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Old 05-13-2005, 05:54 PM
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difference between closed & open chamber heads

what is the difference between closed and open chamber big block chevy heads? Why would anyone turn a closed chamber head into an open chamber? Is this a good idea or bad one, and does it change what intakes can be used. yes I'm just full of questions today.

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Old 05-13-2005, 06:08 PM
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just refers to the size of the chamber. Small, tight, heart shaped chambers are referred to as "closed" and larger, D shaped chambers as "open." Of course the closed chamber heads will be smaller, so you'll get more compression in the head, but generally open chambered heads flow a bit better, all else being equal. Most street motors have open chamber heads, as there is little need for more than 8:1 on a stock mill.

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Old 05-13-2005, 09:47 PM
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Closed chamber BBC heads are referred to as having "bathtub" heads because the chamber shape is like a bathtub... The open chamber BBC head has a more rounded somewhat heart shaped chamber that is more efficient both emissions wise and performace as well... You can use most closed chamber pistons with open chamber heads but of course you have to check to be sure... But in no way can you use an open chamber piston with a closed chamber head... (a grinder is not an option either)

On the intake question... You have 3 types of ports on BBC heads 1st the small peanut port heads used on trucks mainly (very good for torque but limited to below 5K rpm or less for HP and really more like below 4K)... 2nd is the larger oval port heads which are most likely the best for street and strip use and with larger valves and port & bowl work do good up to 6-7K rpm... 3rd... The rectangel port head is the all out performance head... While somewhat soggy on the bottom end for a street machine it lives for higher RPM`s and is really good when well prepared for the 3K-7K & up range (last BBC I ran crossed the line at a mere 7500rpm and was still pulling)... With all this in mind the block is what also determines the intake too... A tall deck block requires either special spacers to take up the space of a reg intake or you must have a tall deck type intake... I hope this answers some of your questions and right now I`m tired of typing and am hitting the sack... Just remember BBC`s or "Rats" do rule...
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