basically anything that would prevent air from going from crank case to outside air would be the culprit.. Plugged PCV is not an issue, but maybe a problem with the airflow from your crank to your valve cover. Get a PCV in there and hook your lines to a catch can then back to your low side of the turbo to get the vacuum back.

 

Keep in mind things like carbon buildup would inflate compression numbers (like in Tanc's case I'm sure), hence why people now recommend leakdown tests, but not everyone has access to pressurized air and can do that test. Either way, you wouldn't get those readings even with carbon buildup if you have a dead ring.

Hence, your pressurizing the crankcase somehow. I would really start at the PCV and go over that stuff properly, hell, even set it up the way it was supposed to be stock to see if it helps (OEM Hyundai PCV fittings, run the lines to the IM) or both completely open with stock PCV fittings. Oil vapor can put a dent in octane, but at your psi level it shouldn't make much difference.

 

Is there anything besides the pcv and breather that would allow pressure to build up? Thats the reason I disconnected the pcv from the manifold, to eliminate a source.