Just measured mine.

Stock water pump: ~5 in
New pulley: ~7 in

So that's about a 28% increase.

If I remember correctly, the instructions that came with my pulleys said that to "maximize gains, install the water pump and alternator pulleys." Also said that installing them would let you keep your stock belt length.

So I think what it is, is that whatever percentage your crank pulley slows down (in my case, it's a 25% underdrive), the water pump pulley has to increase by that much to keep the belt the stock length.

 

what kit Doyou have, and how do you like it?

 

The one from Summit Racing for the 4.6 engine, with the long style water pump pulley (even though on the site it said I would need the short style kit.) Then again, this is for an 03 Expy, so it might be different/same for your year.

So far, I like it. Acceleration seems a bit more jumpy off the line. Don't have numbers yet on gas millage.

 

I can't use these because of my blower, but in previous experience with them on a modified 5.0 they were a nightmare. I had a 3 piece kit and had serious cooling and charing problems. I ended up dumping the alt and wp pullies for stock and kept the crank one and it solved the majority of my issues. Whie the theory is sound, the actual results seem to vary by truck and its acceptance to such mods. I personally don't like them or the idea of using more than just the crank, buy hey, to each his own. Start adding stuff like multimedia or stereo componentry and you'll problably have electrical issues, low charge and what not unless you upgrade your alt.

 

My stereo worried me a bit and the idea of in the future going with electric fans. I have a 235 amp alternator that should take care of that problem.

 

and they are great. Just to clarify- 3 pulley set, the crank is smaller than stock, the wp and alt are both larger which results in both the wp and alt being driven even more slowly than if you just used the crank by itself.

I did raise the idle rpm from 600 to 700 to help a little with water circulation. Electric supply was a little low (I also have efans), but not a problem. I notice my fans come on more often now due to slower heat transfer to the radiator.

I noticed an imediate gain in acceleration across the board, and picked up anywhere from 1.5 to 2 mpgs (mostly highway). Can' wait to try it on better summer gas. I usually lose about 2 mpg's during the winter.

This is one of the better mods along with the efans. I don't know why Ford doesn't put them in there in the first place, along with a much better tune on the computer (I have the Troyer tunes on the Xcal2).

Get the summit pulleys - quality made and alot cheeper at $159.00 than the competition.

check your water pump length as I show in my previous writeup:

https://www.f150online.com/forums/sh...mit+UD+install

you may need the kit that has the long style water pump pulley. The bell of the pulley is deeper by about 1" so the track of the belt on the other pulleys lines up with the water pump.

Great mod. Do it and enjoy the benefits