Sail Hatan

Just picked up a bbk underdrive pulley for my cam swap, and it came with the alternator pulley. Car is an auto. Any way I can skip using the alternator pulley? Also I'm gathering its a 77 inch belt with the pulley on the alternator, so what's it with the stock alt. pulley? Thanks guys. I tried a search but got like 12 different options.

mjs1012

iTrader: (36)

I'd use the alt pulley. It'll turn the alternator at a normal rate of speed not slower.

Sail Hatan

Ok, so it says it uses a stock belt? Is that incorrect?

LS-ONE_DAY

I haven't looked into UDP's much but I know for an auto you want to use the overdrive pully for the alternator to keep the battery charged. You need a new different belt with a UDP so I assume you would still need a different size with the UDP/ODP combo. Info I found from a quick search:

SLP pulley response
Powerbond 25% pulley
Brand of pulley doesn't matter I imagine, if they are the same % of reduction.

If you don't want to use the ODP for the alternator your alternative solution to eliminate charging issues would be to raise the idle rpm. I believe 750-850 should be appropriate.

EDIT I just read on WS6Store's product page for the BBK pulley that it uses existing factory serpentine belt so go with that

mjs1012

iTrader: (36)

sounds right. the bigger alt pulley is compensating for the smaller crank pulley

JRENIGAR

iTrader: (37)

^^^ correctamundo...

Sail Hatan

Ok cool. Then I'll just make sure they install both. Does the bigger alt pulley act against the underdrive pulley? Like Rob hp?

JRENIGAR

iTrader: (37)

No, its secondary driven and a bigger pulley will turn the alt slower. Look at it this way: Bigger drive pulley adds speed and drag, bigger driven pulley slows speed and reduces drag. Think mens 15-18 speed bike, works exactly the same way.