I am building a .030 over 454
Gm 3964290 heads 101 c chamber
Intake is a gm 3854100
9to1 compression
800 Holley


Would I make more power with rectangle port heads and intake?
looking for a good cam? Was considering something along the lines of a crane 139731 las112

I have 290 cc Edelbrocks on a 454 .030 with 1/4 cranks ( 489 cubic inches ) 731 cranes installed @ 107 . 9 to 1 compression. They made 616 hp and 606 hp with custom Tim Zepp built and tuned carbs.

Added some 250 blowers and chillers to same engines 2 seasons ago ... port matched oval heads to regtangle port intake and made 785 hp ... same tuner with larger custom carb.

The non blown dyno pull is on YouTube ... type 489 on the dyno and scroll down to the 489 marine engine with blue merc valve covers .

Wow that's some good numbers! What headers was run on the dyno?
But I was asking about gm 3964290 heads? Has any one run them on a marine 454 if so how did they do ?

What size valves are you gonna go with? I ran some 206's and left the stock size valves in them and the motors ran out of air at 4200 rpm.So by the time you make the valves large enough and put good seats in them, you could by a good set of aftermarket heads.

They have .219/188 valves. Heads are freshly rebuilt with about 40hours on them. Are these to small to?

I think you will be good with those valve sizes. You need a better intake and port match those heads with some good gaskets. If you may be looking, I'm getting ready to list some parts for sale and I have some polished rpm airgap intakes that are port matched already and you would have to just match the heads.

I did the same a few years but but used a Mandra Custom roller and Dean Gellingner port matched the RPM Intake.

Ran like a dream.

Remember exhaust is everything, and was not mentioned in posts above.

Keith Eickert cast headers with dry tails in boat ... dyno pulls with automotive headers