Originally Posted by Matt Monson
I personally do NOT support turbo charging the NA Ej25 in stock form. Thicker headgaskets don't solve it because you mess up the timing when you do that. Being a flat 4 configuration you are retarding one side while advancing the other side an equal amount. Personally, I feel that the only correct way to turbocharge them is to add in an STi shortblock or to put STi pistons into the NA engine case.
Normally the goal of a turbo'd ej25NA would be to increase the horsepower with high amounts of boost. In that case the quoted part of your post makes sense. However what if he had an MBC set for a constant 2PSI? I would guess thats within the range to run 89 octane fuel with no intercooler and no pulled timing. Without an intercooler the additional weight would be minimal (essentially just the down pipe and turbo).
My suggestion for the turbo'd ej25NA was to maintain linear performance no matter the altitude. I have no experience with aircraft so I'm not sure if its an issue but at least this way the ECU would see a continuous airflow for the RPM during takeoff and cruise.