2004 5.4 just wondering what a good compression reading would be ?
what is the high side and the low side?

 

I might be wrong on the actual numbers but less than 120 is low and high would be 180ish. anything in between is passing. Important thing is to look for consistency between the cylinders. they should be within 5-6psi of each other.

according to Alldata the lowest cylinder should be within 75% of the highest cylinder

 

Assuming the compression ratio is 9:1, then compression pressures would run ~135psi. Ford provides a span of ~106 to ~136. I'd suggest that 106 is pretty low possibly due to worn rings or a bad valve. If a cylinder does show low, run a tablespoon full of engine oil into the plug bore and try again. The pressure should go up considerably if rings are the cause of the low pressure.

Obviously, if the compression ratio is higher, the pressures will be greater. 10:1 should give ~150psi.