3. None of the 2WD used the AWD testing on the dyno and they ran just great.

The tester did but two fans in front of the car and two at the rear of the car to give air flow to the engine compartment. You mention running the car in 5th gear. I'm surprised at that because during my dyno run, my car was never taken passed 2nd gear. I'm no expert but it appears to me that the best gauge of the HP would be 1st and 2nd gear runs to lay the power down quicker. Watching my car on the dyno the tester took first gear to the max before letting off the throttle.

Others can chime in about this as well.

 

My car was ran on a 2 wheel dyno, and the car performed as expected. We ran the car in third gear from 2k rpms all the way up to redline. I honestly think that are a lot ways to get a reading. All dynos will read a different number, nature of the beast.
By changing timming the fuel curve , you can clean up the power delivery. these engine tend to have a dip in power at 5000-5500rpm, experts say its caused by the over exhaust scavenged in the engine, and can't be tunned out.

 

RWD it is then. For some reason I had it as an AWD vehicle.

 

Never dyno'd any of my cars but I attended a few dyno sessions. SOP was to use 4th gear which back then was 1:1.

4th or 5th gear -- which ever one was closest to 1:1 with the gear ratio being a bit over 1:1 vs. a bit under preferable -- would be best.

With Corvettes and their IRS a problem was often the dyno operator really cinched the car down. This is understandable as no ones a car to come loose on the dyno rollers. But if the rear is pulled down too much and the half shafts are not parallel to "road surface" this costs HP as the CV joints eat some HP.

 

OP's mention of 4wd dyno confused the issue.