QUOTE(Benny @ Apr 17 2008, 12:46 AM)

not for power, for mileage.

mileage? i've yet to hear claims on the tb spacer for that as well. with a throttle body injection motor, yeah, you're adding space to let the fuel atomize better, but with the MPI it really isnt doing anything. arguably, it increases the cubic inches on the intake manifold, but its barely measurable.
I'm adding a 63mm bored TB, new style intake manifold (longer, smoother, equal length runners), exhaust header, hi-flow cat and dynomax muffler (which i already have) with 2.5" pipe all the way to the muffler. that'll be as free-flowing as you can get, and as with any motor, making it breathe better not only adds power, but adds efficiency.
I also have a cowl intake setup which pulls air through the vent on the cowl through he firewall (which kills my mileage bc cold air = performance, warm air = mpg). with all this done I HOPE to be getting 20 mpg on the highway. I'm getting 17 now.
Keep in mind these things are as aerodynamic as a brick.