burnout083

i really don't know anything about under drive pullies. i get the concept. some how its works less on the accessories and more on the motor. but why and how? what pullies need to be replaced? can you replace all of them? who makes good pullies? someone please help my ignorant ***.

CBSTANG

The two pulleys that are replaced are the Crankshaft pulley and the water pump pulley, when you buy new pulleys the size of the pulleys change to be able to reducethe parasitic drag. The Crankshaft pulley is made smaller and the water pump is made larger, and Im not sure on how the physics of it work exactly but someone elsewill probably be able to explainit to you better. There are some kits like motoblue I believe that come with an idler pulley, but have heard are even heavier than the stock one which in turn would lessen the performance a bit. I have the steeda pulleys, I like them, and mine seemwell made. They were a bit of work to install though, especially if your like me and don’t know loads about part removing and installing. Once i installed mine I was able to feel a difference through the pedal though and my mpg increased a bit too.

Getaway

You're right, they reduce the parasitic drag. The small crank pulley reduces power to all accessories since it is the crank pulley that drives all accessories. The larger water pump pulley compensates for the smaller crank pulley because you don't want to reduce the power to the water pump because a cool engine is an efficient engine. Some people get electric water pumps to go one step further.

BTW: If you plan on supercharging down the road, you will put the stock pulleys back on because the supercharger is essentially an accessory, and you definitely don't want that one underdiven!

burnout083

now i have seen udp marked as 10percent and 25 percent. what does this mean?

dirtydeedsinc

10% or 25% underdrive. That's the percentage it will underdrive everything or reduce the speed of your accessories. Higher percentage, lower speed.

05SDI

Don't take this post wrong but;
There are down sides to UDP

If you thinking of adding things that draw morepowerfrom your battery(lights, amps etc) you may NOT wan to go for the 25% UDP. Yes it should free up more HP but in return it slows the speed of all your acc. Your car may not be charging the battery at an idle. There are sharper peeps than me on this that may chime in as I don't have any experience with our Mustangs but I have done it on both SBC and Hemi.

burnout083

i've heard that. the only thing i'm adding is the roush front bumper so just the 2 more fog lights. but how dramatically are the 25% pullies gonna affect the accessories? i mean is the radio gonna go out on take off or something?

BillyBobJoe

I've got the SLPs at 25%. I haven't had any problems yet. I drive with my fogs on and the Shaker 500 going. Not loud but on. The needle on the volt meter has yet to move from the charging side of the gauge, even at idle. I've had no problems. The install was nice and easy too.