Here's how I would figure it:

Compression = (Compression Ratio minus one) to the 1.2 power multiplied by Atmospheric Pressure. Atmosheric pressure at sea level is 14.7

So, in your case:
13.5-1= 12.5
12.5 to the 1.2 power= 20.71
Sea Level is 14.7, so let's use 14.0 for Ohio
20.71 x 14.0= 290PSI

Seeing 290psi would confirm your compression ratio at 13.5. Don't forget that base gasket thickness, piston protrusion, chamber volume, etc. all effect compression. But this formula will get you in the ballpark. What is more important is that psi value is consistent across all four cylinders.

 

I usually get around 240 when I check the cranking pressure, that is with the Muzzy 1270 kit... this might be a duh... but make sure you pull all of the plugs and and open the throttle when you are cranking... oh and a fully charged battery could make a diff...

 

ive got 200 to 210 on several stockers ...and 150 on 9.5 to 1 turbo pistons with ape springs and thick head gasket ....

 

cranking compression is directly affected by cam timing...if you are seeing 220+ on all 4, I would say yu are good to go without know all the variables!

 

I've found that I have a weak cylinder. It was 150-160. The rest were over 200. So far, I think it may have been the way the cylinders were prepared. When putting a set of drop in pistons in, should the cylinders be honed? They were lightly honed with a 320 grit flexhone. You can still see the crosshatch and I've been running the **** out of it all year.

 

What psi should I have on a compression test .200-230

 

do a leak down test that will tell you were youre losing air pressure at by the valves most likely may have a tight shim leakdown will even help you find witch valve is leaking if one is.

 

mine pumped put 220 per cylnder

 

check your valves, this will cause the compression to be lowere in that cylnder. I have two valves out of svc (one in each cyl)

 

put a busa in it Mark that will fix it! :kidding:

 

cam timing will affect cyl pressure . ive seen as low as 130's on turbo motors and as high as 280's on high comp. motors . I look more for cyl-to-cyl differences when looking for a possible hurt motor .