Washed Away. Mercruiser used rect port because it was the only head available besides the truck peanut port head. The large oval heads have not been made since the 70's.

Hello, 1Boatnut,
Most GM ovals will not run with the rectangular without work. Some will never measure up. We need to know the casting number or at least approximate year, which combustion chamber(open or closed), which piston you have.............
Without enought info, though, you are taking a chance trading heads. I would not do it until I had confirmation on what I'd be getting!!
Good luck no matter what. Post or pm and i/we will help all we can!!!
Oh yea, Formula31, I think, is correct about why they used what they did. They generally use whatever GM has that can be adapted:D

ok he said stock Gm oval to stock Rect. port, with a 509 and a good size cam, if you turn this motor to 5400 rpm's are more go with the rect. ports, but I am no expert,
Mark

Mark::) :)
Some stock ovals were pretty good, but I don't think they will do what he wants with that many cubes. The aftermarket or maybe a set of "049" casting number heads with mods will. Without the mods, I think I would go with the rectangles here. :D :D

blown1500,,,I think I have to agree with staying with my square ports..Like I said the only reason I was asking was because I can get the STOCK ovals for free from a buddy of mine and he swears by oval ports....
If I were to go ovals,I would probably go with aluminun heads..
Thank's for all your info. If I decide to go aftermarketI'll give you a shout.

Any idea when chevy switched to peanuts? I'm thinking that peanuts are oval port castings with a smaller plug in the intake port. I know peanuts are a zero on the performance scale, but why did the chevy gods changed to this casting? Seems that a standard oval would meet their needs in a truck head.

Just a curious mopar guy,
Washed Away

1Boatnut,
yes I am adding a supercharger.
I do however boat at 4000-6000 feet which adds a few more variables to head selection; blown or natural.
Dave

Washed Away!!
The "peanut port" head got it's name because the ports are about as big as a peanut. The smaller the port, the better they work untill you need more air than will go through them. If you want hp, that means more air. Chevy made these heads for trucks wilth a red line of about 4,200rpm. The main goal was very low rpm torque. Cleaned up, these are great in the proper application. They won't, however, feed most of what we use in a performance boat. I don't remember the year they went to the peanuts, but many of the guys here will know. It was in the 70's I think
Nordic Heat, the blower REALLY helps up there!!:)

I hope so :D :D :D

I think '84 was the last year large ovals were available as an OEM Chevy part. That left small ovals and rectangles as the only options until 96 (I think). Any one know if the '84 and older standard performance 454 from mercruiser made more than 330 hp at the crank with large ovals?