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Old 06-10-2003, 07:29 PM
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Another Compression Ratio Mystery

To Anyone,

I have a aftermarket Chevy 350 engine installed in a 1990 C-1500 Truck that I have no idea what the static compression ratio is. Without tearing the engine to down to the heads, I would like to know the compression ratio by accessing the parts installed in the engine. I do have a few receipts for parts and labor that were from a former owner that I've listed below:

1). Center bolt Cylinder Heads- casting number 14102193 used on late model Chevy TBI engines. They have been machined (open bowled) for 2.02/1.60 valves and bowl blend(?). The combustion chamber is size is not known. The key here is to know the stock size of the combustion chamber (64cc, 76cc). No mention was made of machining or decking the heads.

2). TRW/Speed Pro flat top forged pistons were installed. Part number L2256F20 (.020 over).

3). Stock head gasket.

Well that's pretty much it. If anyone want's to use their expertise to access what they think the static compression ratio is.

Thanks,
Eric

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Old 06-10-2003, 10:51 PM
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Your chambers are 74 - 76cc, the term "bowl blended" refers to cleaning up the bowls under the valves, removing the ridge under the valve seat and just cleaning up leftover casting flash, this is good for street engines. with your pistons and overbore, your compression ratio is likely around 9.0 to 9.5:1 which is fine for a street engine on pump gas.
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Old 06-11-2003, 05:31 AM
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Double Vision,

Thanks for your reply.

I figured the compression ratio would have been at the lower range of 8.5 - 9.0 to 1. This brings me to ask anyone what gas octane rating should be used with this aftermarket engine? The spark plugs are picking up a deposit (dark crusty spot about 1/8" - 1/4 " diameter) on the intake valve side of the insulator tip. I've been running 91 unleaded premium with CR43TS plugs. Using colder plugs results in the same condition. The unleaded regular gas here in California is said to be "real hot", a real detonation problem in hot weather.

Thanks,
Eric
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