Monkey D. Luffy

I get the upper pulley is measured in millimeters and the lower is measured inn a percent i.e. 18% ... 18% of what?

The reason I am asking I had someone telling me that my pulley was too big & therefore making too much boost. I thought the lower the upper pulley size the more boost you make... could it be he was referring to the Lower pulley? And if so, which way should I go on the percentage... higher or lower? Just for an example, let's say I'm running a 90mm Upper & a 15% lower and want to lower the boost, would I go higher on the upper & leave the lower at 15% OR leave the upper at 90mm & change the lower pulley? I am very confused.

Any help would be appreciated.

black2010gs

Increasing the lower pulley size or decreasing the upper pulley size both spin the blower faster, generating more boost. So if you want less boost, either make the lower pulley smaller or the upper pulley bigger. I believe the % refers to the increase in RPM of the blower speed, so a 15% lower pulley would spin the blower 15% faster.

Monkey D. Luffy

Make sense, Thank You

ZMC2001

The lower bullies are also measured in inches. The 15% is s 9.25" if I remember correctly. Larger lower pullies also help to prevent belt slip as they create more belt wrap. Anything bigger than a 90mm is really big in my opinion for the upper, so you may be better off changing the lower. Also, if you have a too big upper pulley, you have to trim the vent on the hood to allow for adequate clearance. When Magnuson sent me the wrong pulley and I didn't bother to check it, it rubbed on this piece. I have since gone smaller on the upper and larger on the lower, but I wanted to make more boost, the opposite of you. Changing either pulley will work, but there are trade offs.

Monkey D. Luffy

Thank You