Hello to all, I new to this site, so bare w/me. I have a 1972 455 8.5 : 1 CR and a 1975 455 7.9 : 1 CR. The 1972 motor has "quench" type combustion chambered heads and pistons with deep recess, The 1975 motor has complete "open" combustion chambered heads and pistons with about half the depth recess of the 1972. My question is this: What will my combustion ratio be when I reassemble this engine using the less recessed heads and the quench chambered heads? I haven't the tools to cc and do the math but am thinking this is going to net me a 10.0 : 1 or better CR. Anyone have Charts or data on Dish and Combustion Chamber sizes they could share? Thanks for your help, Tom. BTW, I install these engines in Lesabres, 88s, and other 80s Full Sized cars. Its like a poor mans Grand Sport. 115.9 WB and 3500 lbs. coupled w/ 3.23:1 posi from 9c1 cars this makes for a hell of a sleeper and costs lest than $1,000 to get one on the road.
www.buick performance .com , go to buick tech, there is a piston, and a seperate head description thred
http://www.atlantabuick.com/CastingNumbers.htm combustion chamber volumes: 72 = 71cc 75 = 78cc i was under the impression that buick reduced compression from 70 to 76 through a combination of head volume and deeper dishes on the pistons (in fact, here's george's page on the subject of piston dishing - http://www.buickperformance.com/pistons.htm). if you've got shallower dishing in the 75 pistons you might have aftermarket or stage1 pistons.
I would have expected the same thing. The 75 motor was an uncracked motor, meaning all gaskets, bearings and internal parts were original. The pistons have a 3/16" dish depth with the perimeter undished area measuring 3/8" My 72 pistons have a 5/16" dish depth and the undished surface area measures 3/16". Seems I will gain quite a bit of compression out of these later pistons. I did have to revert to using the 72 block because of casting differences in the 2 motors. I was amazed that Buick would retool a motor for a 2 year run when they knew the 455 was going to be eliminated. Do you know anything about a universal head gasket that will allow the use of early model heads on 75 and 76 blocks? Thanks for your help, Tom.
its only wene you try to put 75-76 heads on a early block that you have to plug some holes on the 75-76 heads, or they will spill coolent into the vally pan area.
Thanks Kelly, Are you sure about the early heads going on the later block. I have both gaskets and when I lined them up it didn't appear there was enough material on the 72 head to compress the gasket and the top of the enlarged oval water passages. The 75 block is visually superior in quality and the increased water jacket size would be a definite plus. I would prefer to use it but am about tired of tearing down motors for a while.
