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What is a good compression test number for a BJ8 ?

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bighealeysource

bighealeysource

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Hey all,
Tried to do a search on this simple subject but obviously not
doing it right so not finding what I am sure is out there.
What would be good to excellent figures for a compression
test on my 66 BJ8 ? I just did one and all cylinders are
over 150 but don't know how to compare that.
Thanks,
Mike
 
bighealeysource said:
Hey all,
Tried to do a search on this simple subject but obviously not
doing it right so not finding what I am sure is out there.
What would be good to excellent figures for a compression
test on my 66 BJ8 ? I just did one and all cylinders are
over 150 but don't know how to compare that.
Thanks,
Mike
Click to expand...
Many times I tested my cylinders and they were about 150ish and I considered that good. However, I had one cylinder a couple of years ago with 150ish and a broken top ring and part of top of the piston missing(unknown at the time). Another time a friends car had 175ish in one cylinder and the reason was excessive carbon buildup. If all the readings are close you are probably okay. Cheap compression gauge testers read different than quality ones.
Patrick
 
All with in 5 lb. Depends on the altitude. Up here at 6300 ft I get 130 and I'm happy. 150 is good at sea level. I think the cheap gauges are good enough if you are comparing from one to another.
TH
 
My BN4 has about 175 per cylinder. I have not tested the BJ8 yet.
I have a severly ported and decked head that raises the compression to 245. That requires racing fuel which is too expensive.

Jerry
BN4 with 3000 engine
BJ8 Just being tested with about 80 miles on it so far.
 
Hello,

I measured my 3000 Engine BT7 compression. Every cylinders with open throttle. Every cylinder press excactly 12bar (174psi) I think the important thing is not the absolutely high level result but nearly the same result at all cylinders .

Bye Michel-who don`t know the factory parameters
 
Re: What is a good compression test number for a B

I compression checked all cylinders on my 6-cylinder race motor when I changed out the break-in oil at about 300 miles. Each measured 185-190 lbs. I run 9.75:1 compression with J&E forged flat top pistons.

Dougie
 
Re: What is a good compression test number for a B

The best and most complete test is a leak down. You will need a dfferential compression tester, source of compressed air, and a method to position and hold the crank. Considerable work but you will know if and where leaks are.
 
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