[Cunningr]

Originally Posted by 10/10ths

...the critical part of exhaust flow is immediately upon exiting the exhaust valve. Long tube headers with no cats allows the exhaust to QUICKLY get outta the combustion chamber and if tuned properly helps “scavenging” that allows intake flow to be better in addition to exhaust flow.

The exhaust gas cools very quickly and slows down as it cools due to the laws of thermodynamics. This is why cats that are further downstream don’t have as big a detrimental affect on exhaust flow.

The stock muffler actually works really well and the car NEEDS either the original muffler or a high quality copy of similar shape and mass because the entire drivetrain WITH the muffler was balanced and tuned by Porsche to act as a mass balancer of sorts for the entire vehicle. Only a big single can will prevent the horrible drone on the highway in top gear.

The FVD Brombacher “Sound Version” muffler is very expensive, but it is built out of T316 stainless, a much higher quality of steel then even the OEM muffler, provides a great sound, will stay shiny for life, and will never burn out. That is the best option for a real world, street driven car.

If you don’t care about cross-country driving without a headache, then buy any muffler you want.

The high flow cats in a quality secondary pipe won’t affect your power output much. For a street car, you really should run them if you use long tube, catless, headers.

The factory header with the cat built in is that close to the engine for a reason. The factory needs the catalyst to get “lit off” as fast as possible to pass the government smog tests. The cats need heat to work, and sticking them in the pipe as close to the engine as possible let’s them pass the smog test, because that factory test has a cold start portion and the cats have to get hot as fast as possible to pass.

For us out in the real world, where we drive to a smog check station, having the cats eliminated from the headers and just mounted in the mid pipe downstream doesn’t hurt us, because the car is warm and the cats are hot by the time we get to a smog check station and they can scrub the exhaust clean.

It’s just science.

Thanks for the run down, already kinda had an idea on the long tubes after thinking over it. But learned something new on the cat placement and why.