I'm looking at getting a set of underdrive pulleys for my truck it's a 5.0 mostly stock except for a Cold Air Intake. I just wanted to know if these are worth getting? Do they give a noticeable MPG and Power increase?

 

no...

and if you sit idle alot they will actually drain the battery as the alternator doesnt spin fast enough to keep up...

 

yes....

They work perfectly fine, no issues at all.

 

i've got them on my truck and i love them. Yes when you are sitting at a stop light you can watch your headlights dim and your charge gauge drop but i've never had a problem with them draining the battery. i go muddin at night all the time, and i've got a sub with a 1000w amp and we'll sit and idle and b/s for an hour or more with the music blairing and headlights on and i've never had a dead battery my trucks still got the stock alternator too and the pulleys have been on for over 10,000 miles so i wouldn't believe the premature wear on the alternator. Of course every truck is different... i never keep track of my gas mileage on the count of my tank leaks if i put it over half and having 38's and stock gears i'm probably not gonna get much improvement there... but i would recommend them you really can feel a difference in the power.