I installed a 4.0L ASP Underdrive crank pulley
and then data logged the power results during the holidays. And now I've put about 5k miles on it so far.
Here a few quick notes..
Right at 5050rpms I gained 12hp
Basicly the whole torque curve moved up & I gained some TQ up top.
You can definately feel the power increase. Everywhere & no matter what throttle or speed your traveling at.
Gas milage is up a little too. Don't know exactly how much. But it's up. (avg-ing 18s now)
I've had ZERO issue with cooling or electrical power. It's not really been warm enough to run the AC yet.
I've put underdrives on 3 different cars now. And IMO it's a very solid bang for the buck. This ranger seems to have had the best results IMO too.
Belt size. I marked all the locations on my tensioner. (no load, lock, stock belt) And when I went to get a belt all the local store had was a 85" gatorback. It's been on there since and works good. It's operating at about 1" less of rotation than the stock belt even when it's got some heat in it. I'm keeping an eye on it because I am curious how much it'll grow in the summer heat.