To break out the famed Air Dyno, we'd need quite a bit more information than you've given here: Which top-end package, compression ratio, camshaft specs, carburetor specs, exhaust system specs, ignition... Only then could we even remotely come close. Looks like you have a nice engine to start your performance build.
Old-School Meets New-School
Q I bought a set of Chevy aluminum heads for very cheap, but one of the problems that I have is that I cannot place their casting number anywhere. Some say they came from an '89 Corvette, and some say a '96 Malibu. The casting numbers are 10128374 and 10207643 (angle plug, no heat riser). I need to know their whole story before I can do anything with them. I am planning on putting them on a 355 with a high-lift cam-somewhere around a 0.560-inch lift. They will be going in a '89 Chevy S-10 with a 4.56:1 rear, headers, and slicks. The trans will stay with a TH350.
Are they the ones known as the Fast Burn heads? What are their limitations, in the lift part and spring size? What are the cc values for the intake, exhaust, and combustion chamber, in the factory form? What type of head bolts do they take (standard or long)? How about their rocker arm ratio? Head gasket thickness? Or type? As you can see, I am not familiar with aluminum heads; I'm more old-school, iron or nothing (but I'm learning). I need all the information you can provide me with to upgrade them for better performance in bracket racing. Thanks for all your help!
Raul Hernandez Jr.
A Let us start with our old standby: You need to go to mortec.com. This is by far the absolute best casting number identification Web site we've found, both in ease of use and accuracy. We almost didn't answer this question, but since you are an old-school iron head guy, you really need the straight scoop on these "cheap" aluminum heads.
The casting numbers you provided are heads from a '92-96 LT1 350 engine, very good production heads for a Gen II small-block. And that is the problem: They will only work on a '92-96 Gen II small-block! This is because of the reverse-flow cooling system that GM designed and first released on this engine. As the system is reverse-flow, it forces the cold water from the radiator into the cylinder heads first, then down around the cylinders and off to the radiator to start the whole thing over again. This was a great improvement over the Gen I ('55-91) small-block engines. It helped control detonation and gave a better ring seal by stabilizing cylinder wall distortion. As you noticed, the heads do not have an exhaust crossover, but they also don't have any coolant passages in the front or rear of the inlet manifold surfaces. It would be a little tough to get coolant through the inlet manifold. Also, the inlet manifold bolt holes are not in the standard Gen I location and are at a different angle.
For quick specs, the heads have 175cc inlet ports, 68cc exhaust, 53cc combustion chambers, 1.94/1.50-inch valves, and 1.320-diameter valvesprings. They accept standard-length head bolts and will accept either 1.5 or 1.6 rail-type rockers. To use non-rail-type rockers, you would need to replace the guideplates on the heads with hardened ones. The plates on these heads were only for assembly down the line. They have extra clearance and are not hardened.
Sorry for the bad news, but you needed to hear it. Hopefully, you will be able to sell them and get your money back. Or you could go new-school and get a '92-96 Gen II block for your buildup. They have some unique features and you can make good power with them. Good luck with your bracket-racing project.