Might be a stupid question? Copper exhausts?

Hi Guys,

Might be a stupid question, but IIRC weren't steel pipes used to absorb some of the lead from exhaust gases? Since (I guess) most of us are running lead free, is there still a reason why we can't go back to using copper pipes again? If I remember my motorcycling history correctly, weren't copper pipes used as they provided better thermal cooling + chroming wasn't so susceptible to bluing, etc?

What you all think?

H

Hegel said:

Might be a stupid question, but IIRC weren't steel pipes used to absorb some of the lead from exhaust gases?

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I've never heard of this theory and I strongly doubt it. The time exhaust gas spends in the tubes is close to nothing (it travels close to the speed of sound which is 450m/s in hot exhaust gas IIRC which means it takes a few ms for the gas to leave the exhaust. A smooth surface tube is not really a good absorber in the first place so the amount of lead which could be collected this way would be close to nothing as well.

Since (I guess) most of us are running lead free, is there still a reason why we can't go back to using copper pipes again? If I remember my motorcycling history correctly, weren't copper pipes used as they provided better thermal cooling + chroming wasn't so susceptible to bluing, etc?

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Well, I don't know when your mc history started but there's not a single copper tube in mine....that doesn't mean too much but I sincerely doubt that copper is a better material for exhaust pipes than steel for weight vs. fatigue. The best stuff at the moment is Nickel-base alloys like Inconel. In terms of exhaust pipes this is the material that is used for F1 exhausts. Titanium-based alloys are a cheaper alternative but Inconel can be polished to a very nice chrome-like surface finish. The only real problem is the price tag.


Tim

Exhaust gas waves or pressure pulses travel down an exhaust pipe near the speed of sound. The speed of the exhaust gas itself is much slower. Stainless steel is commonly used due to the fact that it is a poor conductor of heat. It keeps the exhaust gas hotter and keeps the velocity up which is a good thing for making power. Jim

Copper work hardens. Heat and fibration both contribute to the process, and fatigue cracking is the end result. Pretty hard to beat good old steel in that department. (Which is why it gets used for things like brake lines instead of copper)

Regardless of any other benefit I think you would have a hard time keeping them from coming apart at the head.

Nothing wrong with copper exhausts. It's been done and probably no worse for fatigue cracking than stainless.

My 1971 Renault 10 car had copper brake pipes and they were great, compared with the quick-rust steel pipes of other cars.

Years ago, when I was a noisy little sod, we used to replace our perforated baffles with any handy length of pipe. this was usually copper water pipe. It was always said that copper was illegal for use in exhaust systems as it released arsenic when in contact with exhaust gases.

I really have no idea if this is true :?:

comnoz said:

Exhaust gas waves or pressure pulses travel down an exhaust pipe near the speed of sound. The speed of the exhaust gas itself is much slower.

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Yes, you're right, I had in mind it was actually closer to the speed of sound but it's roughly 1/3 from what I've found in my old studies books. So instead of 3ms or something like this is 9ms or roughly 1/100 s. Still not a brilliant approach for an absorber which IMHO would rely on exposure time mainly and be "filled up" pretty soon due to lack of surface. I can't really imagine how this process of lead absorption would really work. AFAIR there's a few gramms of lead in a liter so an absorber "tube" would either build up a significant layer pretty quickly or catch only a negligible portion of lead.

I haven't heard this "steel filters lead" theory before and strongly doubt it so maybe somebody could elaborate a bit on this....


Tim

Triton Thrasher said:

Nothing wrong with copper exhausts. It's been done and probably no worse for fatigue cracking than stainless.

My 1971 Renault 10 car had copper brake pipes and they were great, compared with the quick-rust steel pipes of other cars.

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I'm not sure if I'd use a Renault as the benchmark for sound engineering practices. :wink:

The other issue with copper is that (depending on the alloy) can be soft, one ding (that wouldn't bother a steel pipe) and you've got unsightly pipes.

Not only that but cost has to be a consideration.