My simplistic understanding:

The airbox/port acts as a helmholtz resonator in order to improve engine air-flow at a certain rpm - guessing c. 2000-2500 rpm to extend the torque curve plateau lower for off-boost responsiveness.

Reservations with hypothesis: can't quite get the numbers to add up.

Assuming this is correct, thinking that switching to a second port (e.g 3x diameter) at certain rpm above the intened benefit area of the first one (e.g. rpm > 3500) could be used to push the torque curve up at the other end as well.

Insights from any engineering geeks out there?

Mark

You need to talk to Nigel <img src="/forum/images/graemlins/smile.gif" alt="" />

A few years ago Nigel built an airbox with adjustable vents in the side to try and create exactly what your talking about. Close the vents for good low rpm torque and then open them at high rpm to allow more airflow when the engine needs it most.
Unfortunately it made fccuk all difference but it did look very nice <img src="/forum/images/graemlins/smile.gif" alt="" />

I think the inlet is limited by its size and the amount of bends in it adding other inlet ports or drilling the airbox doesnt really make much difference.

Hehe - I vaguely remember Nigel's 'air-vent-on-a-wire' airbox. Cunning idea. Amazingly enough I seem to recall that he managed to actually sell it to somebody

What I'm thinking is that the actual port/funnel thing on the airbox makes a difference to its behaviour.. so you could modify this behaviour with another port (rather than only having extra holes) and switch between the two in a manner reminiscent of the VIS systems on n/a cars.

But I imagine you're right - probably just a convoluted way of making no difference whatsoever <img src="/forum/images/graemlins/frown.gif" alt="" />

I put a 4" tube on mine instead of the 2" OE one. Pretty sure I could feel a small pos. difference on the top! <img src="/forum/images/graemlins/smile.gif" alt="" />

Mazda used a system called VAD (Variable Air Duct) on the Mazda 6 in combination with variable length intakes and valve timing. The VAD system was basically an airbox with second port that opens at 4500rpm.

Using this you could actually make the main port smaller and longer knowing there would be no restriction when the second one opens?

The VIS system is pretty good. On my stilo it means it has peak torque for a large part of the rev range. The difference with a turbo car is once you are on decent boost it is probably beneficial to have no restriction at all so it is more on or off.

The frequency is *roughly* proportianal to sqrt(A/VL) where A is the cross-sectional area of the port, V is the volume of the airbox and L is the lengh of the port.

So putting a 4'' tube (of the same length) *ought* to make the intake more efficient in the region of 4-5k rpms.

The Mazda VAD system sounds exactly like what I was thinking of - if there's a commercial application then maybe it makes some difference <img src="/forum/images/graemlins/smile.gif" alt="" />

Making the main port smaller/longer would shift the factory tuned frequency up/down respectively... the advantage is that with two ports you can have two fillips on the intake efficiency at two different rpms.

Fair point John... maybe this idea is really only applicable to an engine when not running any forced induction (i.e. n/a or off boost) - though perhaps a switch between the airbox intake and a far less restrictive intake when the turbo is on boost would get the best of both worlds?

Well <img src="/forum/images/graemlins/smile.gif" alt="" /> You could install the ATPTurbo virtual exhaust system (VES) on your intake rather than the exhaust it was designed forsee here

When off boost you take the air from the airbox, but when on boost the actuator could open and you could take air from a induction cone as well. You would probably want it to work in reverse so that the airbox is on the 90 degree bend and the cone has the straight run.

Or else fit the actual VES bit so that it opens an extra hole on the airbox.

lol - I want me one of those!

By the by John.. do you know anyone who has one of those exhaust systems fitted.. perhaps as a cat bypass (that would be rather nice)?

Anyways... if I ever get round to it I'll try fiddling with a spare airbox and do a couple of runs... if I find anything interesting it'll get posted.