Crank is the IW OD pulley, which I measured as 7.9". Shift RPM is whatever, but with a 2.7" pulley it hits 18k at 6150rpm which is close to where I would like to shift. Whipple lists the continuous and max rpm as the same, which sounds conservative to me, im sure 18,500 (6300ish) wouldnt be a big deal.

 

So your 10% OD pulley is only a 3% really?

 

No, I measured the stook pulley to be 7.24 so 9.1% OD.

 

How did you measure it?

 

With a bigass set of calipers, and a second way by measuring the circumference with a string and dividing by pi. Pretty sure we had this conversion however many months ago when I did it

 

We did yea... i remembered you saying calipers but I couldnt remember where exactly you measured to. In the grooves or on top of the ribs.

A string will be in the groove as well. One of these days I am going to cut up an old belt to measure the circumference.

 

Best I can figure, pullies are measured at the bottom of the groove. Although on a pulley larger than a few inches it wont really matter. The groove depth I think is around 0.15".

 

Which when adding .30" it lands you squarely on the factory claimed diameter and the 8.25 it takes to be 10% OD... hmmm.

Sounds like they should be measured from the top of the groove. I guess that makes sense... you dont measure tire height from the depth of the tread.

 

I thought the same thing, but all my blower pullies seem to be measured from the bottom of the groove to match what is stamped on them.

 

Does it matter where you measure as long as you measure both the crank and blower pulley the same? It's just a ratio right?