Under drive pulleys

[MOP]

Last year I switched from a belt to a crank driven sea pump, it required the removal of my under drive crank pulley. It bugged me doing so, today I took it all back apart. Took the crank pump and my under drive pulley to my buddies machine shop, I needed to cut one land off and cut a seat into the other half for the pump base. The pulley is made of aluminum, sounds pretty easy! My bud has been shaving metal for many years the hardness of this grade blew his mind, we did not burn any of his fancy carbide cutters but this stuff was some slow cutting. Guessing it was it was some sort of coating as once through about .040 the going got easy, due to its design we had to cut through three varying surfaces but got it done. Tonight I plugged in the sizes to see the percentage gain. Best I can figure going to 5-7/16" from 6-9/16" Dia. is about 25% under drive, forgetting all the boasted HP gains from Hot Rod parts folks the link below says lot to me as it is not selling anything. I did lose a tad of top end after the switch, will dig up this post after testing to see how much I gain back for now it is my secret! But may surprise a few folks.

http://www.mpgenhance.com/pulleyhorsepower.htm

Phil

[DonziJon]

Could have been Hard Anodized. .040 deep sounds a bit unusual I would think. Hard to imagine ANY alumunum resisting Carbide cutters. John

[MOP]

Did not resist but came off in small chips instead of nice curley aluminum, you could immediately tell when you were through, was quite a bit slower cutting.

On a good note I managed to get it all back together just before it started to rain.

Phil