could I find a cheap UD pulley

[no1kicker]

I want a UD pulley and was wondering if you guys knew if most GM crank pulleys were the same size. I thought if some were smaller it would be possible to go to a junkyard and swap one and not have to spend the $100 for the new one. Just a thought.

[Robby1870]

I think 2.8/3.1/3100 are the same size, Series I 3800 is bigger than those, and Series II 3800 is WAY bigger because the crank is not internally balanced. Another problem I would see is that with other GM crank pulleys (non FWD and non W-body), the belts maybe different widths, so the pulley from those wouldnt work. But, in all honestly I dont know, and actually have never thought of it, but its a good idea. Just make sure if you find a motor with one that will work, make sure the crank is internally balanced, like the 2.8/3.1/3100/3.4

 

Robby

[Bowtiekid]

the crank pulley is the same size (same exact pulley) on the 2.8/3.1/3100/3400 (Approx. 6" dia). The 3.4 DOHC is also internally balanced, but it uses a different setup.... they have a seperate pulley that you can unbolt from the damper.

[NeverSayDie]

sounds like you're thinking sdrawkcab dude. to underdrive your accessories you need a larger pulley, not a smaller one! just a tip

[Bowtiekid]

Not if you are talking about the crank pulley. The driving pulley needs to be smaller if you want to under drive it. the driven pulley needs to be bigger if you want to do the same.

[NeverSayDie]

thinking backwards i was, wiser than me you are

[lukee1982]

so if you were able to find bigger pullies for your alt powersteering water and air compressor or some would much horsepower be gained?

[NeverSayDie]

you really don't gain any, it just frees up power you already had, but were losing to drag. probably 5 whp max

[Bowtiekid]

you have to look at it as a percentage (or a ratio between EACH accessory and the crank)... if you wanted all your accessories to run 20% slower, then you would need pulleys that were 20% bigger on all your accessories. If you look at the water pump and p/s pump.... there isnt much room to go any bigger. (on the LQ1 at least). You also cant get larger a/c pulleys. You can get the same 20% under drive with ONE crank pulley since it drives all the other pulleys. You also save weight since its smaller VS adding mass to all the other pulleys. In the end, it is much simpler to use a smaller crank pulley. The results would be the same (if you ignore the fact that you add weight with larger pulleys), but one way is much simpler.

[Bowtiekid]

as far as not gaining hp... no it doesnt make the engine more efficient at making power. It just uses it to turn the wheels instead of turning the accessories as fast. The FFP pulley actually shows a REAL (on a real chassis dyno) gain of over 10hp AT THE WHEELS at about 5000 rpm.

[NeverSayDie]

ow! i was burned again! we have now established that i need more education on the matter of underdrive pulleys!