Jamie@dundonmotorsports

Just a heads up, we have 4 sets of GT4 Race headers in stock for anyone who was on the fence or didn't want to wait! Just finished and the first time in a while we're not back ordered on them!

321 Stainless
Dundon Exclusive 4th Tube
Fully purged TIG welded construction
Lifetime warranty including track use
30 day money back guarantee
Set of K&N High Flow Air Filters Included
All Hardware including studs, nuts, springs, gaskets, tools included.

https://www.dundonmotorsports.com/po...425hp?carid=41

4 sets ready to go for $3950/set!



Gains:
3600 RPM: +42 wtq
5000 RPM: +36 wtq, +34whp
5800 RPM: +15 wtq, +16whp
6500 RPM: +28whp
7000 RPM: +30whp
7500 RPM: +41whp



Intake Temps at 60F (above 20C/68F ECU starts to torque limit for emissions).

IPSA

Why do there appear to be 4 tubes coming out of the collector?

chillindrdude

One of them is just blocked off. Maybe functioning as a heimholz resonator?

lovetoturn

Yes, the heimholz resonator affect of the extra tube is what can get rid of the notorious drone noted in our exhausts. It can be cut to a specific length to cancel out particular resonance frequencies in the exhaust. This makes it quieter. It may also give a bit more power, but that is a question for Jaime.

ajw45

Just wrapped up another track event with the DMS headers! The only way to go for power, quality, and no CEL!

benben01

yup yup... I can attest that the DMS headers have very little if any drone..

guab

Love my Dundon race headers!

Alan C.

Great addition to my GT4. I have over 10,000 miles on my Dundon headers with no CEL or drone..

CME

Added the Dundon headers, air filters and a Cobb tune earlier this year.

James88

Gains:
3600 RPM: +42 wtq
5000 RPM: +36 wtq, +34whp
5800 RPM: +15 wtq, +16whp
6500 RPM: +28whp
7000 RPM: +30whp
7500 RPM: +41whp

Wow !! that is a pretty significant power boost with just headers. Would this be fairly accurate with all GT4's in any continent, I'm in Australia and on the local 98 octane fuel ?

Jamie@dundonmotorsports

It is blocked off, but not as a helmholtz resonator.

The lack of drone is due to the muffler design and the valves that switch the path from a longer to shorter one (just like the 991/997)

AJW45 is also testing our Quiet GT3 muffler...


Glad you're all enjoying them! I agree the headers truly transform the car.

And this is why the 4th tube. Power throughout the rev range. A couple things to consider here.


The assumptions are that stock headers don't flow enough air and that making them a larger diameter or removing the cat alone would yield big power gains through a reduction in resistance to flow (or back pressure).

A GT4 doesn’t have much resistance to flow, so removing the cats or increasing the size of the tubing doesn’t yield much horsepower.

An engine exhaust isn’t a fan (unless it’s turbo charged and that’s a different discussion) it’s a bunch of well timed gun shots. The pressure waves from the exhaust valve opening bounce around in the primary tube. The length and diameter you make the tube dictates when and how strong that reflected pressure wave (now a “ vacuum” wave) makes it back to the exhaust valve. If you time the reflected wave correctly you get the maximum vacuum wave to occur during intake valve and exhaust valve overlap and you’re able to suck more exhaust out of the cylinder and create a vacuum in the cylinder that sucks more air than atmospheric pressure will push into the cylinder through the intake valve. The 4th tube aids in the strength and timing of the pressure waves. This is how 40whp gains on a “non restrictive” exhaust


Why doesn’t the OEM do this? Well they’re trying to keep exhaust gasses trapped and burn Them over and over to reduce NOx emissions (Called exhaust gas retention or recirculation). They design the exhaust to keep the waves from getting there at the time that would produce more power, they want them to push the exhaust gasses back into the cylinder to some extent.


So by understanding the pressure waves, doing the math and building a well designed product your able to use the entire volume of the cylinder and actually super charge it a little.

Okwute

This is strictly for tracked cars and not for street only cars. correct?

James88

Thanks for the in depth explanation Jamie. Would there be much difference with factory Air Filters and not using K&N High Flow ?

This is very temping, my only concern is it might affect warranty.

O5C4R

Hi James I got the first and probably only set of these here in straya, Porsche didn't question them at all when fixing the 3rd gear issue under warranty, there was some questions about wtf the 4th tube does
be prepared for the sound over 4k rpm

James88

Interesting not questioning, might be a little different at Porsche Melbourne, after all they're Porsche Australia head office and go by the book.
Haha.... is it that loud, any added drone ???

Did you have your's dyno'd ? Can you really feel the difference in extra power ?