I've just run a couple of tests on my setup testing how restrictive the air intake system actually is on the 4jg2 engine. I have modified my airbox lid so it takes a KN 3" filter and made up a 3" pipe from the airbox to the turbo where it tappers down to 2.5". I haven't modified the inlet into the airbox at this stage just because I wanted to see how it would perform. After 200km of driving the restriction gauge has already recorded 25" H20 which is way to high. This is only on 11psi of boost. So if it's pulling this type of restriction with a modified setup what do they do in standard form with a stock filter and piping? I would hate to know. I will open up the airbox with a larger 3" pipe and run the test again to see what happens.
With this type of restriction its robbing hp and causing higher EGT's not only that but at 25" it will pull oil out of the turbo.
Will keep you posted when I modify the airbox.