Vortech Underdriven Crank Pulley Belt Size


Founding Member
Dec 9, 1999
Chilliwack, BC, Canada
I am currently running an old Vortech A-tim supercharger that is still on a 6 rib setup (6"crank pulley, 2.87 blower pulley).

I was looking to upgrade to 8 rib to minimize belt slip and came across an 8" crank pulley with a 3.6" blower pulley locally. This combo should spin my blower slightly faster (not too much, still within safe range) and I like the idea of the larger pulleys for more belt surface area and in theory less possibility of slip. I am already running a smaller 93 cobra water pump pulley and larger newer V6 power steering pulley so I am not worried about belt clearance, it should all work.

My question, the crank portion of my current crank pulley is 6" and even on the usual 6.87 pulleys the crank is usually 6" as well, the 8" I am looking at is an under driven 4.75" For those that have gone from a 6" to 4.75" crank pulleys, do you recall how much shorter of a belt you required?
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