How many 9 second 396/375 alum head A/S A/SA

[Alan Roehrich]

Originally Posted by Cdncarnut

This is where things get a bit confusing for a newbie like me.

So, the NHRA allows someone to run an engine combination which was not available for that model year, yet I cannot run a cowl induction hood for the 350/255 combo because the engine option was cancelled before the cowl hood was released?

After checking the classification guide, I noticed that aluminum heads are also legal for the '69 iron block 427, even though that was never offered from the factory.

See my post above.

The GMPP 401 aluminum head is listed as an NHRA accepted replacement part for the early cast iron big block Chevy closed chamber rectangle port head. There is a HP penalty for using the aluminum replacement head. For example, we used them on a 69 Camaro 427/425, and that raised the HP rating from 425 to 435, so we had to add 80 pounds when running them in A/SA.

There are certain parts allowed by NHRA as replacements for old castings that are both difficult to find, and expensive to buy. In the case of cylinder heads, a HP penalty is applied, it usually starts at 10HP.

In the case of the 401 head, it is not allowing a different engine combination, it is allowing the 401 head to be used as a replacement for the OE head, with a HP penalty applied.

The same applies to some heads for other makes. An aluminum replacement head is allowed for certain combinations, and it carries a HP penalty.