If you are questioning what year motor to start with for your big block Buick (BBB) build-up, this thread is for you. (If you are looking for a ’70 SF motor to build “because it has 370 HP,” you REALLY need to read this thread!)
I’ll cut to the chase and give you the answer right off. With one major exception, it really does not matter. The exception is the 75-76 heads. They are junk, due to their compression-killing open combustion chambers. Everything else is 95% comparable between every BBB ever made.
If you are concerned about factory horsepower levels, the fact is that the iron “hard parts” (block, crank, rods, heads, and manifolds—the stuff you might re-use in a rebuild) of a BBB have very, very little to do with the power output of the engine. Now, as Paul Harvey would say, here is the rest of the story…
Crank and rods
All BBB cranks and rods are identical, equal, and interchangeable.
1967 through early 71 blocks have a smaller oil pick-up passage. This is easily drilled out during machine work. 75-76 blocks are slightly heavier (about 10 lbs.) For anything under 500HP, this is just dead weight. And there is only a small horsepower window between where using a 75-76 block would be beneficial before you get to the point where you need a girdle no matter what.
If they pass a sonic check, 400-430 blocks CAN be bored out to 455, but you better send your machinist a Christmas card after that.
As stated, 75-6 heads are junk, due to the open combustion chambers. For the drop in compression between 70 and 71, most of the change was done through a deeper dished piston. The 71-74 heads have slightly larger combustion chambers, but not by much. They flow just a well as earlier heads. The emissions passages in 72-up heads do not affect flow. 67 and early-68 heads are known as “big port heads,” due to slightly larger intake passages. Untouched, they do flow a little better than later heads, but if you are doing any porting, it is just a “head start” for the porter. Any port job will go way beyond the flow of big port heads.
Stage 1 heads are just the same castings as regular heads of that year with larger valves installed. Any BBB head can become a “Stage 1 head.”
67-69 BBBs oiled the valve train through oil passages in the block and heads, into the rocker shafts. 70-up oiled through the pushrods. You can use through-the-pushrod oiling on any BBB, but, 455 blocks continued to have this oil passage in the driver’s side of the block. So, if using early (67-9) heads on a 70-up block you need to block this oil passage, either in the block deck, or in the head. The passage is in the front rocker shaft pedestal, right next to the rocker shaft bolt hole.
All intake manifolds will flow equally. As with the heads, any emissions passages added to later intakes do not affect flow. If you are putting a 67-71 intake on later heads, you need to block the AIR passages at each corner of each head, as the earlier intakes don’t cover them. There are also issues with the exhaust crossover changing in, I believe, 72. Some (all?) 67 intakes do not have the cast-in bosses to mount the throttle cable bracket.
67-69 heads use 3/8” intake bolts and 70-up use 7/16” bolts. Obviously, you use whatever bolts fit the heads. The bigger bolts go through the bolt holes in the earlier intakes just fine.
All exhaust manifolds flow equally. Some 67 manifolds do flow a little better, but not a big difference.
If I missed anything, or others have a different take on any of this, chime in!