metalergy

[victorfb]

i have seen a few differant header manufactures, and it seems they are all made from either mild steel or stainless. some coated, some chromed, some raw, and some aluminium coated. my question is. has anyone ever made them from all aluminium? logs yes, but never headers. why? why not? aluminium dissapates heat so well. wouldnt that be good? would they tend to crack easier?

[Rexone]

Aluminum (raw) melts at roughly 1200º+F. Exhaust temp is 1400-1600ºF. See the problem?
You can only get away with it with full water jackets and thick (cast) aluminum systems (they will fail immediately without water).
Some alloys of alum have a slightly higher melt point but it is still too low and strength at hi temps goes away too (soft) before melting.

[victorfb]

thanks mike. a very informative reply. i was and am still waiting for all the hacking from this one. but i just wanted to know. now i do. its great to know not everyone will slam you for a stupid question. but atleast i got a great answer. thanks man.

[058]

Many years ago [1962 I think] Pontiac had cast aluminum exhaust manifolds as an option for their factory drag race cars. Since these cars only ran a 1/4 mile at a time engineers thought the manifold wouldn't get hot enough to cause any problems, wrong! At the end of each 1/4 mile pass there were little blobs of molten aluminum puking out the end of the manifolds. It didn't take a rocket scientist to figure this wasn't such a good idea.

[Jetmugg]

058:
I was going to tell the same Pontiac story, but you beat me to it.
SteveM - Metallurgical Engineer

[victorfb]

looks like i may be able to get a job at the pontiac R&D center. :D