Replacement heads on Stocker

[Alan Nyhus]

Originally Posted by SDT1DYI

It is curious how NHRA tech dept approves a replacement cylinder head when the runner volumes are considerable larger than their own stated specification. Steve Teeter. STK. 6380

A good example is the Edelbrock NHRA accepted head for small block Chevy Stockers.

- OEM head: 165 cc intake/65 cc exhaust
- NHRA specs on Edelbrock heads (5 hp penalty) : 172 cc intake/65 cc exhaust
- Edelbrock's specs on these heads: 185 cc intake/65 cc exhaust

When I asked an NHRA Technical official about this, I was told (paraphrasing) that if anyone showed up in Stock with the accepted Edelbrock heads, they would be illegal if they had the 185 cc intake ports. And if the intake ports measured 172 cc, they wouldn't pass because they would have to have been illegally modified (welding) to get down to 172 cc.