I’m a little confused about the evolution of the Buick 350 through its life. Will cylinder heads, intakes, cranks, etc., work on other 350s of another year? Is the main variance over the years the adding of emission controls and lower compression?
I will try to give a quick answer and I can add more info later: Blocks: 68-72 blocks work with only 68-72 heads as in 73 an extra coolant scallop was added to reduce head cracking. Using later heads on these blocks leads to coolant into the lifter valley as there is no block support under the head gasket at that port. 68-70 blocks have an oil feed up to the heads to feed the rockers. 71-80 blocks do not have this and the hollow pushrods feed the top end with oil. 73-80 blocks can use any year heads. Cranks: cranks are interchangeable except the 73-80 ones have heavier counterweights because the 73-80 rods are heavier. Rods: they can be swapped just rebalance the assembly if going from early to late rods or visa versa. Pistons can swap too, same deal. heads: all 68-80 heads are about 58 cc so no large gain to swap. Emissions stuff cam be plugged. 68-70 heads are more prone to cracking. 73 they fixed that issue with an extra coolant scallop. By 74 the design appears to have changed for the worse, head porters report these heads are harder to make perform. I think it was 75 or 76 when they added larger exhaust valves, but again that’s the lower performance head design. In my opinion the 73 scallop heads are the best as they are less prone to cracking but still have a good design vs the 74-80 heads. I plan to flow test a bunch of year heads to prove my theory. More info: The 68-72 blocks can ONLY use the NON scallop heads but this is where things get tricky! Some 73 heads have coolant scallops and some do not. 73 head casting numbers: 1242556 No scallops 1241861,scallops 1243452,scallops Has 74 on head You can plug the coolant holes in the head BUT if you try to run them without plugging properly then they will pour coolant into the crank case. The head gasket will cover the coolant holes but not stand up to the pressure, the block needs to have the scallop to support the gasket. 1241861,scallops 1243452,scallops Has 74 on head These 2 casting have the air pump holes that go from the intake to the exhaust ports. They mate up to the runners on the intake tubes used on the 73,74 and late 72 smog pump engines. If you use a different intake thes must be tapped and plugged. From ALL of the 350s I have torn down I have found lots of cracked 68-71 heads and NONE cracked 73-80 heads so this may be the reason why Buick added the extra cooling scallops and it seemed to work! The later heads do have a different port design slightly they are not all the same! Look for the later 75+ year heads with the 1.55 exhaust vs the normal 1.50. Steal The valves for your older heads. other random stuff... the later heads have steel rockers, these are less likely to fail but more likely to wear and get loose and sloppy. The early rockers are more likely to break but less likely to get sloppy. later blocks are taller deck heights so that further hurts compression ratios. at some point a larger oil pickup tube was added. ps I’m in Edmonton
