mostdef

i have an 87 gt ttop all bolt ons tfs heads, headers, full exhaust, f cam vortech blower.. i have two crank pulleys given in my kit seems to be an 8inch and a bigger 10inch, which will make more boost??? i was running the smaller one but many ppl have told me to use the bigger one for more boost im just confused thanks..any thing will help

aode08

this is where you call and ask vortech.


You run too much, and you'll need head gaskets in short passion. Dont go past 10 psi

luckythirteen13

the bigger crank pulley will make more boost.

kweb288

you can go past 10, i know a guys pushing right about 15psi with stock head gaskets, and he's fine, and has been doing this for some time now

Timspony

as stated ^^^^ bigger crank, smaller blower pulley = More Boost!!

NoGo95GT

^^^^+1
As for blown head gaskets, it all depends on the tune and your fuel system. You can blow them at 4psi for that matter. I am pushing 15lbs of boost(18 degrees total timing) with the Vortech pulley and 8 inch crank pulley.

9550

reason why bigger makes more:


the crank pulley rotates once
the belt moves a distance equal to the circumference of the pulley. for a 10" diameter pulley, the circumference is about 31".
so the pulley rotates once, the belt moves 31". now, the supercharger pulley rotates 31". if the charger pulley is the same size as the crank pulley, it would rotate once as well, because they have the same circumference. but the charger pulley is much smaller. suppose it was half the size, 5". the circumference is approx 15". now, because the belt still moves 31", the charger pulley rotates twice.
the charger pulley is about 3", about 9" circumference. it will spin about 3 times each time the crank spins once.

so basically:
( the crank pulley size )/( the charger pulley size) x engine rpm = charger rpm.

so, the same way using a smaller charger pulley will increase charger rpm and thus boost, using a larger crank pulley will as well.

the supercharger should have a safe rpm range. vortech will void warranties (or so they say)if something goes wrong and find you changed pulleys.