ud pulley

**kenro23** · 04-06-2011, 01:48 PM

if i were to put a ud pulley in my car, is there a need for an od pulley also? please explain why or why not. also, where is a good website to get one or both of these items

**jiveass** · 04-06-2011, 01:56 PM

referred to this post

http://www.ls1.com/forums/showthread.php?t=75881

**redbird555** · 04-06-2011, 02:51 PM

^^Thats not really what he asked for so I'll give it whack. Underdrive pulleys are worth anywhere between 7-12hp in the power band and do help the car rev quicker so its not a bad bolt on. Anyway an underdrive pulley slows sown all the accessories because it is externally smaller by 10%-25% by doiing this the alternator will turn slower and not produce as much voltage and the water pump etc will all run a little slower. Is it enough to cause any issues? No most likely not mine is completely fine and so are all the cars I've researched the people who have issues with it are people who run huge sound systems or some other form of large power draw at idle where the alternator cant keep up. If you dont have any huge power drawers like that you'll be fine.

**jiveass** · 04-06-2011, 05:43 PM

Originally Posted by redbird555

^^Thats not really what he asked for so I'll give it whack. Underdrive pulleys are worth anywhere between 7-12hp in the power band and do help the car rev quicker so its not a bad bolt on. Anyway an underdrive pulley slows sown all the accessories because it is externally smaller by 10%-25% by doiing this the alternator will turn slower and not produce as much voltage and the water pump etc will all run a little slower. Is it enough to cause any issues? No most likely not mine is completely fine and so are all the cars I've researched the people who have issues with it are people who run huge sound systems or some other form of large power draw at idle where the alternator cant keep up. If you dont have any huge power drawers like that you'll be fine.

thats pretty much most of the info in the link i provided...

**pajeff02** · 04-06-2011, 06:03 PM

KY Speed is a site sponsor and has pretty nice prices and shipping deals: Underdrive Pulley

**kenro23** · 04-07-2011, 11:38 AM

well, i do have one of those systems like you are talking about. i reasarched it yesterday and i see that with a high need stereo, you need the od pulley for the alternator. if i were to do both of the pulleys, what would be the outcome to hp and juice for the stereo, lights, etc...

Originally Posted by redbird555

^^Thats not really what he asked for so I'll give it whack. Underdrive pulleys are worth anywhere between 7-12hp in the power band and do help the car rev quicker so its not a bad bolt on. Anyway an underdrive pulley slows sown all the accessories because it is externally smaller by 10%-25% by doiing this the alternator will turn slower and not produce as much voltage and the water pump etc will all run a little slower. Is it enough to cause any issues? No most likely not mine is completely fine and so are all the cars I've researched the people who have issues with it are people who run huge sound systems or some other form of large power draw at idle where the alternator cant keep up. If you dont have any huge power drawers like that you'll be fine.

**Ls_won** · 06-20-2011, 05:13 AM

sorry to resurect an old thread, but on my 98 cobra i have a under drive pulley, and started lacking the volts i needed with just one 12 inch sub. I now installed a overdrive pulley onto the alternator but also upgraded to a 220 volt alternator. Overdrive pulleys do help thats for sure.

**Smittro** · 06-20-2011, 05:29 AM

UD good for drag racing, for street and systems, eh not so much.

OD good for Stereo systems and additional rotor com wear.

Take your pick.. I'd go with stock pulley and a higher Amper Alt, and maybe a good capacitor..imho