ToxicFormula

What exactly does an underdrive pulley do and what does it accomplish?

orangeapeel

iTrader: (18)

It helps with parasitic loss from other accessories run by your belt like AC and alternator for example.

CBX

Smaller diameter pulley= lower gear, requiring less HP to turn your alternator, PS pump, water pump and A/C compressor. The result is more HP left over for the drivetrain to use.

ToxicFormula

so does it go in the place of the balancer pulley?

And I've heard that some pulleys don't provide enough electrical charging at idle

dschmittie1

iTrader: (64)

ususlly they don't provide enough charging in auto cars(they have a lower idle speed) so people with autos can get an over drive pulley for the alternator

CBX

Yes it replaces the stock crank pulley (balancer pulley). Can't say as far as charging problems as I have yet to fire mine up with the new pulley. Although, I have heard a lot of people say that they have no charging issues.

Kyle C

M6 car here, no charging issues. Didn't notice any SOP power increase either but it has to help some.

ToxicFormula

I know I'm bringing back an old thread but I'm getting ready do buy an underdrive pulley and I was wondering if it was necessary for me to buy an overdrive pulley for my alternator since I have an auto. I was also wondering what brand pulley(s) would be recommended. Thanks

jmm98LS1

iTrader: (28)

I've got no charging issues with mine, I'm an auto too. I didn't buy the overdrive alt. pulley either. Just buy it already!!!!

Ωmega

iTrader: (28)

The overdrive pulley isn't necessary, but if you run other accessories (radaer, system) you may want to consider it. Just keep in mind that the overdrive will decrease the HP gain you see.

orangeapeel

iTrader: (18)

If you are a stereo person, then it may be worth your while. Otherwise I would just install the UD and be done.

v8hunter

iTrader: (2)

I didn't need an alternator pulley either. I wouldn't worry about it unless you have a big stereo. I have a SLP ud pulley...others here speak well of the powerbond and asp.

moeZ28

iTrader: (7)

most people with cams have their car tuned to idle over 800rpms and from what i have heard, under 700 or 800 rpms is when you dont get a good charge from an underdrive pulley, but if you are idling over 800 rpms, you would be charging just fine. i cant remember where i heard this, may have been on a previous discussion here, but i know a few people with them and they have not had any problems. i bought a powerbond 25% underdrive pulley for my new motor and it is a very nice piece of work. i got it from TSP for like $195 plus shipping? something like that.