Exhaust Noise Questions

[85lebaront2]

Vivek - The limited info I have is that detonation in the cylinder is reduced with a richer mix. That's because the more fuel in the mix cools things, and because the richer AFR tends to slow the ignition process.

Bill - Do you think if I were to change the AFR to 14.0:1 it might reduce the noise in the headers?

I'm guessing that the noise is the unburned fuel from one cylinder being lit off by the hot exhaust from another cylinder - in the header. Does that make sense?

14:1 would be leaner.

Gary, the last vehicle I had with headers was my 1966 Shelby GT350. After the original Tri-Y headers turned into Swiss cheese I replaced them with a set of Hooker large tube (1 5/8" primaries) specifed for Shelby and 351W Mustangs. The mufflers were Hooker header mufflers then two angled pipes that came out just ahead of the traction bar front pivots.

If you look closely, you can see the header muffler and the "tailpipe" which exited just ahead of the rear wheel.

That car was noisy enough that it was hard to tell what was making a specific sound.

[Gary Lewis]

14:1 would be leaner.

Gary, the last vehicle I had with headers was my 1966 Shelby GT350. After the original Tri-Y headers turned into Swiss cheese I replaced them with a set of Hooker large tube (1 5/8" primaries) specifed for Shelby and 351W Mustangs. The mufflers were Hooker header mufflers then two angled pipes that came out just ahead of the traction bar front pivots.

If you look closely, you can see the header muffler and the "tailpipe" which exited just ahead of the rear wheel.

That car was noisy enough that it was hard to tell what was making a specific sound.

I'm running 14.7 - 14.9 AFR at present, so 14.0:1 should be richer. Right? And I was just wondering if that might reduce the noise.

But I think all that might do is add fuel to the mix so there's more unburned fuel coming out. After all, right now I'm running right on stoich or slightly leaner and that should be the point where most of the fuel gets burned. Not all the fuel as the process isn't 100%, but if I add fuel by going richer then I'd expect there to be more fuel left over and, therefore, more noise.

And if this noise is due to unburned fuel getting ignited by the exhaust from another cylinder then that has to be somewhere after the exit of the headers as all the exhausts are separate until that point.

If it wasn't for all of the plugs looking so perfect I'd think that I have a cylinder misfiring and its unburned fuel causing this noise. And that's why I pulled the plugs. But looking at them I can't imagine that any one of the cylinders is misfiring.

And another thought - the ceramic coating on the headers could be contributing to this because it that keeps the temp up inside the header.

Anyway, I see the exhaust on your Mustang, Bill. Those were large primaries for that engine. Must have been winding it pretty high.

[ArdWrknTrk]

I'm running 14.7 - 14.9 AFR at present, so 14.0:1 should be richer. Right? And I was just wondering if that might reduce the noise.

But I think all that might do is add fuel to the mix so there's more unburned fuel coming out. After all, right now I'm running right on stoich or slightly leaner and that should be the point where most of the fuel gets burned. Not all the fuel as the process isn't 100%, but if I add fuel by going richer then I'd expect there to be more fuel left over and, therefore, more noise.

And if this noise is due to unburned fuel getting ignited by the exhaust from another cylinder then that has to be somewhere after the exit of the headers as all the exhausts are separate until that point.

If it wasn't for all of the plugs looking so perfect I'd think that I have a cylinder misfiring and its unburned fuel causing this noise. And that's why I pulled the plugs. But looking at them I can't imagine that any one of the cylinders is misfiring.

And another thought - the ceramic coating on the headers could be contributing to this because it that keeps the temp up inside the header.

Anyway, I see the exhaust on your Mustang, Bill. Those were large primaries for that engine. Must have been winding it pretty high.

The whole point of ceramic is to keep the heat inside, both to keep underhood temps lower and keep exhaust velocity (therefore scavenging) up.

Bill said he was winding the Shelby to 7k

Pretty good for a '60's pushrod V-8.