Cold Start Exhaust Note

[geoffdunk]

Hi All,

Does anyone know what extra mechanicals are at work to create the cold start exhaust "loudness"? I was wondering if this is achievable with a modification to be like this when wanted and not just when cold. I know the vacuum control opens and closes the rear silencer valves, I know that even in "dynamic" they are still shut off at certain rev ranges.

I have bypassed the vacuum control by blanking the pipe just to see what they are like always open and it doesn't really have a huge impact, a little loader but nothing really that exciting.

I now notice that on cold start-up which is always load on the RS4 and then dies down its even more of a raw sound and has that raspiness to it, is there any way of creating that sound or having that setting with a modification.

Does anyone know how that sound is achieved on cold start, and if it could be obtained through a modification and what would be the adverse effects, if any?

Cheers

[DeanoC]

Hey Geoff. It's caused by the secondary air injection system with the purpose of warming up the cats quicker. Basically it is pumping fresh air into the exhaust.

You couldn't run like that but i too am trying to replicate some of the rasp and volume.

For me none of the off the shelf stuff is hitting the mark. I plan to put an x pipe right up near the resonators and remove the centre muffler then re-programme the muffler flaps.

Kinda like this but with the x about 24" further upstream: https://youtu.be/PL77tK3Ilco

[DeanoC]

I'm still taking advice (particularly on whether to have the x on the straight or on the natural collision point from the collectors) but the rough idea is somewhere in the first circle and then take the opportunity to smooth out the bend in the second circle.

I will then code the muffler flaps depending on any drone in 7th and maintain full closure in comfort and non dynamic start up and idle.

[geoffdunk]

I am presuming there is no way to get that sound without making large irreversible modifications?

[DeanoC]

Nope. You are asking to make the exhaust note more raspy and louder. You will only get that by modifying the exhaust

[geoffdunk]

Cheers Dean, I sort of new that was the answer lol. Its a shame it can't be forced to make the cold start noise.

I'll be leaving it, I'm not one for modifying cars, when I trade it in the for the next I'll want it to be original s possible.

I should have leased it and hen I wouldn't care lol

[DeanoC]

Technicaly you could code it to work at all coolant temps but it would be crazy. I got a standard exhaust for 150 quid so ill be able to swap the middle around with the collectors and mufflers in place when needed

[MikeFish]

Isn't some of the noise also caused by the higher revs when in cold start? I thought the raspiness was caused by the cold metal of the exhaust.

[DeanoC]

Isn't some of the noise also caused by the higher revs when in cold start? I thought the raspiness was caused by the cold metal of the exhaust.

Both will have some impact but negligible compared to the detonations happening in the the exhaust caused by the oxygen being pumped in and meeting with the rich exhaust gas.

If you add 500rpm to the revs as soon as the air injection stops it makes pretty much naff all difference