In my own experience, the only thing you can modify on the intake is the, Air Duck and the filter it self.

But if you really want to have more air input, why don't you open up the intake passage on the head, that is what we usually do, specially Mitsubishi family, I mean don't get me wring, it's Chrysler Damian design, Mitsubishi is the engine designer of the voyager engine...

Actually most of the people knows a lot about cars, they will tell you this process is called port and polish. But port and polish is basically finishing the metal on the intake port of the head. Originally the port on the head is what they called unfinished cut, because they leave it rough finish, so a lot of the Engine tweaker they port and polished the head so the air will flow smoothly into the chamber.
That is true, air is flowing smoothly and solid pack, to the chamber, I don't know if that what you really looking for, the way I understand your question is you want to have more air goes into the engine for a better compression ratio, if I understand you correctly, then you want to grind the head port, and open it a little bit, as much as possible you want to do this evenly around the port, and be very careful on doing so, do not make a big cut because you might get too deep and punch a hole on the water passage on the head, and before grinding the head port, cover the hole with rugs, and be very careful on the alloy chips you've cut, make sure none will go inside the head, otherwise you'll loose compression if one small piece of alloy get stuck on the valve and the valve sead.

The most safest way to do this is remove the head, but covering the hole with some cloth and a follow up of vacuum while grinding will do.

you can use any small rotary cutting tools, like Dremel.

Edited by DCM on December 25 2007 at 11:06 PM