Definition of "UnderDriven"

[NuclearBacon]

So ive seen pulleys labeled as Underdriven and Not Underdriven.... What exactly does that mean? Is it talking about a smaller diameter size to increase rotational velocity? or am i so far off.... yeeeah....

I'm learning every day, so i thought i'd pick the brains of the wise and mighty thanks for putting up with my Q's.

[DLC]

Underdriven means that they are smaller in diameter than the stock pulley. This means that the accessories, AC, PS and Alternator, do not turn at the same speed as they would otherwise, if my understanding holds.

Lightweight pulleys with the stock diameter size, or nearly so, let you use stock belts and won't cause problems from low alternator output and power steering and AC pressure.

[NuclearBacon]

So why would you want underdriven anything? besides making your alternator not charge and your power steering whine and be upset...

just for weight? doesnt seem like its a good idea....

[Legacy777]

Think of a mountain bike. When you're in the small gear in the front it's a lot easier to pedal. You have a gearing advantaage, and it doesn't take as much torque to pedal.

The same applies here. If you run an underdriven crank pulley, the motor doesn't have to work as hard to power the accessories. The down side is they don't rotate as fast.

[NuclearBacon]

that makes sense... just doesnt seem like a very good... execution of power ....release....

[skid542]

The biggest reason to go with a underdriven crank pulley is if you have done head work such that you have raised the redline signficantly. If you have a stock motor that reds at 6.5k rpm and now you have a red of 9k rpm, your power band has shifted and without an underdriven pulley you could be over driving the p/s pump and such.

For a stock motor, you don't really want one, but a lightweight stock diameter pulley can/will make a difference.

[NuclearBacon]

ahhh ok, see i learn. Thanks!! you guys should open a school

[SILINC3R]

yea you should then you can show me first hand how to use the quote, ebay link, picture stuff.

anybody bought the pulley set from reason. i might get one but not sure.

[NuclearBacon]

the pulley i'm going to be picking up is a perrin lightweight NON-UNDERDRIVEN crank pulley. its 4 lbs lighter then stock, and doesnt have the rubber piece sandwitched in the middle like our cast pulleys do. (harmonic ballencer?) I'm getting one used at a killer price (about $35) they retail for about $100 and directly from perrin, its $150.

i would be happy to write up a small tutorial on how to post simple things and do some of the more basic features on the forum. posting pictures, linking to pictures... pm me if you ever have any questions... i'm on here WAY too much