Quote:
Originally Posted by bird72
So are 72 and 71 crossovers not interchangeable? Will repro work on 71? And another puzzle: some 197 heads are drilled for 2 end exhaust bolts and some only one? what I deduce from ebay ads. I just got set that have one hole drilled, and Ram Air Ent manifolds are cast for two bolts, so I should have shop drill end hole when do heads I assume (?).
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Anthony, which heads do you have? If you have 71 HO heads, you must use a 69-71 intake crossover. If you have 72 7F6 heads, you must use the 72 intake crossover, as it is different.
Are you going to use factory GM exhaust manifolds or reproductions? (or headers?) The factory exhaust manifolds on the 71-72 HO's only used 3 bolts to hold them on. That's why the 2 holes are not there in the heads. The reproduction manifolds use 5 bolts (copied from the 73-74 SD) for improved sealing. Therefore you will need to drill and tap the heads if you use the 5 bolt reproductions or headers.
The first picture is of the GM 3 bolts OE manifold. Picture #2 is a R.A.R.E. reproduction round port manifold. Pictures 3 and 4 are 72's. The last picture shows the different long slot for the crossover for 71. (the 71 197 HO heads will match this long slot)