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Old May 26th, 19, 05:56 PM   #1 (permalink)
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Compression readings?

Hi all, I just bought an all original 75 Camaro type LT with the original 350 engine with 185k miles. I took compression readings from each cylinder and I want to know if the readings are low and what do they mean...
Cylinder 1=110psi
2=120psi
3=110psi
4=120psi
5=110psi
6=120psi
7=110psi
8=120psi
What does this pattern mean?
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Old May 26th, 19, 07:58 PM   #2 (permalink)
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Re: Compression readings?

Tony, Those aren't bad numbers for a 185k miles. 10 between cylinders is fine. Did you warm up the motor, hold the throttle wide open, and turn it over at least 4 times per cylinder? Did you use a thread in tester or press in? I've always had better luck with threaded.
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Old May 27th, 19, 03:46 AM   #3 (permalink)
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Re: Compression readings?

I think back then that engine, new, was around 150 for compression
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Old May 27th, 19, 06:34 AM   #4 (permalink)
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Re: Compression readings?

I used a threaded tester but did not hold the throttle open...I forgot. I'm trying to determine if I need to rebuild the engine...
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Old May 27th, 19, 07:32 AM   #5 (permalink)
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Re: Compression readings?

That pattern to me indicates that the compressed thickness of the head gasket differed slightly between the two heads. The ten psi higher on one bank indicates it was compressed a bit more, or more likely the head has been cut down to obtain a flat surface to seal the cylinders in the past.

'75 is a smog motor with reduced static compression compared to a 1970 engine (last production year to have a 64 cc chamber). New heads not only offer better breathing through improved port design and larger valves but it allows you to pick your compression chamber volume to raise your static compression (which raises horsepower but also raises the octane requirement of your fuel).

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Old May 27th, 19, 09:05 AM   #6 (permalink)
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Re: Compression readings?

Thanks big Dave,
I too was thinking about replacing the heads with performance models.
Thanks guys!
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