Finding Engine Compression Ratio Using a Manometer on SBC ?

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Rt Jam

G-Body Guru
Mar 30, 2020
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Ontario Canada
I can't see how a manometer will tell you the mechanical compression ratio of an engine. Displacement maybe.
 
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Tynan918

Royal Smart Person
Aug 2, 2021
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Well I know for sure that the motor runs better on 91 and that was with 10% ethanol.. I know with the timing, really like anything in the 6 to 10° area... The throttle response from a dead stop acceleration sucks and it bogs real bad and sometimes it stalls and backfires out the carburetor.

If timing is set around 12 to 15°, the throttle response is a lot better and the acceleration from a dead stop is a lot better, but I have dieseling issues... And I think that's because of the 87 octane, I want to see if the 91 gets rid of the dieseling because fuel quality plays a factor in dieseling.
 

Tynan918

Royal Smart Person
Aug 2, 2021
1,136
249
63
Well I know for sure that the motor runs better on 91 and that was with 10% ethanol.. I know with the timing, really like anything in the 6 to 10° area... The throttle response from a dead stop acceleration sucks and it bogs real bad and sometimes it stalls and backfires out the carburetor.

If timing is set around 12 to 15°, the throttle response is a lot better and the acceleration from a dead stop is a lot better, but I have dieseling issues... And I think that's because of the 87 octane, I want to see if the 91 gets rid of the dieseling because fuel quality plays a factor in dieseling.
I actually found a Sinclair this morning that has non-ethanol 91 octane fuel...$4 a gallon 😎...
IMG_20220930_093730826_HDR.jpg
 

Supercharged111

Comic Book Super Hero
Oct 25, 2019
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Colorado Springs, CO
An easy thing to check is compression pressure. This will give you a big hint as to what you need to know.

It'll tell you cylinder pressure at like 200 RPM which doesn't tell the whole story. Is the cam known? I may have missed that.
 

Rt Jam

G-Body Guru
Mar 30, 2020
579
558
93
Ontario Canada
It'll tell you cylinder pressure at like 200 RPM which doesn't tell the whole story. Is the cam known? I may have missed that.
The whole story is unknown unless the engine comes apart and everything is measure.

Cranking pressure will tell alot about what fuel is required. The overlap of the cam will be exposed with this test.
 
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