Heads

I have a big block chevy I'm rebuilding. Can someone expalin to me open chamber and closed chamber? Wich is the best and why?

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The open chamber heads were circular in shape and closed were oval (bath tub shape). The open chamber ones breath better.
The better Big Block Heads are cast with "HD" on them near the casting numbers as I remember. These are the only good Big Block Heads . All the rest are junk or nothing to write home about. (I'm sure someone will respond and say they are running truck high deck heads and running in the 8.0's)
Since we live in the era of "the money has all gone to it's rightful owners" or "Barrett Jackson". The heads were expensive 15 years ago. Now in the new era they are almost priceless museum pieces.
You know after looking at this stuff for 25+ years. GM made the big and small block the same way. The basic and slightly high po engines (big and small) all had regular parts. Then there was the best, high performance engines that were like racing grade. These parts were not as plentiful as the regular parts.
Example the 1962 327/340hp had all the high performance parts and it had HP. Funny the 1968 -69 Camera Z-28 engine was almost the same engine. Funny how they both had a lot of balls and funny there both had almost the same parts (most expensive/highest HP). The LT-1 was very similar too. It all boiled down to that one HP intake, HP cam, Double hump heads, forged pistons, HD crank, solid lifters. A friend said to me 10 years ago and I doubted him, "it will cost you $4,000 to rebuild one of those engines)
My friends 68 Corvette 427/435 had all the engine castings cast with "HP"
Example, my friend had a 1967 Corvette conv't. Number didn't match 307 cid engine. He had a holley 4 barrel. 3:25 axle 4 speed. He couldn't light the tires up off the line in 1st. Then his neighbor gave him a 327/365 HP holley intake. (I thought a 327/365 was a Fuel injected engine). After installing the manifold he could light up the tires all day in 1st if he wanted. Look at what the manifold is worth if you can find one today.
The days of finding any of this stuff for $25 bucks (Bloomington in the 1970's ) is over. In it's day the HP Gm stuff was better than any edelbrock, mickey thompson, holley after market stuff.
Don't forget, this stuff was made back in the old days of GM, before GM decided to have it head up it's ass.
You don't get nothing for nothing anymore.
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Thanks for the information. Maybe I should better state my question. The long block I'm building now has flat top pistons. The original heads that came off the motor are (14092360...86-90...oval...OPEN...454 Truck, "peanut" round ports from http://www.mortec.com/bbc.htm ) stock. Correct me if I'm wrong, from what I understand the open style heads are suited to take a dome type piston to get a really high compression ratio. With My flat top pistons my compression ration would suffer because of the open chamber volume. I think for a flat top piston one would want a closed camber to help further raise the compression ratio to gain more power. Is this correct? Are there any known recommended Chevy castings that you know of? Are there any other things I need to know about?

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wrote:

If you arent concerned with originality, and you are going to use your car for street only use...seriously consider Edelbrocks Aluminum Oval Port Heads with their AirGap RPM Dual Plane Intake . I swapped out my 454 cid stock Heads and Intake with these...and I could actually feel at least a 30 percent greater airflow at the exhaust tips. The weight is considerably less versus the stock iron heads/ intake , and, based on this motor having the EDL Heads, Intake, bumpier Cam with Headers...their website dyno chart shows 540 h.p. Thats an increase of 150 h.p. over stock for an LS5 Motor. I then added an 800 cfm Mighty Demon Carb with annular boosters/mech secs....and the car is a real screamer with maximum low end to mid- range torque . Its darn scary sometimes when you jump on it. The EDL Heads are high quality CNC'd .
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snipped-for-privacy@gmail.com wrote:

Ya right, now pull my other leg!
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Careful.. Next Dave will be trying to pull on your middle leg if ya don't watch him!!!
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Sort of like the condom said to the teen age boy, "You're putting me on, right?" I don't think you could get much more than 21.6281% increase in flow with that modification. That's just a guess mind you, no hard facts or a web site to cite.
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I had a 69 427-435 (tri power manifold) a few years ago.
I was not going to replace that manifold (there is a small port tri power manifold also) so I was stuck with big port, open chamber heads. My pistons were not stock and were not flat. They had a very slight dome.
Are your sure your pistons are flat?
I think I would have done better with small port heads which would give you closed chamber heads. Like you said, only flat pistons here.
The increased torque of the small port, closed chamber head is the way you want to go with the low octane gas these days.
You cannot use the high compression setup and the open chamber heads do not get the compression ratio up without a large dome piston. With a large dome piston the CR would be too high. With a flat it is too low. That is why I push for the closed chamber head
Vito

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