Re: 427-425hp w/GM 401 heads
 

All the info you are asking for is in the classification guide. I don't think there is any difference on the 396 aluminum heads (new or old) but i could be wrong, just be careful if you call it a 402 that changes alot of small stuff.

Re: 427-425hp w/GM 401 heads
 

We have a 427/425 with 401 heads. I would not build another one. If I get the chance, we'll be going to a set of 840 iron heads.

It is a good choice for a ZL-1, an L-88, or a Super Stock engine, and probably for a 396-375 or 402-375 in Stock.

Re: 427-425hp w/GM 401 heads
 

I come from the land of Mopar where things seem a bit easier. That being said, I have to ask a few questions: How did NHRA wind up allowing the "401" aluminum head as a replacement head for the 427/425 iron head combo when it has a 1.845 exhaust valve? Didn't this combo originally come in only one version and that being a 1.725" valve in an iron head? There is also the question about how did NHRA arrive at the smaller chamber volume with the 401 head?

I would gladly stand corrected if any of my information is wrong. Inquiring minds would like to know.