What is the "underspeed pulley" mod?

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Originally Posted by Flavor 987S

Is the Flat 6 part a Porsche part? Can any of you guys really "feel" at 5 HP gain? Is this a "while your in there mod" when doing the Serpt. Belt? Thanks.

No, it's a custom 4" pulley. I did the pulley as a reliability mod to prep my car for track use. My original P/S pump is still intact at 100k miles and 70+ track days... Yay! I cannot say I feel a difference but my car has some weight removed also. Others have ridden in my car and thought it was faster than their 2.5L but it's all subjective until you measure it.

If your car is mostly a street car and you love your stereo, don't bother with this.