maf and throttle body diameter

[The Radium King]

i'll have more soon. what i can say is that the oem rubber couplers are stretchy enough to fit the larger plenum, but you can also get silicone reducers to do the job (dimensions posted earlier in this thread). the aos line will fit, but perhaps get a hair dryer/heat gun on it to make sure it doesn't crack when repositioning.

the larger 3" inside diameter throttle body has a 3.25" outside diameter. further, the oem maf housing/airbox has a 3" inside diameter and a 3.25" outside diameter. so, you need a duct that is 3" inside diameter but will fit over something 3.25" in diameter. several options:

- you can get that spectre flex 3" duct with rubber boots on each end (the rubber should stretch to 3.25"). folks say to not use rubber, but it's good enough for porsche ...

- you can do similar to what pedro does and use the oem duct; cut the resonator box out and tie to a 3.25" long-leg elbow to the throttle body. that dog don't hunt for me, however, as the oem duct is very thin and will easily collapse if you tighten the hose clamp too aggressively.

- you can try what i'm attempting - throttle body to 3.25" elbow. saw oem maf housing off of airbox and attach to elbow (this gets the maf closer to the throttle body like on the 996/997 for more responsive readings). 3" flex duct to bmc dynamic air intake located where oem airbox once was. This is a bastardisation of what has already been done by insite and jhandy (and others i'm sure).

** edit to add that i've read in several places that using a bmw 3-series maf housing is equivalent to sawing off the oem maf housing however, having ordered one and compared the two, the bmw unit is 70 mm inside diameter and the porsche unit is 74 mm (so, i've got a bmw maf housing for sale if anybody wants one ...).