I have a '76 455 that I am putting in my '85 ch*vy pickup. This originally started as a "don't touch the motor, just swap it in" kind of deal, which turned into a new gasket job, to a cam swap... now I just picked up a set of '72 heads to drop on it for more compression. Unfortunately, it looks like the '72 heads will do me little good right now, I checked how far the stock '76 pistons are sitting down in the hole, and they are .085" in the hole. Combining this with a .040" head gasket, this sounds like a recipe for detonation disaster. I would rather see the pistons .000" in the hole, then with the .040" gasket, would be right in the ballpark for the appropriate amount of quench. My concern is, can I take .085" off the deck without causing problems later? I would like to use the stock pistons over since they only have 68k originial miles, however if decking the block that much will cause problems later, I could consider going with a different piston with a higher compression height. Thanks!
Scott, just bolt on the earlier heads and go have some fun. You are not going to have detonation problesm with an 8.5 to 1 motor. Give me a call at the shop. Jim Burek
Detonation problems would occurr with higher compression, not lower. If you did take .085 off the block, you would definitely have to have the intake milled to properly line up as you will have changed the geometry of the intake to the heads/block. How many cc's are '72 heads? Are the pistons the stock dished ones? I have a calculator which can tell me what your compression ratio will be. Is the engine stock bore? Let us know. Phil
The pistons are stock dished. I did not check the CC's on the heads, but they are stock '72 heads so I'm figuring 71,72 cc's probably. My concern was, that going from stock 7.x:1 compression with the '76 heads, to approx 8.5:1 with the early heads, but having the pistons so far in the hole still that there is no quench, would possibly get me into detonation under heavy load/low-mid RPM usage, i.e. towing a heavy load up a long grade, etc. which would be a common scenario since this motor is going into my 3/4 ton pickup. If I bolt everything together as it is right now, the quench distance at TDC will be about .125" I'm just trying to cover all my bases while I've got the motor apart, I want this thing to be powerful, yet economical, and run good for years to come. I figure I might as well do it right while I've got it apart now.
Well, you're right on with the 8.5 to one with the 72 heads. Decking the block to .000 would get you very close to 9.97 to 1. My compression used to be right at 10.0 to 1. I used to have a pinging problem under heavy throttle unless my fuel was half 110 octane with Sunoco 94 Ultra. I am currently at 10.13 to 1 with my pistons .003 in the hole and no pinging problems at all running just 93 octane. This is becuase I then really polished up the combustion chambers and removed the casting button found in there. I used 70 or 80 grit flapper wheels for a dremmel tool that you can get at any Sears store. You'll need 4 of them to do both heads. You'll also want to get some grinding stones to do the bulk of the metal removal. When I was getting started I put the gasket on the heads, used a medium magic marker to trace the gasket and used the inside of the marker line as my edge to grind out to. This gives you a nice buffer so you don't go past the bore or gasket. This helps reduce the potential for that hot spot all around the circumfrance. It takes about an hour each combustion chamber and you'll need an old intake and exhaust valve to protect the seats, but it will be time well spent. Then you just get a 3-angle valve job done and you'd be all set to go. Decking the block isn't going to be bad, especially if you polish up the head chambers, just some $$$ because you will have to have the intake cut to make everything line up properly. Good luck. Phil
