Are there any real benefits to installing under drive pullies. What happens when you lower the rpm to the power steering pump,alt, water pump,etc. But if you don't change the crank pullie the rpm will increase on alt, etc. Do you really want to lower the rpm on the water pump ? ( decreased flow and pressure )
What am I not understanding.
Thanks, Ron

 

I've played with them and don't feel the benefits are worth the cost. All the rotating components such as alternator, water pump and power steering pump are designed to run at a specific speed in relation the the engine speed. Slowing them down just adds other problems especially for a low rpm, street driven vehicle.

I run 3 belt driven devices on my race engine. An alternator, a vacuum pump and a fuel pump. I'm not sure what the vacuum pump ratio is but the fuel pump is calibrated and needs to spin at 1/2 the engine rpm and the alternator works best at 3 times the engine rpm. I could slow the alternator down a bit as I use a CS style and it charges very well at lower rpms. My water pump is electric and runs at a constant speed but then my engine never runs for long periods of time to get hot enough.

 

Thanks, I really could not see any benefit as you stated without causing other issues. The only way to be safe would be to drop all size's ( crank, alt,etc ) at a 1 to 1 ratio and what good is that.

 

Not worth it.
I am running one, PS works ok...I used a HV water pump to compensate its on the edge. Seems passable as I idle the car at 11-1200 due to a large cam
The alt is the weak spot it does not charge til the rpms get up there.
So either find a small alt pulley or large crank pulley. Whats the use.

Think my alt is 1.3:1 not nearly enough has to be at least 2:1
Pass on that mod if you can.

 

The set I put on also changed the alternator pulley so that charging wouldnt be an issue. There was no noticeable difference in performance. No cooling issues. I will probably be swapping back sometime in the future since I believe it will help with my A/C compressor at idle. Right now it is alittle too slow.

 

I run the old SLP crank underdrive on my car. No A/C in my car. I also run a overdrive (super small) alt pully.
my car idles at 550rpm and is a solid roller with a duration of 258ish @050.
I do have a lil dimiming issue with the lights and things at night but nuthing crazy.
Id say its on the edge but I can deal with it..

 

If your cruise RPM is above 2000 at 65 MPH, then do the pulleys. If not, don't.

 

Hot Rod magazine did a build on a car of 4 different motors. On each one, after getting the HP/TQ, they added underdrive pullys from March to see if they were worth it. They got less than 1Hp gain over 6000 rpms on each motor. So i'd say no, it's not worth it.