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A friend of mine put together a sbc 327. He used a pair of cast iron heads from a 1990-91 sbc , I think vortec heads and used a 1970 sbc block. can this set up actually work together? The reason Im asking, well he got it running tonight and it ran like crap. Checked everything and it seemed to have vacuum leak somewhere. Vacuum gauge said 10 psi and I know thats not enough. Also you could hear a knocking noise coming from underneath the intake. What could cause that noise and also do you think these heads match up with that block? :confused:
 

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Well, it could be any number of things. First, Vortec heads are 96-98, definately not 91. However, the intake manifolds for all the 1987-1998 centerbolt valvecover heads have the 4 holes in the center drilled at a different angle then the old heads. Did he use an old intake and just auger out the holes? Did he make or obtain spacers to distribut the clamping load of the bolts? If not, there could be the source of a vaccuum leak. What rocker arms are on the engine? Center bolt heads use self guided rockers, they have big round pushrod holes that no longer guide the pushrods, so old stule rockers will not work on the newer heads without guide plates and screw in studs. If the rocker arms fall off the vlve stems, it's possible there are pushrods rattling around in the lifter valley . This would also cause very poor running, missing, etc.
 
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