[slowbird]

Originally Posted by PAUL K

Going from memory the car was running 11:50ish and it lost about a tenth with the aluminum heads. I think there was a slight mph gain with the aftermarket heads. It was a KRE aluminum d-port and a 250+cfm iron head

Its an excellent example of comparing "port volumes". The larger port volume heads made more power but couldn't run as quick.

Exactly why a well tuned 71 Trans Am will run away from a 336 geared LS-6 Chevelle.

Also a great example why "port volume" matters

A properly done set of kre d-ports with stomp iron heads imo. The kre heads Jim tested were out of the box from kre weren't they?