Posted by Dave Horvath [162.158.78.85] on Sunday, July 23, 2017 at 23:17:38 :
John S, son of John S, was looking for a head for his 251. He wanted the later style head with the extra water passage for the internal bypass water pump. I happened to have a spare 251 in the Power Wagon Emporium. The block had the hump head on it so I figured we were in luck.
Pulled the head and what do you know? It is a hump head without the extra water passage drilled! This was mounted on an early style block with no hump and the external bypass water pump. The block is bored .040 over, so I believe the head is a replacement.
Best I can figure, Chrysler had the new heads cast with the hump, but when used as a replacement head on an early block, they didn't need to drill the head for the extra water passage. That makes this a crossover head that could be used on either style of block. Didn't need the later style head gasket, either style would work.
Just goes to show, you learn something new everyday. We were thinking John could machine a hole in this head for his block and I can use a straight head on my block.
Anyone know when they switched to the internal bypass water pumps and what were the advantages? Any relation to pressurized system? By the way, all the "Spitfire" heads I have seen lack the hump, and no 251 heads I have seen have the asymmetrical combustion chambers like the high-compression 218 and 230 heads.
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