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Underdrive Serpentine Pulleys

santana

santana

1/2 ton status
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Who here runs these on their rigs?

It's supposed to free up 15-20 HP at the rear wheels while slowing down the revs on all accessories with out affecting performance.

What are the pros and cons of these?

LMC has the set for under $100, Seems well worth it if you can pick up a bunch of ponies eh?..

I'm considering going with these unless there are downsides to it.
 
The only draw back I can think of would be with the alternator. If you are taxing the alt with things like off road lights and other accessories that draw a lot of juice, then under driving the alt may not be a good thing.
 
Don't forget about the power streering pump. I want as much help as it can give me when i'm trying to negotiate a trail. The bigger the tires are, the more you need the pump helping.
 
I run UD pulleys on my Mustang. They only seem to help a little at the top end. Dont believe the manufactures hype about them. Yur lucky to see 10 Hp gain on the top with UD pulleys. They really are ment for drag racing in a light car where you are trying to squeze every tenth you can out of your hot rod. The only reason I run them is I got a set for 25 bucks on E bay.
I would not run them on a 4x4 truck. I really dont think they would help a heavy truck at all.
Besides you would have probabally charging issues at low RPMs. like when crawling on the trail.
Cant really run a powerful stereo, lights, or other heavy power robbers at low rpm. Also they put more strain on the battery.
Doubt you would see any power gains on a heavy truck. Save your money and use it for something better. Like gas:D
 
we use them on the circle track car just cause they have deeper grooves and when the belt spins a little slower it is less likely to be thrown off(though it still happens when revving 7k for a while). I wouldn't run them on a daily driver or a trail rig. A street machine or drag racer I'd consider it.
 
a smaller pulley would reduce the current, not increase it. Same with pump flow, smaller pulley reduces flow.
 
wrong. Smaller pulley on the alternator the alternator will spin faster. Faster = more power. Bigger pulley is the underdrive setup and that spins slower thus producing less power. Samething goes for the waterpump, smaller pulley faster it spins. Think ring and pinion. The pinion is the smaller gear and spins faster.
 
Smaller pulley on the alt should make it drive faster. Smaller pulley = less circumference = more turns per given length of belt gone round.
 
yeah that is true but I'd just run a smaller alternator or power steering pulley. Wouldn't be surprised to lose power with a smaller pulley, less circumference=less leverage.
 
things get backwards in my head too, it sucks when you are so sure then you realize, damn I was way off.
 
I had underdrives on my BBF in the old truck and didn't like them. Amps sucked at idle and the 40's were hard to turn at a stop on the trail. Only reason they were on there is they came with the truck and, being aluminum, looked cool!
 
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