You pull the original crank pulley and put the new smaller underdrive pulley in where the other one was. It doesn't go through the seal but fits inside it and you need a 3 jaw puller and a longer crank bolt to properly remove the old one and install the new pulley. There were instructions on ASP's site but for some reason the link is messed up, email ASP and tell them you need the instructions for the the pulley install.

 

I have a question regarding UD pulleys.

So I had no clue what an underdrive pulley was so I did some google searches.

Some people say okay some people say heck no... supposedly youre running your pump and alternator at a slower speed?

I was wondering if you noticed any diff in engine temp or lights dimming at night when you are at idle???

the reason I'm asking is because I have a stereo with an alpine four channel amp running in my truck. Not insane 2000amps, just one four channel amp maybe running 300 watts... I was also thinking about converting to an electric fan so that would be another item taxing my poor alternator. OF course it will free up even more mass on the engine though...

any thoughts? Would you install an electric fan on your car with the UD pulley?

I think that would be great if I could take the fan clutch off and have a UD pulley.

 

I have a taurus fan and asp pulley and the voltage drops to about 1/4 on the gauge when the fan kicks on and I'm sitting idle. Once the revs get up though it's charging fine. Keep in mind that I'm running a junkyard fan on high which draws about 42 amps, so if you ran it on low or used the flex-a-lite the current draw would be lower. If I was you I'd do the fan first as it typically gives a nice mpg gain of at least 1 mpg then keep an eye on your voltage when it kicks on at idle and decide if you want to do the pulley as well.