They are prone to cracking, especially at the Y where the #1 and #4 pipes
come together. The main reason to replace the manifold with a head though
is cost. A new manifold is over $400 and it's very difficult to repair a
cracked one.
The stock manifold flows well so there really isn't much of a performance
gain from a typical header although there may be some from a good one. The
headers cause the car to louder also. That heavy manifold seems to muffle a
fair amount of the exhaust noise all by itself. My car was noticeably
louder after putting on header - caused me to have to break down and by a
muffler too.
Brian '69 2000
Tampa, FL
http://web.tampabay.rr.com/oilleak/
-----Original Message-----
I think the common mod is to get rid of it and replace with a header.
Someone correct me if I'm wrong but I think the original exhaust
manifold is highly prone to cracking
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