Cold Start Exhaust Sound

[MikeM6]

I've noticed that my exhaust sounds deeper/louder at the end of the cold start cycle (after the revs drop to normal idle) for a short period of time, maybe 10-20 seconds. Then I hear a noise, possibly a valve or actuator, then the exhaust sounds quieter/normal. I originally thought this was the exhaust valves closing, but after watching the valves I confirmed they remained opened the entire time. Stock tune.

Has anyone else experienced this? Or is anyone able to explain what is happening during the cold start process that causes this difference in the exhaust sound?

Thanks.

[daytonaviolet]

i dont have an explanation of he cold start deeper/louder tones, but i removed my exhaust valve connections. this seems to keep the values open all the time giving it that deeper/louder tone all the time

[pennsiveguy]

Originally Posted by MikeM6

I've noticed that my exhaust sounds deeper/louder at the end of the cold start cycle (after the revs drop to normal idle) for a short period of time, maybe 10-20 seconds. Then I hear a noise, possibly a valve or actuator, then the exhaust sounds quieter/normal. I originally thought this was the exhaust valves closing, but after watching the valves I confirmed they remained opened the entire time. Stock tune.

Has anyone else experienced this? Or is anyone able to explain what is happening during the cold start process that causes this difference in the exhaust sound?

Thanks.

I know exactly the sound you're talking about. Apparently after the cat warmup higher-RPM period, there's another period of about 10-20 seconds where the A/F ratio and/or the ignition or valve timing is different, and it gives the exhaust a deeper sound. Perhaps someone more knowledgeable in the startup engine management algorithm could tell you more precisely what's going on during that period, but something is definitely different. Doesn't do it on a warm start ever.

[VETTEPRO]

The computer retards the timing in order to heat up the cats. Retarded timing equals higher exhaust temperatures.
When running modified exhaust and downpipes, it is annoyingly loud. It can be tuned out.
My Z06, with headers etc. would wake the dead on a cold start.

[MikeM6]

Originally Posted by VETTEPRO

The computer retards the timing in order to heat up the cats. Retarded timing equals higher exhaust temperatures.
When running modified exhaust and downpipes, it is annoyingly loud. It can be tuned out.
My Z06, with headers etc. would wake the dead on a cold start.

Thanks for the explanation VETTEPRO. IMO the exhaust sounds better when the timing is retarded, at least at idle. I guess I need a louder exhaust.

[VETTEPRO]

I play with exhaust quite a bit. My favorite, so far has been downpipes and stock mufflers with an X Pipe. The X Pipe changed it dramatically.

[MikeM6]

Originally Posted by VETTEPRO

I play with exhaust quite a bit. My favorite, so far has been downpipes and stock mufflers with an X Pipe. The X Pipe changed it dramatically.

Interested in more details. How did the X Pipe change the sound?

Which downpipes and x-pipe are you using?

How is the gas smell with the downpipes?

Thanks.

[NikNala]

Originally Posted by MikeM6

Interested in more details. How did the X Pipe change the sound?

Which downpipes and x-pipe are you using?

How is the gas smell with the downpipes?

Thanks.

I’d also like to know if the x pipe took out the raspiness. The stock exhaust with catless downpipes has too much rasp for me.

[VETTEPRO]

Originally Posted by MikeM6

Interested in more details. How did the X Pipe change the sound?

Which downpipes and x-pipe are you using?

How is the gas smell with the downpipes?

Thanks.

The DPs are Racing Dynamics. I think downpipes are downpipes, for the most part. There are some that are 3 1/4" that would make a difference on a car with larger turbos. I just took the stock X Pipe from my C7 Z06 and welded it in place. It fit perfectly.
It's not bad but I feel a little guilty. I'm going to weld in a set of ceramic matrix cats and see how that works.

Originally Posted by NikNala

I’d also like to know if the x pipe took out the raspiness. The stock exhaust with catless downpipes has too much rasp for me.

It's hard to quantify or describe the sound. It got rid of a lot of raspiness and smoothed it out. It made it quieter that I thought it would. I think it's just about right. I thought it was too loud without the X Pipe.

[Fishreeler]

Guys, got the perfect exhaust sound.

I didn’t want to install sports catalysts initially, since in any case they reduce the exhaust gas throughput and also tend to be destroyed, although they are much more durable stock catalysts.

Installed downpipes and trompe lambda probes, so as not to open the computer, while maintaining a guarantee on the engine and transmission.
The exhaust sound turned out to be almost comfortable in volume and an unpleasant 'grunt' appeared))

I was advised to install two resonators immediately after the standard resonators. Resonators ordered. Material - stainless steel, quality of work - high. The resonator has an inner diameter similar to the diameter of the exhaust pipe.

Installed resonators, received a noble and wonderful M-th exhaust sound. Happy as an elephant and as happy as possible))