You do not need a new belt. The Steeda pulleys are engineered to be direct fit/use with factory diameter belts... As fas power difference, I don't know, I didn't install them alone. I added MAF/TA/Pulleys at the same time.
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// 1998 GT-Steeda Conversion \\ -- Sold
// Now own 2001 F-150 SuperCrew 5.4L \\
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