Okay I looked up the casting number on my heads, 333882, and apparently they are crack prone and tend to run hot. Also, they have 160cc intake runners and 60cc exhaust runners. They are horrible flowing heads. Whats a good factory casting number head to look for at the junk yard? Whats a good intake/exhaust runner size to look for? Also, these are 76cc heads which I think gives me 8.5:1 compression. Would it be a good idea to bump it up to like 9:1 or 9.5:1 compression? Any info appreciated.

 

I was in the same boat a year ago. Everyone I talked to told me that for a 400 to run well it needed bigger intake then the old double hump heads. I looked for aftermarket heads about 190-215 cc runners. I setteled on Iron eagle 215's. My suggestion if you just can't find the money for aftermarket heads, Look for a set of 993's, They flow right with double humps but are a 76cc chamber. Or a set of early 70's vette heads. I haven't got the slightest Idea of a casting number though. But I bet someone around this place does.
John

 

Gotta say I agree with Spud. The big-ol' 400 just LOVES big intake flow. Getting the air into the cylinder is just as challenging as getting it back out. It's basically a big block displacement engine trying to flow through a small block cylinder head.

Do NOT be afraid of big intake runners with a 400. I put on a set of 200cc Dart Iron Eagles on my old 400 (cam just a notch hotter than stock- really mild) and lost NO bottom end torque while picking up MOUNTAINS of upper RPM horsepower. 4 full tenths and 4 MPH on a car already in the low 13s with no other changes.

There is no factory casting that will adequately feed even a mildly hotrodded 400. Go aftermarket. There are incredible flowing, cheap cast iron heads available from many companies. Just make sure that whatever heads you use they have the REQUIRED 6 steam holes, or you will have low speed cooling problems.

 

Well I do plan to mod this engine, and I have seen SBC aftermarket heads that have up to 230CC intake runners. Is there no decent set of stock heads that I could port to flow very good? Also, I have a 2 bolt, 2 freeze plug 400, which I am pretty sure is STANDARD BORE. I havent pulled the heads yet, but the oil pan is off and when I flipped the engine over on the stand, I noticed that it has GM pistons and a GM oil pump. As far as I know, engine rebuilders dont use GM pistons and a GM oil pump (they use melling i think). The year on the heads matches that of that of the block too, they are both august of 1980. how much would this engine be worth?

 

I know a lot of people dont advocate the Vortech head for the 400 but it isnt a bad piece for the money matched to a 400. The pathectic rod to stroke ratio of the 400 it uses the good quench factor well, and keep you out of detonation troubles. The steam holes will have to be drilled in whatever head you end up choosing and they will have to be ported to match the intake manifold to make th most of the cubes. And the cam will have to be matched as well.