I did a compression test yesterday and my number seemed low to me, i was hitting 300 psi in all cylinders. WEll yesterday being the hottest and most humid day of the year I decided to do a compression test. My numbers were 300 300 295 290. I redid the test today and it was 300 300 300 295.

I looked at the guage during each stroke and on the first stroke it went to 180 then gradually went up to 295. However it seemed to hit 250-260 psi rather quickly but took 3-4 more cranks to hit 295. This was the same for the rest of the cylinders, cranked to 250-260 quickly and then gradually hit 300. I know people say to add a teaspoon of oil into the cylinder to see it psi raises and i did that it shot past 300 easily. But if u put anything in the cylinder its going to raise psi, thats why i disregard that test. I have JUN III cams and probably need a valve adjustment

 

BTW This is on a b18c1 block with CTR pistons and b16 head, stock head gasket

 

I'm not sure what you are worried about, those #s are fine.

You are measuring peak pressures (transient) which from a measurment point of view is hard to get absolute consistency (without really fancy equipment). And this is a somewhat moot point anyways, as there will be minor fluctuations with how the rings/ valves are sealing. Also, you are likely within the margin of error on the pressure guage itself.

I'd be surprised if your pressure guage has an accuracy better than 0.5 - 1.0 % of Full scale. So for a guage with a full scale of 1000psi, the error could be as high as +/- 10 psi.

 

How many times are you cranking the engine?

 

10 times

 

Shouldnt you only crank it like 6-7?