Mustang3GT07

My buddie has had his steeda ones on for a year now and no problems.

Mach1man

For the amount of performance to be gained, it's not worth the risk. Because the crankshaft pulley is smaller, it causes an out of balance harmonic vibration,and it will fail eventually, especially if you wind the motor out close to the redline on a regular basis. The only true way to be safe is not to install the u/d pullies, or to have a new billett steel oil pump gear installed. And just an FYI, the Mach 1 came from the factory with an underdrive pulley alreadyinstalled for the alternator.