Rubik

So, I am sure all of you love the sound of the Macan at cold start. Nice, loud, and a lot of rumbling. However, after about 20 seconds or so, it dies down to a very well behaved sound. Still nice, but much more subtle.

I'm wondering what is the mechanism that changes the initial sound to a more subtle sound. Is there some kind of valve that opens at start up and closes up a few moments afterwards? And if so, why?

Also, is there a way to have that sound all the time without having to change the exhaust system? Would that be a small mod or big headache? Would it be reversible? Would that have any permanent impact on the engine due to flow pressure etc.?

Thanks for any technical input you may have.

NC TRACKRAT

http://www.macanforum.com/forum/engi...ap-update.html Here is a rather long thread on the subject from another forum. Consensus: The "Flapectomy" doesn't offer any additional benefit.

pman420

part of the problem is that when you cold start the engine it sits at a higher idle speed then settles down once it warms up a bit.

SteveFromMN

From what I understand the computer holds exhaust valve timing and inject fuel into exhaust to pre heat the catalytic converter. It doesn't last long on purpose so as to help reduce emissions and not increase them.

Rubik

Thanks for the input. Now, I'm going to pick your brain. You mean it happens at the engine and not at the muffler since the cat is upstream of the muffler and gas can only come from the cylinder? But isn't the opening and closing of the exhaust valves controlled mechanically by the camshaft? Must be a different valve?

SteveFromMN

I think what happens is the direct injection allows them to squirt extra fuel as the exhaust valve is opening therefore having extra hot exhaust heat the converter faster.
Everything is computer controlled. The injector timing and the valves also have a range of variability. Porsche calls the valve timing change Varro cam. Normally the cam timing is change at a high RPM but I think messing with this timing and injection timing can cause extra hot exhaust at low speeds to speed cat heating. As soon as the converter reaches temperature the process reverts to normal. It doesn't last very long.
This is explained much better on page 34 of Porsche Service Information 2009 Technik Introduction All 911 Carrera Models.
The section is titled Catalic-converter heating phase of DFI engines with dual injection.

Rubik

Awesome. Thanks! I'll read up on it.

1MORLAP

Flapectromy or unplugging the valve cable does provide with a similar sound. Saying that it makes no difference is wrong. Also consider lowering rear seatbacks.

NC TRACKRAT

IMHO, the "flapectomy" makes little or no difference. The aggressive sound at start-up doesn't change and it still dimishes after warm-up. FWIW, our F150 SuperCrew sounds much louder at start-up but much quieter after warm-up but our 993 C2S with Fister stage III mufflers will wake the dead at start-up and improves as it warms up. If you want the Macan to sound better all the time, the solution is sport mufflers.