Inrev

I'm not used to seeing such impressive bolt-on gains on NA Porsche engines, good job!

trebien

Going to switch membership over to Kidney4sale.com?

Jamie -

Interesting information. Was this run with a NEW tune for this TB/Plenum situation, or your standard "header" tune?

Do you feel that this is likely because the added possible flow benefits of TB/Plenum (which would probably be upper RPM range) are still bottlenecked by the OEM exhaust? Or is there something else at play?

I'm curious, because really wish to know how limiting the OEM cat-back exhaust has for upper RPM gains... it would nice to be able to keep it if the bottleneck was minimal, but as parts were added.

Jamie@dundonmotorsports

This is the wonderful benefit of using the Porsche Sport Exhaust, no drone at all, sounds great at low rpm cruise, can talk in the car without issue!

We bolted the TB/Plenum on with our headers and our developed tune. We logged the car and didn't see a noticeable gain. We flashed the car to stock and same story. We also logged manifold pressure, which surprisingly on the GT4 is sub ambient at WOT, this typically indicates a restriction as not all the air the car is asking for is filling up the manifold. The MAP was the same for both the setups. We're not sure why this is, but we know that the race headers are pulling quite a bit out of the cylinders in order to get 43whp at 7500 rpm. We believe this is all resonance wave governed, and it's possible that our race system is too strong an influence to see a difference with the TB/Plenum mods. we will continue to do more research and testing on this, but wanted to get the system out ASAP. The Good news is we're making a lot of power for just bolt on headers and a tune, so less parts to buy and less money to spend on installation. We have a few variants of plenum coming (all Porsche factory parts). And also will be 3d scanning the entire intake system as we would love to see the MAP a bit close to ambient (there is a ram air effect with these cars as well, but more on that later...).

We've run the car with a complete straight pipe exhaust during our testing and there was a bit of a benefit at high rpm. We will be offering this along with the street catted system once complete!

Jamie@dundonmotorsports

991 GT3 was the record holder at 40whp, now the GT4 is at 41whp!

DrJay

This is with nothing but headers and a tune?

Jamie@dundonmotorsports

Yes!

trebien

Also in line with my thoughts. This vehicle has some interesting resonance effects, especially if a straight pipe exhaust is doing little. We all know Porsche does a lot of resonance wave testing AND design implementations. At least you have the 991 Carrera S X51 vehicle to give you some clues, likely a path you're headed down.

The ram air might help a little, but your negative manifold pressures gives some clues as well regarding the entire airflow environment, intake to exhaust. I would doubt the manifold stays negative at speed due to airflow... but who knows.

Great info.

Knolow

Slow clap. Headers/tune had me once I saw above 370 whp, let's talk straight pipe!!!

Jamie@dundonmotorsports

That's all modular, so get the race headers and our exhaust section will bolt right to it when finished! That's all part of the catted development!

user1029

I'm pretty sure I have only one kidney after waking up in a tub of ice in Thailand circa 2001.

Alan C.

And it's still working for my client.

user1029

Accel Junky

Great gains of course...but I think I'm priced out of these. It was a fun thought while it lasted. That's a lot of track days worth of $$$.

d00d

I didn't calculate each RPM from the BGB thread graph, and I assume tune cost is the same, but is the roughly 10whp difference at 6500 RPM worth ~$1,720?
It is to me.
Made in the US, 321SS, and possibly improvements to the tune for plenum and TB to come.

Dundon race headers $3,750 and free shipping group buy, tune;
3600 RPM: +50 wtq +32whp
5000 RPM: +55 wtq, +52whp
5800 RPM: +24 wtq, +26whp
6500 RPM: +30 wtq, +36whp
7500 RPM: +30 wtq, +43whp

Cargraphic race headers $1,980 plus half off shipping ($50?) group buy, tune, filters, plenum, TB;
342 - 316 = 26whp @ 6500
https://rennlist.com/forums/gt4/8822...l#post12683867

ShakeNBake

It's pretty obvious from the very lumpy torque curve that the GT4 has a lot of resonance tuning to make up for breathing issues.