Now now girls, no need to get in a tizzy.

An Underdrive Pulley would be nice, I'd buy one if it were out. If you're afraid to buy one and put it on your car, thats fine, go cower in the corner, i'll be out driving my xB.

It's not going to kill your car any more than walking across the street is going to get you run over by a bus. Yes it can happen, but it probably won't, even if you have a drool cup taped to your chin.

rpm x watts = who cares, they make them for every other car out there, and the people that use them haven't had many complaints. If you think Scions are made poorly enough that they will explode because you put something after market on them, then maybe you made a bad purchasing desicion. Ford is right down the street.





























geeeesh...

 

That's because of that thing called the "voltage regulator" that, oddly enough, regulates voltage!

Whether the battery is fully charged or not, the VR will put out about 13.4 volts. If the battery happens to be fully charged, its own voltage will be close to 13.4V and it will not accept much current, so the power output (and consumption) of the alternator will be low. If the battery is discharged, it will accept more current and the alternator will provide it unless the current draw exceeds the alternator's capability. If, and only if, the alternator's output limit is exceeded, will the voltage drop.

The alternator's output capabilities drop markedly at low RPM, but usually even this is enough to supply the car's needs and supply constant voltage.

Underdrive pulleys are useful when you are operating an engine outside of normal operating parameters. For example, if you are running at very high sustained RPM in a racing environment you can safely slow down the accessories and still have them work properly.

Another situation is where you have modified an engine to exceed the normal factory RPM limits. The accessories can be damaged by excessive RPM, so your choice is either to slow them down or to modify the accessories to tolerate high RPMs. Most racers choose to slow them down.

Underdrive pulleys can show modest horsepower gains on the dyno, from slowing down the water pump. The other accessories tend to draw whatever power they need regardless of RPM, but the water pump does draw less power at lower RPM.

The big "however" is that the accessories were obviously designed to operate at a particular RPM by some rather intelligent engineers. While a horsepower gain might be available by slowing down the accessories, one must ask why the modification wasn't done at the factory if it was beneficial and harmless. There is no free lunch, and whatever gain in horsepower you might get will probably be repaid in other ways.

Interesting. What school bestows _degrees_ in Auto Maintence?

No, it's designed to provide a constant voltage. The battery's _rate_ of charge depends entirely upon the state of charge of the battery.

[quote="hongs66"]Since the car partially drains the battery to start the engine it must be recharged.

Actually, the amount of energy required to accomplish a normal engine start is rather small, perhaps a thousand joules. A charging current of 5A for 15 seconds will replenish it.

George

 

Some people do care. They're called "engineers", and their caring is why your toyota is so reliable. Shadetree engineering seldom improves reliability.

The same can be said for the "Turbo Fuel Saver"!

Look, there are some situations, particularly racing, where underdrive pulleys may be beneficial. However these benefits do not always cross over to street use. Just because underdrive pulleys are used on some racing cars doesn't mean that you want one on your street car.

George

 

our company RPM OUTLET .COM currently has a underdrive pulley set in development ,sorry no release date yet, but i want a set for my xb so i am pushing the powers that be . maybe if some of you guys are interested you could email or call 281-261-6244 and let it be known that there's a market for this product , thanks for reading .

 

George..
The school is called Ranken Technical Institute. It is located in St. Louis Mo. The degree is called "Associates in Automotive Technology".

As far as the rest of what you said you are correct. However I never said how much the battery gets run down. My scion uses much less battery to get started than my '70 Mustang does.

I wasn't trying to act like I know everything, just trying to make a point that a pully change will not degrated or improve the ability of the alt to charge the battery. It will only change the rpm it runs.