1st Generation Specific (1979-1985) 1979-1985 Discussion including performance modifications and technical support sections

rebuilt engine comp numbers

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Old 05-30-09, 11:10 PM
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707

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rebuilt engine comp numbers

i did a comperssion test on my first rebuild (12a)
the numbers were 97-100-97
with only 200 miles on break-in with used housings and rotors. oem seals.
it was only cranking @ 120-130 Rpms. what do you think of these numbers? it was only on the rear housing as i did not have enough juice to test the front
how much does cranking effect the test as i know the rpm should be alot higher
Old 05-30-09, 11:58 PM
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Old Fart Young at Heart

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The FSM has a chart that relates cranking speed to compression numbers. Accurate results require 4 things, engine at operating temp, throttle wide open, altitude compensation and a cranking speed of 250 rpm. Since the chart only goes down to 200 rpm, I'd say your numbers are pretty good.
Old 05-31-09, 12:09 AM
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707

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trottle wide open huh? i guess it makes sense now i think about it
Old 05-31-09, 12:47 AM
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Yep, it does and many tester miss that seemingly minor step.
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