With those pistons , I don't believe you can get the much by milling. Not only that, when the heads are sliced of very much, the intake manifold ports and bolt holes will not line up . There may be a referenced cut on the manifold to compensate, but Don't know for sure about that.
Which numbers are on your heads?? A 1975 would likely have heads with numbers ending in 493. Those are 120 cc chambers (big compared to the others at 76 cc.)
I would get just a normal clean-up cut on those. You could look around for a different set with the smaller cc chambers. Pistons are the way to get the compression your are looking for. Of course there are piston/head combos which can get you there.
The heads are disassembled so new valves & hardware would have to be installed but the heads are in really good condition. The engine was from a 1969 Deville- I have the transmission as well with a 12" tailstock, probably a useless unit
Yes it does.... the thought never crossed my mind until you mentioned it. Tell me, does the 1969 TH400 have converter lock-up? I doubt it... I'm a big believer in overdrive transmissions but if the converter locks up I'd still consider it. I had an old 85 Pontiac Parisienne (similar to the Bonneville) with a 403 V8 and a 200-4R, 2.93 posi diff, and I was getting above 20MPG if I went easy on the throttle. The .67 overdrive helped A LOT. The only thing is that the 200-4R is a bit weak compared to the TH 400. I lost 2nd gear after burning the rear tires off
Putting 76cc heads on a 75 block is going to give you between 11.5:1 and 12:1 compression. It would be easy to break something with compression that high and hard to find gas to run in it. I don’t think head milling can give much of a bump, but head milling and block decking might add up to ¼ or ½ a compression point. I have heard different numbers from different shops. However, check piston to valve clearances if using a high lift cam especially if you are using bigger ratio rocker arms. I plan to do a head shave and block deck to my 472 when it comes out of my 82 Eldo for a rebuild. I hope I get between 8.75:1 and 9:1 from it.
I had the heads trued up with a light cut, and the block also because of some small pits around the water passages. Not enough to raise compression much. It CC'd at 9.2 to 1 with KB hyper pistons. This is on a 500.
The early heads like the 76 CC types will accept larger over-sized valves than the later ones also. I have the 552 heads, with over-sized valves installed, but they are not as big as the early types. The info I have is that the later '74 to '79 heads can accept 2.10 intakes and 1.77 exhaust, while the early '69 to '73 will accept 2.18 int and 1.88 exhaust. Maybe not a big deal, but every little bit helps:thumbsup: