moparchris said:
A leaky valve will gain nothing but a better idle quality. As far as the compression goes. It sounds like you have found a inept and not very consciences engine builder. Zero decking the block is different than just shaving the heads. The reason is quench. When you cut the head you will still have, we will use a generic number to keep it easy, .050 of clearance between the piston and the closed chamber portion of the head. When you cut the block .010 then you have a quench clearance number of .040. There is a sweet spot most engine builders shoot for, less than .050 to be exact. A steel rod motor can get as close as .020 without hitting at max RPM (rod stretch!) where as aluminum rod motors need closer to .050 to keep the piston from hitting the head. When you have the quench right the piston squeezes the air fuel mixture and sprays it into the chamber creating a nice flame front which is what you want for max power. Without this effect you are more prone to detonation. That is one of the reasons that the old stock 915 closed chamber heads make so much more power than the open chamber 906. An Eddy head is open chamber design. By my calculations from the info you have supplied I came in at 8.499. This is with a 10cc valve pockets which is what most custom pistons have for big block chrysler. If you cut the block .010 then it would result in 8.670. If you cut the block .010 and put a .015 head gasket in it (which is what a stock 383 came with) then you will yield 9.142. You would have to do all that and cut the head to 74cc will yield 10.077. Okay so you have to ask what does all this work mean to me? Well, from what I gather from reading the book Thermal Dynamics, moving from 9.00 to 10.00 will yield you 12% hp increase and moving from 8.00 to 9.00 will yield a 16% hp increase. Of course these are theoretical situations and the actual results will vary greatly. In your case this would be an increase of 40+ hp and probably a similar increase in tq. The heads would require a head cut in the .040 range. Yes you will have to cut the intake. I did this very exercise with my small block 360 after being frustrated with the performance. It had a static compression of 7.823 and I increased it to 11.14 and saw a 97 hp increase at the rear wheels. This was on a 350 hp motor to begin with. Some will say that its too much hassle. What has happened to me was I picked an intake to cut and stuck with it like your planning to do. If you need to change intakes then a good machinist will know what to do as long as you remember what you cut off your heads. Another thing to remember is that the heads have an open chamber design and the piston will have tons of clearance so dont worry about that. Most engine builders charge $500 to assemble an engine. I would want to see inside my $8000 motor that was built by a guy who didn't sweat any details. The cut on the heads will be $100 and the head gaskets will be a little more expensive, ($100 ) you will have to use a MLS (multi layer steel) gasket from cometic or fel pro. These gaskets will require a special finish on the heads and block but your already cutting both surfaces. So there you go. So you will have to spend another grand all said and done for 50 ish hp and a secure feeling that it will hang. Very worth it in my opinion.
Hey Chris, I am trying to find the .015 head gasket you mention, but having trouble. Where can I get one? Mopar Performance has a .020 gasket, but can't find .015. Also, regarding quench, am I going to be ok if he zero decks the block with a closed chamber aluminum head? He said he's going to "angle" mill the heads, he said you can get nice CR without having to cut the whole head. Thanks, John
