well guys i know they free up hp but they kill the alternator,so u guys only put the crank one.do u still get power just by putting the crank pulley only?or do u need the crank and alt pulley?

 

Your still underdriving the alternator. (Making it turn slower.)

Just not as much. (I think, but I could just be talking out my ***.)

 

and thats with out the alt pulley right .so its still bad well lets wait for someones else response

 

yes puting a crank pulley on, still underdrives all the accessories.

 

ohh okay i see so how long does it take to kill the alt because mines is like 3 months old i bought it new with warranty?

 

heh, ....lets say for instance you are underdriving the alt 1/4 way, so its still turning at 3/4 the correct speed, ...so given the usual life of an alt minus 1/4 the time , thus you have your sum.

did i really just post a formula.....thats funny.

if it makes you feel any better i ran a STOCK alt with a 1500 watt system and it lasted a Damn long time.

also, if you are worried about your alt, get a GOOD battery that hold a decent charge. optima yellow top. expensive as hell though, but hey, if you wanna keep your alt that exrta year. go for it. but chances are you will fry your alt like 3/4 of us have by welding your valve cover to the terminal on the back.
so get the under drive pulleys.

 

I read somewhere it can extend your accessory life by slowing it down. Any truth to it?

(I have a 300watt system and a 105amp alternator and my car eats them.)

 

makes sense, but I'm not sure as to it's truth.

 

not with the alt, the slower it moves the slower it charges, ....therefore making it work longer to charge more, ....so slowing it down hurts, not helps.

 

An alternator doesn't work harder to do anything. It is completely controlled by how fast it spins to achieve full charge, and on most engines, even with underdrive pulleys you have a full charge at less than 1,000 rpm. So every time you go above 1,000 rpm you are just causing it to sping faster but it's not doing anything it wasnt doing at 1,000 rpm. So underdriving it would help longevity in theory. The only thing you are might be putting a drain on is your battery. Lets say somehow your alternator didnt have full charge until 2,000 rpm and you ran your motor at 700 rpm, it wouldn't be making the alternator "work harder," it would simply be putting a drain on the battery because the alternator isnt at full charge.

 

i thought the alt kicked in at 1500 .......heh

and the alt isnt always working at full charge, hence voltage regulator, the alt does work harder when spun slower, no matter what, ....its physics, the faster it moves, the more electricity it produces. the alt does not produce the same amount of electricity at 1500 rpm as it does at 4500 rpm. the voltage regulator , does exactly what its name says.

the slower any acc moves, the more stress thats put onto it.

the strain isnt on the batt, its on the alt. the alt is working harder, to charge the batt due to the fact that a larger pulley is making less rpm, making the alt charge at a higher capacity than its ment to.

 

how is it going to "work harder?" care to elaborate? Most alternators are designed to have a full charge at idle, which is around 600-700 rpm on our cars. When you underdrive them it usually doesn't produce a full charge untill around 1,000 rpm.

 

the voltage regulator kicks varies the amount of electricity that is needed to be sent to the batt, when the charge is needed it sends the electricity. when electricity is being produced slower the alt is haveing to work at a constant rate, thus making it work harder.

 

thats funny, because ive killed a battery , at idle while thumping my system. many times, with a brand new batt AND 140 amp alt. the faster it moves, the more electricity is produced.

 

yes, but regardless wether the voltage regulator is on or off the alternator is still spinning, most of the time faster than needed causing excessive wear.

 

next time you go in your car look at the volt guage. When you are idling it is at around 14 or so right? Now go cruise around and floor it a few times and bring her to redline, the guage doesn't just shoot off the scale. It stays the same. Therefor it is turning way faster than needed. If your theory were correct the whole car would be so overpowered by electricity that it would just fry everything. It can get away with this because of the voltage regulator.

