O.K. i dont know if this is where to post this.I was a the J.K. today & saw these (pic).On the right are the stock pulleys to the left are the smaller version.Top is water pump, below that is the smog.The smog pulley is from a front drive V8V6 GM car.The water pump pulley is from a GM V6 that was swapped into an isuzzu trooper(yes a trooper).Anyway does anybody have any idea what kind of HP benefit this will give an LG4.I ask only because i havent found a belt yet.Incase someone is wondering.Ive already installed the march power & amp series pulleys.Just thought why stop there.Both pulleys are about 5in across.Stock about 6 inches across.Any thoughts/help/insight appreciated!

 

I dont know if anyone has tried those, but I have heard using underdrive pulleys is worth 5-10 HP at the wheels. Just watch out your battery isnt drained because the alternator is putting out less voltage.

 

The power & amp series pulleys from march takes care of that.The kit supplies a smaller alt pulley.Havent seen any voltage drop at all.

 

Those should actually "overdrive" the accessories. A smaller pulley will spin the accessory faster than a large pulley. It's like a gear reduction setup. A smaller crank pulley and larger accessory pulleys are normally the way to go in order to free up power (less accessory drag). That's why the Power and "Amp" series comes with a smaller alt. pulley. The smaller alt. pulley speeds the alternator up enough to compensate for the smaller crank pulley. Most other underdrive sets come with a small crank/large alt. I'd consider the water pump pulley, though, if you are having flow issues since putting the underdrive set on...

 

I was afraid of that.I did notice the pulley was smaller in the march set.Also that it increases the alt RPMs.So far no overheating or even hotter running engine, but incase i will save that WP pulley.Wouldnt a smaller pulley be lighter though(plus the holes on the SP pulley)helping the engine rev quicker.Long shot perhaps!

 

I have just a crank underdrive pulley I can put on. Would it even be worth the change?

I am not running ac or smog. Just water pump, PS pump and alt.

 

I would think you'd see a better improvement than i did.Since you donta have as many belt driven accessories.I pleased with the small improvement a got from the pulleys.At this point ill take whatever helps,however minute it may be.

 

I'd be leary about underdriving my water pump at all... It already seems a little iffy to do that to a charging system if it's a daily driver, but a water pump?!?!? I don't know man...

But anyhow... Wouldn't a smaller pulley spin the accessory faster, thus creating more drag? Seem's like you would have to enlarge your accessory pulley's to underdrive them, and get a smaller crank pulley to compensate.

I don't know the first thing about underdrive setups though, I'm just trying to tackle this with common sense, and nothing more.

 

Well, the lighter weight may help a little bit... But, you'd still be increasing the parasitic drag on the motor by making the accessory spin faster. I think you would lose a lot more to drag than you stand to gain by the weight. Just my , though.

 

Well this about puts an end to this little project then.Thanks for all the help guys.However if i ever have cooling problems.Ill keeep that smaller WP pulley,just in case!