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I've used them both ways and not seen much difference unless you have the
FI Head which has bigger ports. Even then the difference is pretty small.
(and you have to port the aluminum manifold to the ID of the ports to get
any real flow improvement. They tell me it is about 13%.)
There are 2 basic reasons to stick with the manifold you've got:
1. You've already got it. No searching, shipping, surprises when it shows
up (unknown condition, etc).
2. (depending on where you live) Winter driveability. The combined manifold
operates smoothly much quicker after startup than the aluminum one. Remember
that the vaporization of gasoline further cools the mixture, making it harder
to ignite. On the other hand, at high speeds, the mixture is in the manifold
for such a short time that it doesn't seem to affect performance much, if any
at all. Unless you are SURE the secondary butterflies are opening fully, you
should take them out (like the other guys said) and plug the holes. On my
first one I used sawed off 5/16" bolts (unthreaded shank) and stuck them in
with permatex. Worked fine.
--
George Downs Bartlesville, Heart of the USA!
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