[Darren]

I dont want to open a whole can of worms but basically induction kits/filters are an aftermarket item that is not of much value per ££ spent on most cars, more so subaru because they actually do a good job on R&R from the factory!

Its not all about the amount of air you can force into an engine when you are looing at anything producing over 150 BHP air temp is a major factor, hense why virtually every Turbo vehicle runs and intercooler, the cooler the air the denser is it there forfore more O2, my Impreza runs a spray onto the intercooler to keep temp down and my Evo had water injection to do both.

All the (mushroom) filters are doing is taking large particles from the air that is HOT from the engine bay, the factory air box will be fed from outside of the engine bay and as it act like a storage unit will actually cool the air by 1 to 2 degrees.

The only way and after market set up will work is if as mentioned if it can produce either a ram air effect ( forced induction from air speed) or by supplying the engine with cool air, IE from out side of the HOT engine bay.

Have a look at the induction on any evo or high performance motorsport homologated road car and you will see an inlet system from outside of the engine bay and not the inner wheel arch in most cases.