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Old 09-09-2004, 07:11 PM
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BBC combustion chamber sizes

what is the smallest currently available combustion chamber sizes in a Big block chevy design. Wondering if there is a closed chamber design available in both stock and or aftermarket aluminum heads. any idea how much compression could be gained over 781 heads?

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Old 09-10-2004, 10:00 AM
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As far as the size goes, you can send the heads to a machine shop and get them milled for fairly cheap. As far as the compression difference goes, you can assume roughly a 1/10th of a point of compression for each gained or lost cc in the combusion chamber. I am pretty sure that a 781 has a 118 or 119 chamber, so you can base your new compression off of that.

Adam
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Old 09-10-2004, 07:18 PM
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thanks for the response Adam.
I have already milled the heads .030" and decked the block .020". I am wondering if there is/was a closed chamber BBC head and how small the combustion chambers get. I think I have seen specs for a 98 cc head before, but I don't know if that is for sure. Especially wondering if some company has clued into the potential for a small chamber aluminum head for flat top BBC chevy's as a compression upgrade without having to get into the bottom end of the engine. How would the flame travel be in such a setup? Kinda like the small block combo of 64cc camels with flatops for factory 10.25:1 in a 70 350
Wouldn't a large oval port aluminum head with 85cc chambers (or something like that that would realize 9.5 to 10.25:1) be pretty cool?
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Old 09-10-2004, 07:26 PM
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the small...or closed chamber heads do give more compression obviosly....but they dont flow as well due to valve shrouding.
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Old 09-12-2004, 01:02 PM
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Okay,
I was just at a swap meet and saw semi open and closed chamber heads for 396-427 motors. both were large ovals. combustion chambers were tiny compared to 781 opens. will these heads make comparable power to the 781's? how is the port design? any input appreciated.
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