Hi everyoneI am restoring a 77 Trans Am and I put the 400 block and heads in the machine shop. Couple of weeks went by and they told me the block needed boring and one of that 6x heads was cracked. I found a set of 093 heads on Craigslist and of course the guy swears they would make the 400 go faster.. I haven't bought them yet just wanted to see what you guys think. Thanks
Wallace racing lists those heads as 1966 389 or 421. Have to be closed chamber and resultant CR is 10.5-10.75:1 which is bad news for Pontiac iron heads on todays pump gas, They both have small valves. If I rmember correctly, Pontiac changed their valve angle in 67 so the reliefs in your pistons may not match the angle of the valves in the heads.Also, after 75, Pontiac blocks had less castiron "meat" in thier castings since the smog motors of the late 70's were low compression so I wouldn't want high compression heads on a post 75 block.I'd steer clear of them.
Thanks for the info.. So should I just attempt to put other 6x heads back on the motor? I want around 300 hp.
Yes, I'd stay with a 6x head for your application. 300 HP is not hard to make.
can they repair the cracked head?will they warranty it?is your eng stock or have a cam?either way you can boost torque and hp slightly by having them milled .025" from stock to boost compression.if you have a cam you can install larger intake valves or get them pocket ported or simply back cut intake valves.