The pulleys are smaller. They are for your alternator, Crank shaft, and fan. They make the belt go slower. So it frees up the power that would be used to turn the belts. If you have a big sub in the car dont get them. I had one for a while and the car would stall. So I did what any real Mustang fan would of done,
get rid of the SUB. Other than that if your car has lights that make it look like a X-mas tree. Go and get them.
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1988 LX 5.0
Drivetrain: 2.73 Stock Gears, World Class T-5, Lakewood Bellhousing, Summit Adjustable Cluch Quadrant & Cable, Alumminum Driveshaft, Flaming River Manual Steering Rack
Suspension: MAC Control Arms,Maximum Motorsports Front Grip Package, H&R Sport Spings, Bilstein Shocks
Engine: Steal Mounts, Ram air, K&N, Under Drive Pulles
Exhaust: 1 5/8 Un-Equal Length Mac Headers, X-pipe W\cats, Edelbrock cat\back