Underdrive Pulley

[Admin]

I've been wondering about this with A4s. Now if you get a March or ASP I know you have to get a belt tensioner, Katech has one. But, the big question is do you have to get an overdrive alternator pulley along with the underdrive pulley. This guy on LS1tech says you have to for the A4s or you won't see a power difference, anyone familiar with this subject...

There's probably a lot of guys out there who just slap on an underdrive pulley for $200 and end up losing power because they didn't put the overdrive alternator pulley on.

here's a link http://www.ls1tech.com/forums/showth...=471979&page=2

[Admin]

Everyone that I have talked to about this seems to be clueless...

[ta12sec]

why would u lose power smaller pulley = less mass and easier spining i dont see how you would lose power

[Ta Jay]

i remember sumtn about losing voltage. double chek it

[ta12sec]

voltage at idle will decrease, overall output shouldnt be affected,
overdrive alt pulley would cure that

[DanO]

This isnt rocket science....

you put an underdrive pulley on the crank.. it spins everything slower relative to crank speed (less tangential velocity at a smaller radius and same RPM)


If you want to maintain the same ratio of crank speed to alt speed you will need to add an overdrive pulley to the alternator...

its basic math


And yes, you affect every accessory that is driven by the belt, "how much" is known by the engineers who chose the stock pulley sizes. You'd have to know more info about each accesory to say for sure.. or you can "guess and check" like 99.9% of people.

[Ta Jay]

o great here comes the resident engineer to make sense of everything '''%

[Ta Jay]

yah wherd u go to school Mr.engineer?

[WishIHadACamaro]

oy.