330 heads on a 307 Olds small block

[jae]

Actually Chris, you can run up to a '72 head (from #5, #6, #7 & #7a, with the 7a head the same as the 7 except for the hardened seats). Remember that Olds went to a dished piston in '71 but the 64cc chamber remained the same (I think the 330 heads had a 60cc chamber). I believe the chamber increased to 79 or so in '73, but the piston was not dished as much, if at all. I think the BB Olds had larger cc's to deal with the compression drop and most likely a dished piston as well - not 100% sure.

All Olds heads from the 1971 model year on used induction hardened valve seats to accommodate the federal mandate to operate on low-lead gas. No. 7 heads have hardened seats as well. The main difference between the No. 7 and 7A heads is the spring pockets. The No. 7 heads used valve rotators on the exhaust valves only so the exhaust valve spring pockets are cut deeper than the intakes. The 7A heads used rotators on both intake and exhaust, so the all the spring pockets are cut deep. And just to be clear, we're talking about the 7A heads, not the 7A heads. The chambers got big starting with the No. 8 heads in 1973.

With the exception of the 68-69 D heads, all BBO heads have the same 80-ish CC chambers. (D heads run 72 CCs). Note that 80 is the design volume. As-cast numbers tend to run a couple of CCs larger.

Yes, I would have put the 7-subscript "A" but was unable to get it work correctly - didn't want to confuse anyone with this and the later 7A so I used the lower-case "a". Thanks also for the clarity of the BBO info - I looked it up after the fact - was posting from memory.

But let's say the decision was made to put the 330 heads on the 307, wouldn't the head bolt holes need to be drilled larger (from 7/16 to 1/2)?

 

[KrisW]

There is that, along with slotting the pushrod holes on the early models. Drilling the head bolt holes is easy with the right tool. You just need the 1/2" bit that has the 7/16" dowel on the end for guiding the bit straight.

Most machine shops charge less than 50 bucks to do it, too. I had a machinist make me a bit back in the 90's but you can buy them now.

I did the same thing to my "C" big block heads as well for use on the late 70's 350. We also had to do it for a 403 project too.

This is all in a much older post from a couple of years ago and if I can find it I will post the link

 

[apj87442]

I removed the valves from one the 330 heads, labeled them, bored out the holes on the drill press after clamping it down on at work. I then reassembled the head. I have 8 exhuast valvles and 3 intake (trw pieces) once I get the other 5 intakes, the heads will go to the machine shop. I will be doing a compression check for a piece of mind before removing the 3A heads. I'll also be pulling the pan to ck bearings and to replace the oil pump for cheap insurance as well.