Under drive pulleys are pulleys that are different size than factory .
Under drive pulleys will make the acc`s ( P/S , A/c , Alt and water pump ) on your enigine turn slower . Thus makeing less work for you enigine and freeing up alittle extra HP . A good example of this would be ... with factory pulleys your acc would turn 4 times . But with a 25% UD crank pulley they would only turn 3 times ( if I understand right )
Some say that their lights will dim at a stop light or have chargeing troubles . I`d think alot would depend on how many highway / city miles you drive . If your sitting in traffic or lights for extended periods of time it might drain your battery some . I have not read anything about over heating .
Others say that B/C you are turning your acc`s slower that it extends the life of them and your enigine too being that it works less . I would think being that your enigine is working less you might also get a few extra miles on a tank of gas .
If you go back through the old post their are some excellent threads on this . Or maybe even try FAQ . Maybe you could also post this on the tech board
__________________ 1998 3.8 mustang , orange , cobra hood , wings west body kit , clear diamond cut head lights - side lights , GT fog lights , H pipe - new GT exhaust , CAI , UDP
And more to come as I get the $$$$$ LOL
2001 3.8 mustang wrecked ...... winter project car
03 cobra hood
grille delete kit w/ pony | 
