Hi I just got a set of underdrive pullies for christmas and I was wondering if anyone knows offhand what size belt I need. They are the Ford Racing brand pullies.

 

Ford Racing #M-8509-A50 Serpentine Belt Horsepower Pulley Kit?
It uses the stock belt. The smaller drive pulley combined with the larger driven pullies add up to the same overall belt length

 

tried it today, stock belt is too long

 

What is the part number of the kit?

Adrianspeeder

 

At the risk of pointing out the obvious, are you sure that you've routed the belt correctly?

 

yes i routed it right but i noticed while putting it back on after i re-installed the normal pullies that if i go from the crank to the waterpump to the airpump: instead of crank, waterpump, powersteering: it's a little shorter and seems to work fine. As a matter of fact i'm going to go try that right now.

 

Won't that require reversing the sense of the wrap on the water pump???
If it does, I can guarantee you that it will not work.

 

crap, i didn't even think of that, but it fit lol, i'd better go put it back though. i noticed a huge increase in power in my spin around the block though

 

The problem is that belts only come in fairly substantial increments. The next size shorter is likely to be too short. There's also the problem that the typical Counter Dummy at the big box parts stores wouldn't even understand the concept unless you can tell him what make, model and year the belt you need fits; they cannot deal with "the next shorter belt." If you have an old-style parts store where they have paper catalogues instead of being controlled by the idiot computer go there and find out how much shorter the next smaller belt really is. That may be your solution but I doubt it.

This is really perplexing since the FRPP catalogue specifically states that the conversion uses the stock belt and has done so since at least the 1996 SVO catalogue.

Are you sure you currently have the correct belt?

 

Well I went to Napa and brought my old belt along. The stock belt was 102.5 which my old one was too. This is also what it said on the troyer website. In the troyer kit it states that you need a 100 inch belt with the u/d pulley kit, so I got a 100 inch belt. The guy I delt with at Napa actually knew what he was doing, not like the morons at Advance auto parts. Anyway the belt worked fine and I never dreamed I would get the power increase I did.

 

The truck applications do in fact need a shorter belt. I have the Ford Racing #M-8509-A50 kit, three piece, and had to get a shorter belt. It's possible that somehow routing differences in the truck and Mustang let the stock belt work on the 'Stang, but I doubt it unless the tensioner has a lot more travel.

I didn't have any trouble finding the right belt, as you can usually get them in loads of different lengths.

I kept the packaging stuff so I wouldn't forget the size, but Troyer seems to have answered the question before I went and found it.

 

anyone know off hand what size you would need for a set of underdrive pullys and no smog pump??? lol

 

crap, wish i would have thought of that

 

Is there a negative side affect to the underdrive pulleys? I was really close to ordering a set, but I didn't pull the trigger, because I was concerned that I might adversely affect accessory performance - especially alternator. Do you notice any issues?

 

Only issue is that at idle, the lights are a little dimmer then when you give it a little gas they go back full. Its a small sacrifice for the power I got out of them.