[NOS2Go4Me]

Yup... it opens up a set of butterflies that flow air down the "secondaries" above a preset RPM. Depending on throttle and acceleration, they could open almost instantly or may take up to 5 seconds to open. It helps gas mileage around town HUGE, and on the highway too I suppose. Also, with the way the engine is tuned, it improves off the line torque by actually having them closed for some reason. Guys who have done the infamous IMRC mod that a guy called Waterboy on FF and FJ pioneered have reported gaining mid and upper rev-range power at the expense of low-rpm torque.

I'd rather get the larger throttle body and later on down the road the new cam and valvetrain assembly than do that mod. Also, apparently port-matching the intake manifold to the new TB helps out nicely as well.

You can actually feel it "hit" and the 1-2 upshift with the SPI lands the revs right at the actuating RPM, so it doesn't close. Same for 2-3. At least they got that right!