Downside to an underdrive pulley?
Downside to an underdrive pulley? I'm sure this has been covered, but I have been searching and found nothing. I am looking to buy a 25% UDP and I was wondering if there is a downside to them, like putting a strain on engine components? Also while Im asking noob questions, do I need a different belt if I buy one?
Thanks for the quick reply 
Dimmed lights? If thats all, then Im sold. I heard that it burns out some of your components a lot quicker. Anyone dyno there car before and after a Underdrive pulley?
Dimmed lights? If thats all, then Im sold. I heard that it burns out some of your components a lot quicker. Anyone dyno there car before and after a Underdrive pulley? i bought mine and needed diff belt(s)? and have not had any dimming of the headlights. the oil temp does like to raise up when i get on it but I have heard thats normal. the underdrive pulleys don't add too much HP it's a slight difference but nothing "OMG"
Staging Lane
Joined: Jun 2008
Posts: 60
Likes: 0
From: A bit south of Sacramento, CA
You will find that when idling your voltage will drop to about 8-9 vdc. This will appear as dimmer lighting, slower heat/ac fan speed and slower turn signal blinking. These symptoms will disappear as soon as you give it some gas and the rpm's get above 1000.
Now as far as premature damaging of components, here is what happens. When the voltage source for an item drops the amount of current draw increases. This will translate into higher temperatures in the wiring and the item being run. Heat will shorten the life of most anything electrical, by how much will depend on each individual item.
I have run an underdrive pulley for over 120K miles. So far, I still have the original alternator, dash lights, headlight motors, heater fan. Only electrical items I have had to change are window motors (no surprise here), headlights (they all go eventually) and the ignition switch (now this one i suspect as possibly being due to the lower voltage).
I say this because the plastic near all the terminals was melted and the contacts were pitted. Now to be fair there was 142K miles on the switch and it may have just gotten old. But being an electronics person it did look to me like a high current draw type damage. It was an easy fix and cheap too.
Dyno test showed an 8 HP gain, it was the first modification done to the car.
Now as far as premature damaging of components, here is what happens. When the voltage source for an item drops the amount of current draw increases. This will translate into higher temperatures in the wiring and the item being run. Heat will shorten the life of most anything electrical, by how much will depend on each individual item.
I have run an underdrive pulley for over 120K miles. So far, I still have the original alternator, dash lights, headlight motors, heater fan. Only electrical items I have had to change are window motors (no surprise here), headlights (they all go eventually) and the ignition switch (now this one i suspect as possibly being due to the lower voltage).
I say this because the plastic near all the terminals was melted and the contacts were pitted. Now to be fair there was 142K miles on the switch and it may have just gotten old. But being an electronics person it did look to me like a high current draw type damage. It was an easy fix and cheap too.
Dyno test showed an 8 HP gain, it was the first modification done to the car.
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You will find that when idling your voltage will drop to about 8-9 vdc. This will appear as dimmer lighting, slower heat/ac fan speed and slower turn signal blinking. These symptoms will disappear as soon as you give it some gas and the rpm's get above 1000.
Now as far as premature damaging of components, here is what happens. When the voltage source for an item drops the amount of current draw increases. This will translate into higher temperatures in the wiring and the item being run. Heat will shorten the life of most anything electrical, by how much will depend on each individual item.
I have run an underdrive pulley for over 120K miles. So far, I still have the original alternator, dash lights, headlight motors, heater fan. Only electrical items I have had to change are window motors (no surprise here), headlights (they all go eventually) and the ignition switch (now this one i suspect as possibly being due to the lower voltage).
I say this because the plastic near all the terminals was melted and the contacts were pitted. Now to be fair there was 142K miles on the switch and it may have just gotten old. But being an electronics person it did look to me like a high current draw type damage. It was an easy fix and cheap too.
Dyno test showed an 8 HP gain, it was the first modification done to the car.
Now as far as premature damaging of components, here is what happens. When the voltage source for an item drops the amount of current draw increases. This will translate into higher temperatures in the wiring and the item being run. Heat will shorten the life of most anything electrical, by how much will depend on each individual item.
I have run an underdrive pulley for over 120K miles. So far, I still have the original alternator, dash lights, headlight motors, heater fan. Only electrical items I have had to change are window motors (no surprise here), headlights (they all go eventually) and the ignition switch (now this one i suspect as possibly being due to the lower voltage).
I say this because the plastic near all the terminals was melted and the contacts were pitted. Now to be fair there was 142K miles on the switch and it may have just gotten old. But being an electronics person it did look to me like a high current draw type damage. It was an easy fix and cheap too.
Dyno test showed an 8 HP gain, it was the first modification done to the car.
I have an ASP crank and need different belts!!
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Staging Lane
Joined: Jun 2008
Posts: 60
Likes: 0
From: A bit south of Sacramento, CA
I aint got college but I do have 5 years OJT on helicopters (Afghanistan and the like). Not to mention everybodys cars that have elec problems. Good to know I ain't the only one who thought it was a good thing to have around cars. Dont know anything about a cam but put a wiring diagram there and I do alright...
You can get a over drive pulley for the alternator to help with low rpm voltage drop. This is from Thunder Racing >>>>>>>>>>>>>>>>>>>>>>
Overdrive Alternator Pulley - Recommended for automatic cars to help bring alternator speeds back to near stock levels without sacrificing too much horsepower. Extremely important for vehicles with high accessory drag such as cars with lots of stereo modifications.
Underdrive Alternator Pulley - Recommended mainly for track use. Not recommended for daily street use due to low alternator charging.
Alt PulleyPulley Part #AC Belt #Access. Belt #
Overdrive49-54012011-378K411-755K6
Underdrive49-54008411-378K411-770K6Stock -11-378K411-760K6
Overdrive Alternator Pulley - Recommended for automatic cars to help bring alternator speeds back to near stock levels without sacrificing too much horsepower. Extremely important for vehicles with high accessory drag such as cars with lots of stereo modifications.
Underdrive Alternator Pulley - Recommended mainly for track use. Not recommended for daily street use due to low alternator charging.
Alt PulleyPulley Part #AC Belt #Access. Belt #
Overdrive49-54012011-378K411-755K6
Underdrive49-54008411-378K411-770K6Stock -11-378K411-760K6
Last edited by Randy WS6; Aug 4, 2008 at 07:39 PM.
Nobody's mentioned this one yet. With an automatic ONLY, you will need the overdrive alternater pulley. Only with the automatics do little annoyances arise such as dimming headlights and that type thing. If you've got a 6spd as I do, then you won't need the overdrive pulley for the alt and your electronics will be just fine. My underdrive pulley only added to my lack of traction
. I just bought another "fix traction issues" mod recently though I should be able to put my full bolt on power down on the track nicely now
. I just bought another "fix traction issues" mod recently though I should be able to put my full bolt on power down on the track nicely now 
Well I was going to get one at one point. But my friend took his turbo car out on its maiden voyage to the track and every pass was getting faster and faster till he got it to a 12.0 and than the car died in the staging lanes. It had a dead battery. He switched back to the stock pulley and never had a problem sense. Thats the sole reason I wont get one is because when I'm shooting for 11's I know its gonna come back and **** me 
yea that was me, first passes with old kit on stock motor with 5 psi. i was very pissed, so close! However, to put the puzzle together, i had my lights on, all guages inside had lights, car was sitting in 3rd as i was up next, had a scavenge pump running, etc. So all accessories plus more were running so having the underdrive pulley didnt not supply enough at the time and killed it.
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