Would anyone happen to know the diameter of the stock FD main pulley, or be willing to measure it? I'm talking about the portion of the pulley for the alternator belt specifically. I couldn't find the ratio in the technical data section of the '93 or '94 FSMs, nor through any searches of this section of the forum. The '86-'91 FSMs have the specs for FC alternators (1:2.08 ratio), but the FD FSMs seem to not have that info.

I will be adapting an FD alternator for use on my FC, and I'm looking to get the main to alternator pulley ratio the same as it is on a stock engine. I'm trying to avoid underdriving or overdriving it. I already have a stock FD alternator pulley, so I'm just missing the main pulley diameter, which will be necessary to calculate the ratio.

 

It was hard for me to be sure the caliper was centered in the pulley, but I measured 100 mm (or 3.9 inches) ID on the main pulley. Hope that helps.

 

Awesome. Thank you very much.

For reference, I measured the stock alternator pulley at 50 mm in diameter, so that makes the ratio 1:2.0. This is very close to the ratio found on an FC, and if you consider the error associated with centering the calipers, it may very well be the same 1:2.08 instead.