Does anyone know if there are modifications needed to put 351 heads on a 302 block. I built up a new 302 and upgraded to 351 heads and then someone told me that the heads should have been drilled out somehow and that would make it a "Boss" 302 does anyone have tech info on that???
late model 351 heads flow the same as the 302 so if you are upgrading the heads the ones to get are the early style.... But the difference are the bolt size on a 351 windsors are 1/2" and they are 7/16 on 289/302...late model heads have 1.78 intake & 1.46 exhuast valves and early ones have 1.84 & 1.54 & also slightly larger intake and exhaust runners.
Ford began using the same basic head casting for both the 302 and 351W in 1977.
These later 351s, originally identified as 351Ks, have the rectangular 302 intake water passages and 6 intake manifold bolt holes. Original 351W heads have L-shaped water passages and 8 intake manifold bolt holes.
Also, the late model 302/351 heads have a larger water passage at the rear,
which means the intake gaskets are different between early and late models.
If you swap "real" '69-'76 351W heads onto a 302 you need to use the
351W style intake manifold gaskets, as the 302 gaskets will leak water
at the unique 351W intake manifold water ports.
You do sometimes need to drill out the steam pocket relief holes (there the real small holes you see on the head gasket) in either the block or head when swapping between 302 and 351 windsor parts. You use the head gasket as a guide. You just make sure each one in the head has a matching hole in the block.
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