gt40 vs gt40p

[Unit 5302]

Originally Posted by goodyear1984

ur getting to scientific.6500 is fine for a 302.i mean up grading the cooling system come on dude i have a 347 with over 11.3 to 1 and mine is stock with electric fans doesnt go over 170.if ur engine isnt balanced good enough to 6500 u had a problem at day 1 when it was built u dont need to up grade bearing there only gonna go if theres a balance problem at this power level.if any thing get a good fluidine balancer or a pp balancer.there are so many people that do it to the stock bottom ends its not even funny.i ran 11.8 with a stock bottom end shifting at 6200 for 4 summers and 30,000 miles and now its in a carbed 85 still gettin the crap beat out of it. my friend has a 92 roller bottom end witha 150 shot shifts at 6500.its been done ive done it ive seen it..but that here nor there were talking about heads.bottom line if u can get a set of gt40 heads for a few hunderd and they dont need any work then get them any more than that get aluminum.its just stupid to put money in iron heads.they dissapate heat better via u can run more compression without detanation

Haha, my advice wasn't really for you. A 347 is going to run into issues with the GT-40 Iron or GT-40P heads pretty quickly once you start adding a couple other parts so for you, the GT-40Ps don't make any sense.

You can still find the GT-40P heads reconditioned with upgraded springs/valves on Ebay for $500 or so a set.

That said, there is no doubt aluminium heads conduct and dissipate heat better than iron heads so you're right about being able to go higher compression on aluminum heads without detonation. With good gaskets, there shouldn't be any issues with expansion rate differences between the cast iron (cast steel) block and the aluminum heads, either. I can definitely agree 100% with you there.