underdrive pulleys

[fryedaddy]

do under drive pulleys amount to any hp.if so im running an alt and water pump only.do you change the crank pulley or the water pump pulley,or both.someone explain please

[TJ]

I cannot speak to the hp savings though I found out an underdrive pulley caused my wipers to move slow while sitting at stoplights with the headlights on.  Also, the coolant warmed up a little at stoplights on hot days.  Since I have a truck and not racing, I replaced the underdrive crank pulley with a larger pulley.  Now the coolant stays the same or cools slightly idling and the wipers maintain speed with the lights on while idling. 

If I remember correctly, my crank pulley and water pump pulley are now 1:1. 

[frnkeore]

I would change the crank pulley, first since it slows everything down and is most cost effective.

[fryedaddy]

I would change the crank pulley, first since it slows everything down and is most cost effective.

i was hoping to get by with just one pulley,but i wanted to make sure and get the right one.my crank pulley is 6.0 and the one i looked at was 5.4. im not worried about the wipers,i dont drive it in the rain anyway.

[Stangman]

I got the 5.4 on the water pump I think it helped with cooling. Maybe a 3 to 5 degrees.

[6667fan]

Every FE that I put a significantly smaller diameter wp pulley is on has resulted in cooler running temps by much more than five degrees. The desired ratio for achieving a decrease in running temps is 1.25/1 or higher. Decreasing the crank pulley diameter negates/ minimizes this effect. If the OP has any trouble keeping car’s engine from getting too hot, undersizing the crank pulley would likely make it worse.
Some back to back dyno tests would be in order to validate hp gains from under driving. How many ponies are expected to be found by under driving?

[66FAIRLANE]

Every FE that I put a significantly smaller diameter wp pulley is on has resulted in cooler running temps by much more than five degrees.

It doesn't take much. Someone gave me fancy looking aluminium water pump pulley so I put it on. It was only 3/8 bigger in dia but the car got hotter so took it off.

[fryedaddy]

well,it runs good and cool,and it seems to be working good.i should leave it alone i guess.but i like to get everything i can out of what i have

[StarlinerRon]

It's just math, the slower you turn the wp & alt the less power they will eat. City cars will be affected more than highway cruisers. You need to know how much cooling & voltage you will need to be safe.
Good luck,

Ron.

[Falcon67]

Personally, I wouldn't bother.  You're not going to save any noticeable power IMHO.  I never bothered even on the race car, think about the stock alternator buzzing along at about max 14,000 RPM on a pass