underdrive pulleys with AA S/C?

xM3x · #1 (**permalink**) 03-04-2005, 10:36 AM

iam trying to put underdive pulleys on my M3 i have a AA s/c kit. not sure about the belt size, does anyone know or have any info? thanks.

Aaron

silforty · #2 (**permalink**) 03-04-2005, 11:30 AM

Im not too sure about BMW's but for some other cars, a lightweight pulley might be asking for problems in the near future. Cars like mine have a stock dampening on the pulley which has a good effect of reducing vibration on the pulley, if you switch to a aftermarket, it WONT have a dampener. I have not seen any lightweight aftermarket pulleys with the dampener. Plus the other down side is you would more then likly have to change your belt(s).

GOTUBCH · #3 (**permalink**) 03-05-2005, 09:27 PM

I believe he is asking about under driving the ALT, Power steering I have wondered the same just need to figure out how much difference inthe underdrive pulleys and add that to the supercharger belt. I have often looked at doing the same mod let me know how it goes.
Thanks,
Damien

xM3x · #4 (**permalink**) 03-06-2005, 08:29 PM

someone has got to know this! help! lol

Glucas21 · #5 (**permalink**) 03-06-2005, 10:25 PM

You will only need a belt that is one or two sizes smaller than what you have. Go to a local auto parts store take the belt off in the parking lot and walk into the store with it. Ask them to find belts that are a little smaller than what you have, and then see if they will let you try them on in the parking lot. If they won'tlet you, buy them and then try them on the car because you can always return them. you should be able to find the right size pretty fast.

xM3x · #6 (**permalink**) 03-07-2005, 04:22 AM

yea, thats what i thought but i just wanted to be sure. thanks

reavisM3 · #7 (**permalink**) 03-07-2005, 06:12 PM

Underdrive pullies are larger in diameter therefore you will need a belt that is longer. Buy two belts that are larger, take them home and see which ones fits best. Take the other back. I had to use one that was about 75mm longer. Check the last three numbers on the belt, that is the length in mm. I had to go from a 1555 belt to a 60630 belt. 555 and 630 being the length. I am running Turner Motorsport pullies, but different brand pullies may differ slightly.

GOTUBCH · #8 (**permalink**) 03-07-2005, 07:14 PM

OK if you have underdrive pulleys and your factory belt for the acc, Just add the difference in length to the super charger belt.....it is really quite simple I believe. Maybe I am wrong.If factory acc belt is 555 per say and Underdrive belt is 630. Then you would simply add 75 mm to your supercharger belt. The belt length is very important so you do not get slippage but if you know all the info just a matter of pluggin it in.

Glucas21 · #9 (**permalink**) 03-07-2005, 08:23 PM

Quote:

Originally Posted by reavisM3

Underdrive pullies are larger in diameter therefore you will need a belt that is longer. Buy two belts that are larger, take them home and see which ones fits best. Take the other back. I had to use one that was about 75mm longer. Check the last three numbers on the belt, that is the length in mm. I had to go from a 1555 belt to a 60630 belt. 555 and 630 being the length. I am running Turner Motorsport pullies, but different brand pullies may differ slightly.

There are two ways to underdrive the accesories, first by making the crank pully smaller, or buy making the rest of them bigger. So If he replaced the crank pully then a slightly smaller belt would be needed. But if he changed the rest of them, then a larger belt would be needed. I'm not sure which he did, so I can't say what size he needs.

reavisM3 · #10 (**permalink**) 03-08-2005, 04:33 AM

Yes, I know this. He did not specify but most people run accessory pullies so that they can run a lightweight flywheel later. Just going with the most common.

xM3x · #11 (**permalink**) 03-08-2005, 11:03 AM

Quote:

Originally Posted by reavisM3

Yes, I know this. He did not specify but most people run accessory pullies so that they can run a lightweight flywheel later. Just going with the most common.

sorry i did not say but yea i do want to run the LTW flywheel so no crank pully, i think iam going to fo with the UUC stuff. but thanks for all your help. i know what i have to do now.

Aaron