Looking for a little advice from someone who's done it. I'd like to bump the compression on my stock '60 235 from 7:1 to around 8.5:1 and was wondering if anyone has done this before. I want to stick to 87 or 89 octane gas, so I don't want to increase the compression above 8.5. How much should come off to get it close? I plan on an overbore, but I want to keep the engine looking stock, so no induction or exhaust change is planned. I'd like a little more torque for pulling onto the freeway; is milling the right way to go?
From what I understand, it was a fairly common thing to do in the wayback. Given the lack of higher compression pistons being available (i can't find any) I think milling might be your only choice for what you're wanting.
I cut the head on my 1954 model 235 .100 and cut the block .100. So far I have not had any sealing problems...but I had ARP make a set of studs to clamp the head down. I am running 13.5:1 compression pistons...and I figure with the block and head cut that I have raised it about one point. The pistons I used were made by Ross. Good luck with your build. Ron.
Yep, millin' is the way to go. Cut the block and the head. That way you gain on compression without makin' the head real thin and you have good surfaces. Only overbore it as much is needed to get straight bores. The displacement that you gain by boring is not worth havin' thin cylinder walls. Some of those blocks had bad core shift when cast. Meenin' one side of the bore was thick and the other was thin. Find a shop that can sonic check it for thickness. It mat be able to be offset bored to help the bad shift deal if it has that issue. Check your piston to intake valve clearance. The early Vette cam was a good piece also. Have fun,Smokey
If you mill the head on a 235 you must fly cut the top of the piston, as seen in the picture seen above. another option is to buy a set of pop-up ........ Which (watch for the blatant plug)........ I have and may consider selling. They're a N.O.S. set of 235" + 0.030 Jahns pistons. an esay D.I.Y. way of flycutting the pistons is to dry assemble the engine, plastiguage the inlet to piston clearance, then use an old valve coated with epoxy resin with fine sand mixed into it, reassemble the engine, and attach a drill to the valve, and use this to fly cut the valve to get 100 thou clearance.
Back in the dark ages of hopping up 235s, many rodders sunk the intake valves into the head the same amount that was milled from the surface. This required shimming the valve springs a like amount to keep seat pressure in line, and if the head was milled a lot (like .125), grinding that much from the valve tips and rehardening them. Rehardening isn't complicated--most guys would heat the valve tip cherry red and quench it quickly in oil. Because of the strange combustion chamber shape, milling any less than .060 won't make enough of a difference to be worth the bother.
Thanks everybody for all the great info! I knew if I asked the question on this board I'd get the answers I needed. Man, I love this place!!
rds... Talk about falling in love. I'm walking in the oil drenched quench as I dip my off set water jacket to the other side, (more in the middle). Man, I learned a lot.
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