bryan1984

I am a newbie here so dont yell at me to much if this is a dead horse type question. so on to the questions........

We are going to rebuild our old 81 Chevy again. We hook to a sled with it so might not be the same as what a lot of you guys do. here are some of the rules we have to abide by.

473 ci limit
cast iron oem heads only
Oem blocks
114 octane is max fuel
1 carb, can be choke-less(dominators allowed)
no tunnel ram intakes, aluminum or cast iron
Roller cams are allowed
unlimited rpm


Here is the question. i have 2 sets of heads. A set of closed chamber rectangle ports and a set of open chamber large oval ports. (both are factory)We haven't bought our intake yet or decided what cam profile to run yet either. We would like to be in the RPM range around the 7,000 + for momentum and wheel speed when the pan drops. we are looking for about 12:1 comp also.

I am trying to decide which heads to use. We have run the rectangle ports before and made some good power with them. but i haven't run the ovals on anything before so didn't know which would work better. I was told the rectangles make better power in high rpm but the closed chambers are not as good as open chambers. I dont have the casting #s on me right now but i can post them later if need be. if ya need more info just ask.

STREETSLEEPER

iTrader: (6)

closed chamber, rectangular ports are the ticket. The same goes for old big block chevy heads. The closed chamber provides more compression and sometimes it gives huge compression hikes ( depending on the pistons ). Typically better flow is had with the rectangular ports. Anytime dealing with old chevy engines the closed chamber rectangular ports are the way to go. Those heads are typically found on the OEM High Output engines. Hope this helps.

bryan1984

that does help, that's what im looking for is everyone's input. i guess i should have stated that this is an old 454 block stock stroke and bored to 468 ci. I wish there was a engine dyno close and i had the time and i would swap the heads on the dyno and see which one made more power but i would need ovals and rectangle with the same chambers to really know which one makes power where.

STREETSLEEPER

iTrader: (6)

The oval ports with open chambers are typically used on the low compression passenger engines. While the closed chamber rec. ports were used on HO truck and HO cars. Take a graduated cylinder ( the kind we used in science class ) and flip the head over. See how much water each combustion chamber holds. This is how to determine the CC of the head. The lower the cc the higher the compression. This will allow you to calculate the compression ratio of each of the heads. You can also do this with the intake and the exhaust valve runners to see which one is larger. Remember you want more CC's in the runner and you want less CC's in the combustion chambers. This is what seperates the two heads apart.