markiegt3

Found this on the 992 forum. Says same stretch of road OP says, but Draggy data showed a decline, so make of it what you will. Car is a pdk 992 Touring:-

Couple data points.. only did a couple pulls with the exhaust.. it makes power. Same stretch of road, not sure why slopes are different usually its 0%. Most noticeable bump is in the mid range tq and throttle response. It lights up the tires on demand



Stock




Dundon street headers plus Ti muffler

JCviggen

Yes I've seen that one, but we need to correct slope difference of 0.57% and 684ft DA difference both in favor of the faster time. The slope correction adds 0.12 seconds and the DA is trickier but conservatively speaking 0.2s. We obviously don't know humidity and wind direction but it's not a massive difference relative to the stock time.

Anyway, I don't doubt that there are some real gains being measured by 3rd parties, the question I'm interested in is what makes the difference between gaining power or not gaining power.

The 992 setup is significantly different also both in terms of exhaust and the stock tune.

Cay_PI

992 will gain more as they have the ****ty particle filter in the oem setup.

Anyway, seems like I should visit Jens when my engine warranty is over

flsupraguy

I guess it's safe to say the "value proposition" is doing a tune only (that is if you are happy with the oem sound and not worrying about your warranty).

OR just do a dull Dundon exhaust and achieve nearly the same results. Tune plus full exhaust seem negligible?

Lolo La Torche

Concerning this car in these circumstances, the more profitable upgrade (ratio Power/Weight/easy back to stock for warranty/Price) seems to only have a pair of side mufflers deletes.

JCviggen

Yes, the value is tremendous on the tune if no warranty consideration. You can still make it loud by changing stuff post cats.

Actually on the stock ECU I see no performance jump from the Dundon headers at all. That's the problem I'm having. I was expecting an improvement perhaps half of what the tune did but I can't measure an increase - if there is one it's within the margin of error and slightly changeable conditions.

Basically, stock exhaust on stock ECU gives the same time as Dundon headers on stock ECU. Then when I flash it the time drops by 10% but remains the same whether the stock headers are on it or the Dundons. Makes no sense to me but I did a silly amount of runs and it kept producing these times.

chapmans

Possibly hitting flow limitations on the intake side?

markiegt3

Dundon claim circa 20 bhp with just the exhaust and getting on for double with their intake, so can't see that being right.

See below re an independent test and the dyno test for the exhaust was on a hot day where they feel the car would have switched map, so on a like-for-like day, they would expect it to make more power:-

https://motoiq.com/more-power-with-d...rsche-gt3rs/9/

Lolo La Torche

Should be right, and the phenomenon must be worsened by BMCs and Throttle Body modification, but on stock tune only.

The map tune should remove this limitation and a difference should be felt between the 2 exhausts, but he measured this:

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

The other hypothesis is that most of the gain is due to side silencers deletes and not really in the headers?

chapmans

I don't see how the headers don't have substantial gains just from the cat difference alone.

I would be curious to see header before after on a RS car where it already has the hotter tune, but has the better intake system

markiegt3

People say the side silencer don't make much difference and that the Porsche stock centre muffler is also pretty good.

The power should come from the headers better scavenging and better flowing Cats.............

I tried to get mine dynoed, but shop said they didn't want to mess around finding tie down points without removing undertrays.

Lolo La Torche

Yes, it should and I'm the first convinced (I bought the same headers and they are on my car for barely 10 days )

But I can't find other logical and rational explaination except the human part/ Human limits of the measure (that could be eliminated with the same test on a PDK car)

markiegt3

above video has a dyno graph from 5:35 in. Dundon catless headers tested against stock show a 55bhp increase (red graph against blue stock graph) . Conditions stated at the bottom for each test run.

Again, can vary on many factors, even how tight a car is strapped down, but should make a real difference in performance

JCviggen

Certainly not on the hardware because the tune immediately picks up a bunch of power over the stock mapping.

I agree, that was the expectation. I certainly wasn't subconsciously sabotaging things lol... I was expecting to uncover those gains that I paid for somewhere with enough testing.

I had the exact opposite experience when I modified my 718 GT4, which I also documented here on the 982 subforum. All the exhaust mods there picked up power, and the tune did very little. In fact the tune did a lot less than was promised, the stage 1 tune from M Engineering was 10 HP down on the stock ECU map when I tested it! Which made me understand that what works in the US (fuel quality and climate) doesn't necessarily work in a place where the car has an easier time making power.

The US also has a data gathering problem by sticking to simple wheel horsepower dynos which obscure what is actually going on. If you dyno a GT3 and you get 430 WHP then you assume the car was making 500 at the crank and reverse engineer the drivetrain loss to match. But you never know if it was actually making 500 at the crank, all you know is the wheel number because the loss doesn't get measured. So you don't know if it was struggling and making 480 or over performing and making 510.

Headers also have the best chance of making a positive difference in sub-optimal conditions where the stock ECU is struggling to make full power. But when things are going well there is an upper limit to how much timing it runs and how much air it lets in and the stock exhaust isn't actually terrible. Much shorter and better than on a GT4 anyway. So just the difference in pumping losses may not add up to a whole lot of freed up power. Still I was expecting more and I don't know why it's not there. I can't explain the complete lack of improvement.

Worth pointing out that my 60-130 times are overall very fast anyway. I can't find a faster 991.2 documented online, and some have done it on their .2 RS with 20 grand of Dundon stuff strapped to them, albeit in slightly slower places weather wise.

JCviggen

I would say a 55 HP difference is only possible if the car ran like **** before the mod. Again, because the dyno used is so rudimentary, you simply don't know.

edit: having looked at the video again, the stock run makes no sense. It's a Dynojet and the car didn't even make 360 stock... yes these things are all over the place for numbers but there are lots of videos of GT3s making 430 to 460 on this type. There is no way to have 115 HP of drivetrain loss on that dyno so the car wasn't running right for the baseline or the dyno itself was off. There's no cooling to speak of either, and it's a sunny day in Florida...