ACE 350 Header Hiss

[Dzmitry]

Originally Posted by CSG Mike

That's.... sort of what I'm referring to but not really.

It's there to warm up the catalytic converter. If you don't have one in your header (which the A350 doesn't), it does nothing but make a lot of noise.

Gotcha, I did know that but forgot about it. I assume the effect of this to the secondary cat is lessened and not to worry about?

[CSG Mike]

Originally Posted by Dzmitry

Gotcha, I did know that but forgot about it. I assume the effect of this to the secondary cat is lessened and not to worry about?

correct.

[churchx]

Originally Posted by Dzmitry

I was under the impression that "removing the cold start" referred to simply lowering the RPM's the car revs up to on startup? Mine was shooting up from 2.5-3k on freezing days so I had my tuner take it down to about 2k. ..

Cold start is more then just higher initial rpms. It's also changed ignition and valve timings so to throw some unburnt fuel in exhaust to burn in exhaust.
For purpose, as others already wrote, to heat up cats sooner, as cats need to be heated up to working temps to do their job efficiently, and such design and tune specifics is what's needed for car to meet more modern emissions standarts that take measure emissions from cold start.
Those specific timings are much bigger contributor of extra loudness/noise of cold start then rpms alone, which probably you can easily check by yourself with comparing cold start noise level vs that of warmed up engine at same higher rpms. And tuning out cold-start in ecu tune means also adjusting those cold start timings, not just rpms.

[tomm.brz]

No change in valve timing actually, i know everybody read in steve' posts that there is overlap during cold start
there is no overlap, the cold start noise is just retarded ignition timing, a slightly higher set rpm and a slightly more open throttle body
EDIT: oh, and very very retarded Direct inection angle , that creates stratified combustion together with the earlier spray of the port injectors