shnook357

hey guys wats the difference between the underdrive and overdrive pulley of the alternator?

nemss1

underdrive (smaller) spins slower
overdrive (bigger) spins faster

shnook357

if i get the overdrive pulley for the alternator will i lose any hp?

conan

iTrader: (5)

I think your backwards, smaller pully will spin faster bigger pully will spin slower.

cowboysfan

I thought bigger spins slower and smaller spins faster as far as alternators pully are concerned!!!

conan

iTrader: (5)

Its that way for any pully, if I put a smaller pully on my blower it will spin faster and make more boost.

teke184

iTrader: (5)

question is....
does overdrive always mean bigger pulley, and underdrive always mean smaller pulley?

or does overdrive mean more speed, and underdrive mean less speed?

a smaller pulley on the crank (typically known as underdrive pulley), spins the accessories slower.....including the alt

so in order to get the alt spinning back up to stock speed you need to overdrive it, which in this case means a smaller alt pulley.

confusing


some math:

6" crank, 2" alt = 1:3 rotation
4" crank, 2" alt = 1:2 rotation....alt spinning slower, what we call underdriven generally
4" crank, 1.5" alt = 1:2.7 rotation so the alt is spinning faster, overdriven
4" crank, 2.5" alt = 1:1.6 rotation, so the alt is spinning slower, underdriven

shnook357

so if the overdrive pulley from the alternator is smaller then stock, why did they make an underdrive pulley wich im asuming is biger then stock

nemss1

swapping the alt pulley to overdrive or underdrive isnt gonna have a change in power all that much. wont even be noticeable

conan, im confused now haha. on ASP website, why is the underdrive alt pulley smaller than the stock alt pulley in the pic if it spins faster?

teke184

iTrader: (5)

the smaller alt pulley actually spins it faster

thats why

i think it boils down to what they call underdrive and overdrive....

conan

iTrader: (5)

I'm confused too, I think (teke) is on the right track... what do they concider a under drive and over drive. My thoughts would be to call a small pully a overdrive, because you spin it faster, and a bigger pulley, a underdrive because its spinning slower.

teke184

iTrader: (5)

won't affect hp...

but it will help the charging system...particularly if you run a sound system.

that's the reason for overdriving the Alt with an underdrive crank pulley.