Originally Posted by fraser19
ok so i have hear alot about underdrive pulleys but i just dont know what they do, who makes them, what power gains i could expect, how they work and what engiens they will work on ect
i have a 2008 b4000 4x4 what would a or some underdrive pulleys do for me?
The purpose of an undrive pulley is to slow down the rotation of the motors front drive accessories. By slowing them down you reduce parasitic loss and "free up" horse power. You not producing any additional power, just using less on the accessories like power steering, alternator....
You can expect small power gains from pulleys, some people feel the motor "spool up" quicker. Personally I love my UDP's and wouldn't go without them. The one thing you need to watch is that your alternator is not turning to slow with the under-drive pulleys and your battery is discharging during idle. If you experience this, an overdrive pulley for the alternator will take care of that.
There are companies out there that make UDPs for the 4.0 Liter motor, but I'm not familiar with who.