Do Pulleys affect the Altenator?

[BassiKLowZ 10+ year member]

Ive never heard of this. . . but someone brought to my attention that lightened pullies and under pullies henders your system.

According to the guy, he used AEM pulleys as an example. . .

...they are lighter...but the accessory pullies (like those included in the aem kit) are oversized so it takes less power to make them spin. that is why people with systems complain about getting them because your alternator will actually be getting less power.

Is this true? And does it make for a substantial loss? Any help is appreciated.

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[n2audio 5,000+ posts]

He's right - that's the point of underdrives, but I don't know how substantial the change would be. I don't feel like doing the math to find out. I would guess the biggest difference would be at low rpm's and at hiway speed there wouldn't be much difference at all.

 

[Trixter 10+ year member]

A smaller pulley will produce higher amperage, while a larger one will produce less. The smaller the pulley, the faster the alt. will spin. On the flip side of things, the larger the pulley, the more rpm's it takes to turn it, resulting in less hp. (So I guess small is better in both ways.)

..."are oversized so it takes less power to make them spin." - wrong

The larger they are the more power it will take form the engine to make it spin and the less power it will put out.

..."that is why people with systems complain about getting them because your alternator will actually be getting less power."

I think he means to say it will actually be putting out less power. (If the larger ones are used that come w/ the kit.)

 

[BassiKLowZ 10+ year member]

So basically, if the pully is the same size or smaller, but just "lightened" it shouldnt effect the output of the altenator?

I dont really know how much bigger the pullies are in those kits over or under stock. . . something for me to look into. . . i appreciate it fellaz. . .take care

 

[n2audio 5,000+ posts]

Trix - you're contradicting yourself

Originally posted by Trixter A smaller pulley will produce higher amperage, while a larger one will produce less.

correct.

The smaller the pulley, the faster the alt. will spin.

correct again.

On the flip side of things, the larger the pulley, the more rpm's it takes to turn it, resulting in less hp. (So I guess small is better in both ways.)

This is confusing - if the pulley is larger, the speed of the alt shaft will be reduced at a given rpm vs. the speed of the shaft with the standard pulley = less current being produced by the alt = less hp being bled from the crank. (Law of conservation of energy)

..."are oversized so it takes less power to make them spin." - wrong

Trix - this is the point of under-drive pulleys - it's a true statement. Under drive pulleys are oversized so they revolve fewer times per revolution vs. a standard sized pulley - any component with an under-drive pulley would be doing less work than with the standard sized pulley resulting in less hp being drained off the crank.

The larger they are the more power it will take form the engine to make it spin and the less power it will put out.

It will absorb less power and put out less power - again, conservation of energy.

..."that is why people with systems complain about getting them because your alternator will actually be getting less power." 

I think he means to say it will actually be putting out less power. (If the larger ones are used that come w/ the kit.)

Right.

 

[tommyk90 5,000+ posts]

Now i'm really confused. Which pulleys come with an under-drive kit? Larger ones than stock or smaller ones than stock?

Edit: 900 posts. Whoo, hoo.

 

[splfreak2003]

putting a smaller pully on your alt will alow your alt to produce more amperage in idle, due to it being able to spin faster or make quicker rotations.... thats about it...

 

[Randy Savage 5,000+ posts]

Originally posted by splfreak2003 putting a smaller pully on your alt will alow your alt to produce more amperage in idle, due to it being able to spin faster or make quicker rotations.... thats about it...

Yep.

 

[tommyk90 5,000+ posts]

Originally posted by splfreak2003 putting a smaller pully on your alt will alow your alt to produce more amperage in idle, due to it being able to spin faster or make quicker rotations.... thats about it...

Does it free up any horsepower?

 

[n2audio 5,000+ posts]

Originally posted by tommyk90 Now i'm really confused. Which pulleys come with an under-drive kit? Larger ones than stock or smaller ones than stock?

Under-drive pulleys are larger in diameter than stock pulleys. If you put an under-drive pulley on your alternator it will increase hp to the wheels a teeny-tiny (un-noticable) amount, but decrease the current available for electrical components.

 

[tommyk90 5,000+ posts]

Originally posted by n2audio Under-drive pulleys are larger in diameter than stock pulleys. If you put an under-drive pulley on your alternator it will increase hp to the wheels a teeny-tiny (un-noticable) amount, but decrease the current available for electrical components.

Fl_lCK that. I need all the power i can get from my alt. I'll have to get a new one soon if i stick with my plan (check the sig).

 

[taylor 10+ year member]

a smaller pulley on an alt is bad for highway use, it will sound like your alternator is going to take off cause it will be spinning so fast...

 

[BassiKLowZ 10+ year member]

wow, i learned alot here. . . i appreciate the replies fellaz