Switching Pulley on Alternator

[GCAdidas13 10+ year member]

Audiolife found me a website selling smaller pulleys for alternators.

I currently have a 2.25" pulley, 4 grooves. The car idles around 700RPM, and I'd like to increase it to 900-1000RPM.

2.25" diameter = 1.125" radius. Pi*radius^2 = 3.976 inches. This is the perimeter of the 2.25" pulley

2" diameter = 1" radius. Pi*radius^2 = 3.142 inches. This is the perimeter of the 2" pulley

3.976/3.142 = 1.2656

26.56%

does this mean that the NEW pulley will rotate 26.56% faster than the old pulley?

Thanks

Brian

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[candyman206 10+ year member]

Nope that means you'll end up slowing down the alternator. If you get a bigger pulley it will make the alternator spin faster, but it will rob power from the engine that is hard to notice. But who cares!

 

[ToyTundra 10+ year member]

Nope that means you'll end up slowing down the alternator. If you get a bigger pulley it will make the alternator spin faster,

smaller pulley is what he needs

I would not use a 1.65" pulley. That is such a huge difference in size that you alternator is going to be tearing it up when your car gets moving and may damage your new investment.

 

[ngsm13 5,000+ posts]

Nope that means you'll end up slowing down the alternator. If you get a bigger pulley it will make the alternator spin faster, but it will rob power from the engine that is hard to notice. But who cares!

Are you an idiot?

NG

 

[ngsm13 5,000+ posts]

Audiolife found me a website selling smaller pulleys for alternators.
I currently have a 2.25" pulley, 4 grooves. The car idles around 700RPM, and I'd like to increase it to 900-1000RPM.

2.25" diameter = 1.125" radius. Pi*radius^2 = 3.976 inches. This is the perimeter of the 2.25" pulley

2" diameter = 1" radius. Pi*radius^2 = 3.142 inches. This is the perimeter of the 2" pulley

3.976/3.142 = 1.2656

26.56%

does this mean that the NEW pulley will rotate 26.56% faster than the old pulley?

Thanks

Brian

I would try to 2" pulley, and get another yellow top //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

nG

 

[GCAdidas13 10+ year member]

mr. toy tundra what is your take on a 2" pulley?

 

[ToyTundra 10+ year member]

If they are cheap enough its worth a shot and probably pretty safe.

the numbers say: alternator RPM = 787. May not be enough to notice, but im a alternator nub who hates to be wrong.

 

[GCAdidas13 10+ year member]

If they are cheap enough its worth a shot and probably pretty safe.
the numbers say: alternator RPM = 787. May not be enough to notice, but im a alternator nub who hates to be wrong.

did i mess something up in my first post?

 

[GCAdidas13 10+ year member]

Yeah man you're using the diameter of the pulley as the radius...

 

[ToyTundra 10+ year member]

did i mess something up in my first post?

787 RPM will be approximate alternator speed with a 2" pulley compared to factory 2.25". The note from the picture still applies though

Your using area of the pulley: pi r^2

Circumfrence of the pulley: 2pi*r = pi*diameter

 

[GCAdidas13 10+ year member]

HA

so i was

 

[Moe Lester 10+ year member]

umm, the size of the crankshaft pulley hasnt even been mentioned, the alternator is probably already spinning 2-3 times faster than the actual engine is.

and circumference = diameter x pi

 

[ToyTundra 10+ year member]

umm, the size of the crankshaft pulley hasnt even been mentioned, the alternator is probably already spinning 2-3 times faster than the actual engine is.

read the note in the picture

 

[Moe Lester 10+ year member]

read the note in the picture

well he posted that 787 rpm was correct, so it would seem obvious that he didnt take that part in.

 

[ToyTundra 10+ year member]

well he posted that 787 rpm was correct, so it would seem obvious that he didnt take that part in.

first off that was me. Second, the 787 if for a 2.00" pulley compared to the factroy 2.25".

I agree with you that the crankshaft pulley is key, so I may be so far off i'm wasting my time. On the other hand i dunno if a 1:2 or 1:3 rotational velocity ratio is any closer to real than a 1:1. Maybe in the morning i'll go measure my pullies to get an approximate ratio.