timeformiller44

i know with F/I you dont want to use underdrive pullies...but with nitrous would it be a good thing to have them?? bad thing?? no diffrence??

sstang

You only don't want to use underdrive pullies on supercharged applications. This is because the supercharger is belt driven as well, so I guess itwould makethe chargerwork harder and lose efficiency. For turbo and nitrous, underdrives are okay.

timeformiller44

do you mean like ok...they dont do much...lose power....or help somewhat

timeformiller44

bump

2000GT4.6

Underdrive pulleys increase WHP because you don't need as much power to spin the accessories on the front of the engine (a/c, power steering etc) because they are all spinning at a lower speed.

A blower is belt driven, so you cannot run an underdrive set. u/d pulleys mainly decrease the speed by changing the crank pulley size. If you were to do this with a blower, it would slow down the pulley on the blower, and the blower would not make as much boost. You could pulley down the blower, but a smaller pulley size on the blower will increase the chances that you will have belt slip on it (which will tear up belts and loose boost). Also, it would be very hard to figure out what pulley you acutally need for xx boost, as nobody rates their pulleys based on a underdrive crank setup.

You can run u/d pulleys on a nitrous car no problem. Nitrous has nothing to do with the belt, so it will work just as well on a n20 car as it will on a n/a car.

MU71L4710N

i thought underdrive pulleys kept the same belt size though? they decrease the waterpump and alt and increase the crankshaft size dont they? so how would that hurt the blower...the belt still travels the same distance?

or is i wrong?

2000GT4.6

The belt travels the same distance at a different speed. Thats the problem, the speed of the belt changes, and that throws off your boost level (as it changes pulley RPM on the blower).

SlvrOhTwoGeeTee

what kind of gain would you see by adding UDPs and removing the AC? Does removing the AC pump even make a difference if it's not on? I am thinking because the clutch on it is disengaged when it's not on than it wouldn't have any noticable parasitic loss. Anybody have any experience on it?

MrChubs1

There's minimal loss to a/c if it's not on. Almost zero, just as you'd think.

I assume you could underdrive the water pump and alternator without changing the crank pulley in a supercharged application. That would probably be the way to go.