What do you know about Under drive Pulleys???? HELP

[AMBULLDOG2002]

I bought and installed a set of JET pulleys today. A friend of mine was telling me how much he felt a difference in power, so I figured I would try it.
After installing them I didn't really notice much of a difference at all. The crank pulley is smaller and the alt pulley is slightly bigger than stock. From what I have read this slows down the alternator, what I don't rally understand is how this works and why. The only significant difference I notice is dim headlights and a underpowered heater blower motor, all until I give it some gas and built RPM. I under stand why it does this but my main question is if I use the JET crank pulley and go back to the smaller alternator pulley, wouldn't this increase my alternator output. I may even just go back to stock because like I said I don't really see much difference. Any ideas or help is appreciated.

[HenryJ]

Go back to stock. First. You need the rpm to power the borderline power steering pump. Look up the thread on the power steering pump upgrades.
Second, you need more alternator rpm, not less. Stock is already a little too slow to meet demands.
Check out the bigger alternator thread. Sorry that one is looong. Moral of that story is to upgrade to the AD244 alternator , a slightly smaller than stock pulley and be happy ever after. Best $50 you can spend at the salvage yard.
If you want to gain a little throttle response and control over the temperature. Seek out the LS1 e-fan conversion. That eliminates the drag of the stock clutch fan. That said the stock clutch fan is pretty good. If you're in a hot climate and tow , I stick with it.

Summary: underdrive pulleys are not the answer for these trucks as daily drivers.

[green02crew]

I've been running underdrive pulleys for years now. Daily driver and all. Here's the breakdown on them. There is some power increase. No power steering issues at all and no alternator issues if the pulley is correct, yours obviously is not. It should be much smaller than stock, the smallest you can fit in fact. The negative issues are really only two: the cooling isn't as efficient. I've never overheated but it also isn't very hot up here in Northern NH. I do tow often though, when I use my truck it has loads or is towing every time. Second issue is the only real issue. Belt slippage. Pulleys I have are aluminum. Goodyear Gatorback is the only decent belt and they start to slip after about 20k miles. Normally the belt should last longer than that.

Is it worth the price? No. Am I going to go through the effort to put it back to stock? No. You need to make a change for sure as the alt pulley should be smaller than stock, not larger.

[AMBULLDOG2002]

Just changed the pulleys back to stock. So needless to say, if anyone is looking for an under drive pulley kit let me know because it's going on eBay tonight.
Thanks again for the education on how the pullies work and what they do.

[F9K9]

Just changed the pulleys back to stock.........

Good for you! Post them on CL, as well. When performance increases seem to be to cheap or to easy to believe..................they aren't what they seem to be.

[border man]

Speaking of pulleys, are they adjustable at all? Since getting my engine rebuilt, I've gone through three belts. The power sterring pulley seems to be slightly out of alignment to my eye. The belts keep losing one of the groves to where it rides all the way flush towards the engine on all the pulleys and towards the front on the PS pulley. The pump seems fine, no play when the belt is off. Anyway tho shim the pump/pulley forward?

[HenryJ]

They should not need adjustment / alignment. More than likely something is work. The tensioner assembly can wear and allow that pulley to ride on an angle. Bearings in the idler and tensioner pulleys wearing out and becoming loose are the most common. Take the belt off and check them. A wiggle and a spin should find the culprit. Check the waterpump and alternator too.