Later heads on an earlier block?

[Ponyak]

Has anyone put later pontiac heads (65 and newer) on the earlier blocks before 1964? I know that 70's heads will bolt on phisically but I'm wondering about the oiling passage in the early heads and not on the later. Also about valve clearance with the large valve heads used with the earlier small valve relief pistons? I know intakes are different. I have a 1961 389 short block with forged rods that I would like to do this swap to. Any info would be appreciated...Thanks

[MrPbody]

You pretty much answered a lot of your own questions. True, valve "angle" is different, '66-older versus '67-newer. If an aggressive camshaft with more than about .480" lift and/or 230 @ .050" int. duration, you MAY have an interference problem using the later heads on the earlier block.

Change the lifters, pushrods and rockers (all three is a "must") to '64-'66 units and block the oil passage coming up from the cam bearing (1/4-20 thread and a "set screw" will do it nicely).

The '61 block is "tuff stuff". A good heavy casting with lots of "meat" in the bores. The bell-housing pattern may make it difficult to use it in later cars. Starter bolts to the bellhousing, not the block.

Don't even THINK of using the '61 simply because of the rods. We call those "rubber rods". Even though they're a forging, they're made from a cheesy alloy (1140 if IIRC). They also have insufficient heat-treating and are subject to failure "without notice". The aftermarket replacement forgings (RPM and others) are far superior and quite reasonable in price (around $270 for a set).

What exactly are you "up to"?

Jim

[Ponyak]

This 61 389 is what is in my 66 Bonneville convertible. I developed an overheating problem which I found out is a cracked head. This block has been converted to the block mounted starter. I was hoping to keep the short block and update to the later heads, but after reading your reply I think I will look for a good later core to rebuild. Your expertise is greatly appreciated.