Join Date: Aug 1998
Location: Waldorf Md. USA
The only way to verify the true performance is to put the heads on the motor and see if it runs better. Almost any head can be made to perform quite well if you do enough work to it. The flow bench and the dyno will tell the truth. If the ported 434's flow better than your 462's, all else being equal, the 434s should make more power. I am at home so I cannot look in my books, but the only other thing to watch is what the combustion chamber size is. If the 434's are much larger than your 462's then you will be dropping your compression ratio and power will also drop.
I don't have a clue what you paid for the heads, but in my opinion, and this goes completely against any business sense as I own a machine shop, anyone that spends any money to modify a stock GM head for performance use has not done his homework. There are so many aftermarket heads available for such low prices, that it makes no sense to use a GM head on anything but a stock vehicle, restoration, or a race class in which the rules say "stock GM heads only". This is the advice that I give my customers even though I can make a lot more money modifying thier heads than I can by selling them new ones.
Hope this helps,
Advanced Automotive Machine