i know the UD pulleys slow down the accs. , would i need to use a OD pulley on the alt. if i want it to spin at normal/faster speed? reason i ask is i have a DC power 270xp alt. and high powered stereo system. so i need it to spin at normal speed if not faster.. ( produces full output 270amps @ 2000rpm)

 

I am running a powerbond UD pulley and an ASP OD alternator pulley. It will run the alternator at the same speed it did stock this way.

 

cool thats what i was thinking but wasnt sure

 

Although we have many customers run underdrive crankshaft pullies without and od pulley on the alternator, I would suggest running the overdrive alternator pulley anytime you switch to an underdrive crank pulley.

 

Since the whole idea if running an U/D pulley is to reduce the drag from the turning of the water pump, p/s pump, a/c, and the alternator; aren't you losing a large part of the benfit by spinning the alternator back at it's original speed?

 

You will lose some benefit, but you're also spinning the AC, water pump, and power steering slower.

I did this swap and replaced the stock 105A alternator with a 145A alternator and didn't swap the alternator pulley. I have e-fans and a single 800W sub, no issues so far. The lights don't dim at all even at idle.

If you know the OD of the crank and alternator pulleys, and have the current output vs. speed chart of the alternator, you can easily calculate what power the alternator is outputting.