Exhaust Pops - Manifold?

[djones]

To cut a long story short...

When my car is really hot (ie doing a track day) it pops and cackles on over run:

http://www.themakoshark.com/gti/images/pop.mp3

I always thought this was unburnt fuel but somebody on another forum said it can be caused by the manifold. The manifold is an aftermarket 4-2-1 affair.

This sort of thing really interest me and I just cant get my head around why that could cause it. Any ideas?

The other thing I guess is its air leaking into the exhaust when it expands from the heat?

[RH1300S]

Mine pops and crackles when the idle mixture is very lean.

I'm running a pair of Weber 40DCOE's - if I run the car with one stage leaner idle jets it sounds like a full scale war going on behind me.

I assume that fuel injection settings must have the same effect.

P.S. - it sounds quite healthy to me.

P.P.S. - rolling road is the only real answer

[WhiteBlue]

All road legal exhausts do that if you run them really hot. The metal expands and contracts with the heating and cooling and there are internal baffles in most road going exhausts. All my multi cylinder motor bikes were making those sounds when I had done a nice hill climb up the Kessel mountain road.

[RH1300S]

All road legal exhausts do that if you run them really hot. The metal expands and contracts with the heating and cooling and there are internal baffles in most road going exhausts. All my multi cylinder motor bikes were making those sounds when I had done a nice hill climb up the Kessel mountain road.

While not wishing to disagree with you - I will add that the exhaust on my car is straight through. Although being a rear engine, the exhaust length is very short. In addition to pops and bangs I also get pyrotechics

I suspect that the cam design might have something to do with this too?

[machin]

With my hillclimb car I've experienced exhaust popping and banging due to two reasons:-

1, There was a hole in the exhaust manifold (out of view!) -letting in air and I guess mixing with unburnt fuel in the hot exhaust and therefore igniting. A new manifold without holes sorted it!
2, On the second occasion the fuel mixture was too lean -I guess (but stress, only guessing) that the fuel mixture wasn't very homogenous and therefore unburnt fuel was getting through to the hot exahust and igniting here. Either way, richening the mixture cured the popping and banging.

[djones]

In terms of cam timing it revs to 9k (peak is about 8200) so they are quite agressive cams. Well, its VTEC so that part of the cam is agressive.

For the mixture they are renowned for running a bit rich. I think part of this was for cooling at high revs.

[RH1300S]

I assume you have a CAT converter on your exhaust?

I wonder if these things run hotter than the type of systems machin & I probably have on our cars?

Maybe it's simply unburned fuel getting ignited while in the system?

[djones]

Yes it has a CAT.