Compression readings

Hi all, I'm looking for some advice on compression readings. I have a 1.8 16v KR which is a non runner, has no ignition, fuel system ect. I've been messing around with a few bits but before I go too crazy I wanted to check the compression on the cylinders. I've read up on it and should expect around 150psi but I'm getting nothing like that, 75-90psi across all 4.
Does it make a difference that there is no fuel system (inlet manifold is open to the elements) and I'm cranking it with a battery and jump leads.
Thanks chaps.