Just added a UR pulley to my XRS along with the Magnaflow exhuast,intake ditched the heavy 18sand went back to ultra lightweight 17's, FU%#ING major improvment at the dyno 27h.p.. The pulley added 7h.p.across the board. NOW I NEED ONE FOR THE LITTLE XB any body have any information on one in production?

 

This is practiclly the only mod worth doing as far as easy bolt on power,cant belive nobody is making a pulley kit. Anybody have any info on one in production. My experiances with them on my other cars Matrix XRS/ Mustang show real improvements.

 

yeah same here with my 1989 ford festiva

 

Um what is a pulley in the car for? :oops:

 

Well there is one to drive the A/C belt
The Powersteering belt
The timing belt or chain...whatever this has
And then the Underdrive pulley is the one that is connected to the crank...which another name for underdrive pulley is a crank pulley

 

the AC is already crap...

 

But the pulley he is talking about was the underdrive pulley? How can this create more horsepower? Is it a similiar vain as a lighter flywheel? There prolly isn't any benefit to changing the other pulleys?

LV

 

The reason it allows more power is kinda like a flywheel yea...its lighter and less stress on the engine block.....as for the other pulleys they are mearly for looks only no performance about them

 

also, it's smaller (isn't it?) and as a result it relieves some of the parasidic drag of the other accessories.

 

Yea it tends to be smaller in most cases.....but the key is to keep the harmonic balancer in place

 

There isn't a pulley called the Underdrive Pulley...

Underdrive, like the name implies, under-drives your belt driven accessories... as in making them spin easier (and slower) at every RPM... There is trade off... the air conditioning won't work as good, the alt. wont put out as much (peak will be the same, but peak will be harder to reach since it will be much higher in the RPM range...)

Doesn't seem to be all that great to me!!

 

Gee, you call 7 h.p. on my XRS pointless? I also ran a complete March setup on my mustang for over three years and uh duh....never any problems On an XB/XA even if I only see 2-3 h.p. it would be worth it. And yes im well aware of the counterbalancer issue, so what, Most likley only going to keep the car 4-5 years .

 

if under drive pulleys were out i would buy them......

 

jdaniels, Just a little info. The A/C in every car made is designed to put out max cool at around 1500 rpm. The Alt will put out max power at idle. It is dependent on battery condition, not rpm. I don't think it possible to cause problems with these systems unless you make the pulley about the size of a quarter.

 

Wrong.

Alternators do not put out max power @ idle. By design, the power increases with speed. I have a trade friend @ a local alternator rebuilding shop, and the first thing he does when doing custom winds for more alternator power is put on a smaller pulley.

It's very possible to cause problems, if you have your alternator well loaded already (a lot of people here do).

As for the A/C, I've noticed the car is noticibly cooler when revving higher (Scions, atleast) moving the max-cool rpm up higher wouldn't exactly make me smile.

Now, think about it for a minute, it takes power to make power... so if you're making more power your losing it somewhere else. In this case, it happens to be the accessories.

 

horsepower is simply the release or conversion of energy..

don't forget people.. your water pump gets turned by the crank pulley..

doesn't sound liek a good idea to me to under-drive THAT..

 

Anyone with a multi-gear mountain bike can see first hand the mechanical advantage that an underdrive pulley provides. Check out your pedal/crankset. Notice the triple front chain rings that get progressively smaller towards the bottom bracket? Ever use those smaller gears to help you climb up a long steep hill?

The front gear is your drive pulley. The amount of work needed to turn the rear wheel depends on a lot of variables like how steep the inlcine, how much speed you're trying to maintain, how much drag, etc A steep road requires more effort than a flat road. By dropping into a smaller front gear, you can help the pedals turn easier, although you don't climb as fast because your rear wheel doesn't spin as fast for every pedal revolution. You get a mechanical advantage in that gear choice that reduces the amount of work required to turn the pedals. But you'll need to turn the pedals more times to climb that hill than if you were in a bigger gear. Add up the total amount of work needed to get to the top, and it's going to be about the same whether you're in a gear that is hard to push but climbs fast, or is easy to push and requires you to pedal a lot.

In a belt driven automobile system like the AC or alternator, a modest amount of work is needed to turn the mechanism and produce dc power or compress refrigerant, like a slightly steep hill on your mountain bike. An underdrive pulley will drive the AC and Alternator at a slightly slower speed, requiring the engine to work less. They turn slower, like the rear wheel of the bike going up the hill.

That means they'll produce less compression or power at slow engine RPMs. But these systems reach their peak fairly low in the engine's operating range. So they will still output at their designed level, but at a higher engine rpm than with a standard sized drive pulley. And like the hill climb, they will still require the same amount of power to generate their peak output levels.

In the end, you free up a percentage, not all, of horsepower that was turning the AC and alternator and can add that power at the rear wheels. How much power? That would depend on what the full load requirements for the AC compressor and the alternator are.

A couple of rough reference points- my shop compressor requires a 7 horsepower electric motor to create 175 psi at 10 cfm. That's a lot more compression than what would be in our AC systems. My back-up generator uses a 5 horsepower gas engine to turn the generator and produce 4000 watts of power. That's a lot more current than is needed to charge our batteies and run our sound systems and cold cathode lights. I'd guess that the combined full load requirments of the AC and alternator in an xB would be in the range of 5-8 horspeower total. That amount of horsepower is going to be needed to operate these accessories at full output regardless of how fast you drive the pulley.

If you reduce the drive pulley in size by 50% you'll save 2.5-4 horsepower at some point in the engine rpm range, likely early on when there is low load requirements from the accessories. If the peak alternator or AC output is reached at a point below max engine rpm, you'll simply get to that maximum output level at a higher engine rpm.

I believe an underdrive pulley will give you a little seat of pants performance boost, but once you're into the full operating output levels of the AC and alternator, your power improvements will disappear.

 

1HP = 746 WATTS

how many amps is your alternator?

100AMPS as an example

Watts = AMPXVOLT

so.. 100AMPS (full Load) X 14V (FULL VOLTAGE) = 1400WATTS

let's say a 80% efficiency on the alternator (extremely low efficiency, but for teaching purposes) this puts your Wattage(HP) requirements at 1750W (2.34HP)

so.. the alternator at full load (minus drag) is gonna pull MAYBE 2.5HP..

that is considering your battery is dying, you're running all your lights, accessories, your system with a huge amp...

2.5HPTOTAL..

the water pump is where it's at people...

i could give you HP requirements for this as well, but because it's not a positive displacement pump, it's gonna be a bit harder..

 

jdaniels...Do me a favor, go out to your car, turn on the lights and leave it for about 1 hour. Then go back out with a volt meter. Attach the meter to the battery and start the car. Let the car idle. It will put out as much volts as possible until the batery is charged up. You can do what ever you want with the rpm. It will make VERY little if any difference. I'm glad you asked your friend, but I also worked in the trade and have a degree in auto maintence. The alt is designed to charge the battery up as fast as possible. Since the car partially drains the battery to start the engine it must be recharged. The alt doesn't know if you will be driving at hwy speeds or sitting at an idle, driving for 6 hours or 6 min. The major determining factor of alt output is the number of windings, rpm has very little to do with it.

 

The voltage may stay fairly constant, but the amperage goes up. Please stop acting like you know everything.