74goldtarga

I looked at the dyno plot on the COBB website and their gains on 93 octane / 98 RON tunes are more significant for the 991.2 than the 991.1 which doesn’t surprise me. It would also not surprise me if the gains on the 992.1 were less and that the state of tune from the factory was higher. Logically, the 991.2 GT3 should have the most to gain from tuning.

If some of the gain is from better fueling depending on altitude and temperature/air-density then I should be able to reap gains here - we
do some cold trackdays.

JCviggen

FINAL testing done with the Dundon street headers on stock and tuned ECU.

DA was slightly better than before the Dundons went on but the same problem of very high humidity remains so performance isn't as good as it could be - it actually seemed very marginally worse for performance than Friday even with the DA technically lower.

I did a lot of runs, about 30 in total. I drove the car, I went through tanks of gas and there was always plenty of time for the car to "adapt". There is no wind factor, the stretch I use had a light breeze at a 90 degree angle to it.

So I can sum up the 60-130 data as follows:

1) Stock exhaust except for side deletes, DA 1000ft slope +0.07: 8.96s
2) Dundon street headers, stock muffler, DA 700ft slope -0.04: 8.84s
3) Stock exhaust as above but with tune, DA 1000ft slope +0.12: 8.08s
4) Dundon setup as above but with tune, DA 700ft slope -0.03: 8.09s

I tried, I really tried, but the car does not want to go any faster with the Dundon headers on it. And I went into this convinced that there should be several tenths to be gained but the data proved me wrong. I did do a 7.98s 60-130 in the end but the slope was -0.37 so it corrects back to just over 8 secs. Anyway you can't stare at a couple of hundredths of a second because it's a manual car and there is a very slight variance in my shifting (+/- 0.05s)

The ECU flash however creates a huge jump in noticeable power and torque. It also gives full power in 1st and 2nd gear where I felt the stock ECU was holding back a bit, possibly this is manual specific programming that is not present in PDK cars but 2nd gear always felt a bit "wavy" in terms of power band. After the tune it pulls straight and solid, and harder.

I plan to do a Spa trackday with the headers on in April, if they throw me off the track for noise (I do have a set of Nurburgring quiet tips) I'll go back to stock headers with the side deletes as that seems to be a very nice solution and 11.5lbs lighter.

DDE997

This is Great info. The stock tune in the GT engines is held back some. I am going to run my .1 of 100% e85 soon.

flsupraguy

can't wait to see how it does on e85

JCviggen

Hope you have the extended fuel tank Keep us posted!

After combing through all of the data, focusing only on runs that started in 3rd with 1 shift to reduce variance and correcting for slope I think I found a possible small gain for the Dundon headers. It's in the order of about 5-6 horsepower and 0.1ish second advantage. Maybe. You can just about measure it (easier on a dyno) but not feel it.

markiegt3

Interesting JC.

I wonder if there is a longer adaptation time for the Dundon system?? A hassle I know, but I wonder if you can find the time after the system has been on and you have suitably ragged the car to run another 60-130 with or without the tune?

I am hoping you find a few tenths, as the owner of the Dundon system!! Certainly feel quicker in the low/mid range, but doubt that help with the 60-130 runs.

Cheers,

Mark

JCviggen

If several hours of running time, several restarts and doing enough pulls to empty a nearly full tank of fuel didn't make it adapt then I don't know what would. ECU adaption is often overstated. After a couple of full throttle pulls it knows what it's doing. If the car suddenly feels "faster" a week later you probably woke up on a day with favorable atmospheric conditions...

Lolo La Torche

Maybe the manual gear shift process could vary from a test to another one?

It should be interesting to make the same tests with aftermarket air filters and see if there is a better combination of inlet/exhaust?

JCviggen

I have the shifting down to a science nearly, very little variance and I did a lot of pulls from 3rd which is just 1 shift 3 to 4 which is easy and consistent. Plus the 60-100 mph times show the same thing and there is no shifting involved.

I have the BMC air filters and a slightly upgraded throttle body, but those are not required for exhaust side gains. After all the ecu tune has no problem adding 35HP on the same hardware.

Lolo La Torche

So, it should mean that you’ve reached the limits of stock ÉCU.

Maybe the results on the dyno were deceived by the lower amount of air absorbed by the car in these conditions, compared with a dynamic driving that feeds the engine much better in fresh air...

So, on the Dyno, the car is probably more far from the OEM maps limits and is able to increase power with better exhaust.

Perhaps all my recent invests were not so profitable as I thought…

JCviggen

I would understand if there was not much power gain from the headers when running the ECU tune. After all, there is only so much power you can make so there are diminishing returns. But then on the stock ECU there's not really a difference either 🤔

Please do your own testing and report back 👍

Lolo La Torche

I’ll try, but it’s not easy at all for me to make such measures and tests

What throttle body mod did you do?

markiegt3

https://motoiq.com/watch-porsche-gt3...antee-eargasm/

Dyno results for 991.1 gt3 rs & graph at the end of the video

Supposed to be better overall with no dips for the 991.2 gt3???????

flsupraguy

It's odd many people experience noticeable gains with dundon headers (even on stock tune) but the OP hasn't (or hardly hasnt). Perhaps the the headers "lean out" the orm tune so tune and headers together yield minimal results?

markiegt3

Yes, but tested with standard tune too and didn't make much difference??

JC did follow up saying he felt they did give a small improvement, but the claimed 20-25bhp atw should give maybe 0.5 second improvement??

All the header manufacturers claim 15bhp plus more, JCR, Akra, GMG, Fabspeed etc, so a bit baffling!!!