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Subject: open vs closed chamber heads

Original Message
Name: Chris Dagenais
Date: June 07, 1998 at 00:42:27
Homepage: My Car
Subject: open vs closed chamber heads
Hi, thanks for the info on oval and rect. port heads guys. I forgot to ask about open and closed chamber heads. Anyone care to explain that one to me. I know these questions are pretty basic but i'm only 18 and this place is gonna mold me into a chevelle guru! Thanks for all the excelent advice and opinions guys, all are welcome!
Chris D.

Response Number 1
Name: Dave Birdwell
Date: June 07, 1998 at 15:56:10
Subject: open vs closed chamber heads
Generally, closed chamber heads were used before 1971, and open chamber used from 71 and up. The main difference is in the shape of the chamber. It is hard to describe, you're best off to go to your local Chevy dealer and pick up a copy of the book "Chevrolet power catalog" There is a wealth of factory blueprint information for V-6, SB and BB chevys.
Most closed chamber heads have around 100 cc chamber, open chamber is around 118 cc.
The best example I can show is the LS6 crate motor has a 10.2:1 comp. ratio, because crate motors use open chamber heads. With the same piston, and closed chambers, the CR is 11.0:1. The experts say that open chambers with a domed piston will make more power than a closed chamber with a flat or small dome piston, the theory being the larger chamber unshrouds(more clearance between the valve and the wall of the chamber) the valves.(given the same comp. ratio and components)

Response Number 2
Name: Mark S.
Date: June 08, 1998 at 07:40:56
Subject: open vs closed chamber heads

Chris, I'd like to respond to this post and your previous one on rect./oval port heads. By the way, I've have over twenty years experience in building BBC's and testing them on dyno's, so this comes from personal experience, not from what I read in Hot Rod magazine.

I'll come to the point. If you want specifics, feel free to e-mail me. On a 396-427, use oval ports. If its a built 427(ie-L88), rect. ports are great. On 454's and up, use rect. port heads.

Air velocity through a 396 with oval ports is almost the same as the velocity of a 502 with rect. port heads. Thats because a 502 piston on the downstoke can pull more air than a 396 piston. Therefore you can run a bigger intake port on a 502 and not sacrifice ANY low end power. Of course this is all relative to what type of engine you are building and what the specs are of the engine. This is my experience with these great engines.

Again, I didn't want to take up much space so I didn't go into much detail. Daves response above says it all on open/closed chamber. Feel free to e-mail me for more info. Good luck!

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