Underdrive Pulley

[Fudged Undies]

Brandon64, you will need to get a new, shorter belt. Smaller pulley would/should mean the belt will be too long and at least in theory should not affect the tensioner.

 

[TrainTrac]

As a previous owner of performance pulleys on various vehicles, here's a little question to consider. Does the tensioner allow enough flex to make up for the new extra slack on the belt due to the smaller diameter of the pulley?

I had underdrive pulleys on my '86 Mustang GT--Crank, H20 pump, and alternator. All I had to do was get a different belt. Once I did that, the tensioner kept it tight. I eventally had to remove the alternator UDP and put the stock pulley back on the alternator. With all three pulleys, the alternator wasn't running fast enough to keep my battery charged, and the car would die at intersections or at idle. I doubt you'd have that problem with just a crank UDP on the ST.

 

[Todd Z]

You need a shorter belt...

The mustang belt is 1.5 inches longer then the ST stock belt...

Once the pulley is on the st, just run a string around the pulleys in the correct path, and measure the length of the string, and get a belt 1 inch or so longer than the string..

Todd Z