is there a way to calculate what size belt you will need when switching to an underdrive pulley set? if not, does anyone know off the top of their head what size belt is needed for a 91 L03 with A/C and smog with a March power and amp series underdrive kit ?

 

you could try googling it or searching on ebay, sometimes sellers give that info. you could try some string around the pulleys see how long it comes out too. I had the basic black set with crank and alt. pulleys the belt was 923k6, thats 92.3" stock is 94.5". It doesnt tell you in the instructions? or at their website?

 

+1 i've used the string before and it works great I also have a set of underdrive pulleys coming in and will do the same thing to meassure