 

heh, people need to learn how to read the entirety of a post and not skim through missing out useful information.

i stated that the voltage regulator varied the amount of electricity being sent to the battery, meaning that your voltage never redlines. it i supposed to always stay at 14.4 unless under massive power drain i.e. headlights, a/c, wiper all on at the same time.

but whatever , you can say you are right, doesnt matter to me.
but under drive pulleys under drive acc. causing more strain.

the stock pulley is made the size it is for a reason, so it doesnt over power the alt, nor under power it. changing this causes stress, more wear, and repercussions. the end.

 

March makes a kit that keeps your alternator at stock speeds. You just have to ask.

 

All I'm gonna say is you will cause a lot more wear overdriving than underdriving.

 

Yeap, power and amp series pulleys

 

Underdriving an alternator would have the sole effect of less potential current output at a given engine rpm. The voltage regulator attemps to always provide a steady voltage, regarless of current draw and alternator rpm. But there are situations where this cannot happen, such as when more current is called for than the alternator can produce at a given voltage. So the voltage decreases instead (since V=IR). If it goes down enough, you won't be charging your battery any more.

Keep in mind that the amp rating on alternators is more of a peak, and is NOT, I REPEAT, NOT, at idle. It is more like 2000rpm. At idle, you are looking at 50% (maybe lower) of peak capacity. So take that into account when doing your calculations for stereos.

To reiterate, SlowMaro, at a given alternator rpm, if it cannot provide the required current, then the voltage will decrease. This is a law of physics. It won't be "working harder." It will just not charge your battery. And BTW, there is no magic number that all voltage regulators in the world regulate to. Not only that, but if you actually tried an accurate piece of equipment (such as a DVM or scanner for the ECM) you'd see that your voltage DOES fluctuate with load, ESPECIALLY at idle.

Extra rpm really isn't a problem. The bearings are pretty good. Try spinning an alternator off the car (or when your belt is off) and you will see what I mean.

In fact, just about the only device I'd really feel ok about under-driving is the power steering pump. Everything else shouldn't be touched, or you will lose effectiveness at idle for all things under-driven (A/C, waterpump, PS pump, mechanical fan and yes, alternator).

 

Thank you for explaining it to him. BTW, by full charge, I meant the required 13 or so volts at idle, not the amperage. A lot of underdrive pulley companys tell you at what rpm you will be at full charge with the amount of undrive they give vs. stock pulleys. The point I was trying to make was you wont be making the alternator work harder by underdriving it. It doesnt have a brain. An alternator doesn't say damnit I'm not up to the required volts so I need to work harder to get there. It doesn't know if it is there or not! The battery just suffers.

 

im still under the impression that a alt varies its potential work load by rpm, and it regulates the output.

so i stand semi corrected. i still say its bad to under drive the alt.
and that making it move slower, causes the batt to not charge enough, making the alt put out full voltage, instead of 1/2 of what its making. and by making it use its pull potential output 24/7, hard the voltage regulator.


putting out more requires more from the alt.

and i have a scanner, ive watched the voltage vrs idle vrs 2000+ rpm, it stays pretty constant as long as im not using anything to pull voltage.

since this *disagreement* could and would go on forever, ill just shut up now. but either one of us are right or wrong, its still bad to under drive the alt. lets stop petty arguing about it and at least agree on that lmao

 

thats a pretty long discussion guys but march does make the power and amp kit for all the high voltage needs like a sound system exc.

 

The electromagnet inside the alternator is only so strong and there are only so many coils of wire in there...there is a limit to what the alt can put out at X rpm, in terms of current flow @ a voltage. It's probably fairly linear. Current flows because there is a potential difference, such as 14V alt output vs ~12V battery. That's why the battery charges. If you ask the alt for 40A for a stereo, and it's spinning at too slow a speed to provide that at 14V, then the voltage will decrease until it can provide the [new, lower] required current, which would be, say, 35A @ 12.5V. Keep asking for more current (by reducing the load impedence) and your alt supply voltage will keep dropping as it tries to supply current. I don't think anything is being "hurt" during this.