RE: [alfa] aluminum exhaust manifolds

["Peter Webb" <webb.p@xxxxxxxxxxx>]

> Aluminum has a melting point of about 1200 deg. F,
> which is also just about the same as the temperature
> of the exhaust gas under normal load.  I believe the
> exhaust gas temp can get as high as 1400 or 1500 deg.
> at WOT.
> Iron, on the other hand, has a melting point far above
> that (2800F, I believe??)

EGT's actually vary greatly by engine.   Dragsters run about 1600-1700 degF
EGT, some cars totally leaned out will reach 1500, but with modern EFI, they
run richer at high RPM to bring those temps way down.   The highest EGT's
are going to exist at low RPM and high load where the EFI is leaned out to
preserve mileage and emissions.

> If you devised a cooling method for the outside of the
> headers, then you could make it work, but then you'd
> be slowing down the exhaust gasses....

Enrichment is the way to cool EGT.   The cat needs some level of HCs to
cool.   A lean mixture and high EGT will increase NOX and melt the cat
anyway.

This is widely discussed in the DIY-EFI community where WB02 and ion sensing
systems use EGT as another input for mixture settings.

-Peter
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