M5x/S5x Underdrive pulleys

[CorvallisBMW]

CRANK PULLEY SOLD. PS PULLEY STILL AVAILABLE FOR $50

Made by Orthodox Racing (http://www.unorthodoxracing.com/). Used for only 2 months, they're in perfect shape, if a little dirty. The belt grooves are flawless, no nicks, dings or defects of any kind. PS pump pulley measures 5" (12.6cm)
* measured by dividng the circumference by pi

[CorvallisBMW]

wednesday bump!

[tonytony]

that's odd that it comes with the crank pulley and not the water pump pulley

[CorvallisBMW]

You wouldn't want to underdrive a water pump pulley on an e30 swap, since many swaps dont run traditional radiator fans. Could be a recipe for overheating disaster. Underdriving the PS pump and alternator is ok, since e30s weigh less (requiring less PS boost) and have fewer electronics (requiring less alternator power)

[tonytony]

I wouldnt' say you "dont" want to use it, it works just fine, i drove mine with a WP underdrive pulley without a fan, no issues, also if the crank is underdriven then everything is underdriven also. AS long as everything else is working then there should be no problems. I've just never seen this combo before, it's usually WP, PS, sometimes alt; but never crank and PS and no WP, that's all i'm saying, good luck with the sale

[dude8383]

Does this actually do anything?

[CorvallisBMW]

I wouldnt' say you "dont" want to use it, it works just fine, i drove mine with a WP underdrive pulley without a fan, no issues, also if the crank is underdriven then everything is underdriven also. AS long as everything else is working then there should be no problems. I've just never seen this combo before, it's usually WP, PS, sometimes alt; but never crank and PS and no WP, that's all i'm saying, good luck with the sale

Agreed, it is a wierd combo. But I got them in a parts trade, i didn't order them myself. We'll see if they sell like this. If not, i will seperate them.

Does this actually do anything?

Yes. It reduces the speed at which the accesories spin, thereby reducing the amount of hp the engine must devote to them. The hp that is no longer being used to drive the accesories gets sent to the wheels instead. It's not a huge boost, but it is a very common upgrade IIRC

[ethree]

What is the diameter of the crank pulley?

[vpilarrt]

Does this actually do anything?

Actually - yes, no, maybe.

An "underdrive" (meaning smaller for a drive pulley) crank pulley will slow down the speeds of all accessories being driven by that pulley; PS, water pump, alternator, AC, whatever. An "underdrive" (meaning larger for a driven pulley) PS pulley will slow down the speed of the PS pump. This could be a smaller PS pulley than stock so as to bring the speed of the PS back up to normal or if this is a larger PS pulley than stock the combination of the 2 pulleys will greatly reduce the speed of the PS - maybe too low (?).

[CorvallisBMW]

What is the diameter of the crank pulley?

I will measure it later today and let you know

[CorvallisBMW]

Bump, updates in first post with dimensions

[CorvallisBMW]

Bump

[ethree]

Are you willing to seperate these? I am only looking at the crank pulley, my p/s cannot be any more underdriven than it already is.

[CorvallisBMW]

Are you willing to seperate these? I am only looking at the crank pulley, my p/s cannot be any more underdriven than it already is.

PM'd

[CorvallisBMW]

Bump, Crank pulley sold. PS pulley is still available