did this to fit the 3.4L. this is a BMC DIA air box with a MAF housing out of a BMW 540i and some custom silicone plumbing. sounds awesome.
the DIA box is around $200. the maf housing was $20 from someone on bimmerforums.com. the silicone hoses, joiners and clamps were another $200, but that's only because i had to buy a 135deg hose from samco to fit the angle of the 3.4L. that one was like $100.
if i had to do this to a regulat boxster, it would be around $265 total.
FYI, in this process, i found out that a lot of the aftermarket intake kits use the STOCK tubing & just swap out the airbox for a 'cold air' box. the BMC DIA is closed & you can plumb the airbox inlet directly to the car's body inlet.
props to cloudsurfer w/ the design idea & to JAAY for a lead on the MAF housing.
