For normal driving, especially in areas where it gets very cold, the one-piece
manifold is good. While I am pretty sure that you can get a LITTLE more power
out of the top end with an appropriately enhanced aluminum manifold, you can
get by VERY well with the cast arn manifold assuming your butterflies are either
working right or removed (and the holes sealed properly). And cold driveablilty
is MUCH better. Having said that, the heated area of that manifold is not
in the main fuel path and cast arn does not conduct heat very fast so if you
are doing sustained high-speed running, the intake part of the manifold will
be cooled by the evaporation of the gasoline (and the charge really doesn't
stay there long enough to get heated much anyway.) It is a GOOD, all-around
setup, as long as it is leak-free and crack free. The exhaust portion of the
manifold is just about as good as the early dual downpipe exhaust manifolds
and pretty close to the FI exhaust manifolds.

In an even trade I MIGHT take the aluminum manifold but for winter I'd have to
use a richer mixture. If it cost anything and the cast arn manifold were in
good shape, I would take it. I would probably remove and plug the holes for
the secondary butterflies though.

No, I would NOT get a header. I might get a bigger exhaust system though.

Note that there is NOT a comparable aluminum manifold available for the B30.
(Well, there arbuthnot commercially available anywhere I know of. The pres of
the German 164 club, Dominik Benz, has a triple sidedraft manifold on his early
164. I've been trying for years to get my hands on one! I think it is for
the AQ165 marine engine.)
--
George Downs Bartlesville, Heart of the USA!