I see more and more people talking about having underdrive pulleys. First off what do they do and what are the advantages/disadvantages of installing one. I am running a stock 4.2 except for a cold air intake.

 

A set of under-drive pulleys turn your engine accessories (water pump, PS, alternator, etc) slower. This supplies less power to them and in turn frees engine power for moving the vehicle. How much and if you feel it is a subject of much debate.

Advantages: More power, better fuel economy.

Disadvantages: Depending on the amount of UD, your alternator might not charge effectively, your water pump wont flow enough and you will run hotter, your PS wont work as well, as will your AC.

I've had one on my 2000 3.8L mustang for years now, which has a very similar motor to your 4.2L F150. I'd say the power adds some pep back that I lost due to large wheels and tires. I believe this is the one I have http://www.vmptuning.com/store/index...d=87&parent=52.

The only down sides I've noticed is in the last year, now that the car is a decade old, the AC is still cold, but no longer frigid, and the PS gets a little heavy at idle, blip the throttle and it gets easy again. No charging or overheating issues. I should make it clear, the car did not develop these issues immediately, only after age and wear took away enough efficiency in the components to cause these minor issues. I think a PS flush and AC recharge would take care of it though.

 

Everyone I've talked to with a UD pulley mainly saw an increase in gas mileage.. .5-1mpg more.. and that's a honest .5 mpg more. Power will be minimal but it'll be there.

 

Just a quick note on BigIrish's post I believe BBK makes a set of UDP that claim to have no overheating/charging issues whatsoever after the swap. UDPs aren't something you will really notice, and are somewhat of a waste of money in my personal opinion. However in theory they do return that wasted power from the OEM parts on the engine. If you wanna blow some money on a few extra horses I say more power to ya man.

 

The issues you run into are dependent on the amount of underdrive. As long as you get a kit designed for street performance, around 10-25% UD, charging and cooling shouldn't be an issue.

If you want a good 30-50hp increase for a very short time, you could always do the drag racing trick of taking the belt off altogether. No AC, No PS, the car runs off of battery and you only have about 5 minutes of run time max before overheat, but you get a good hit of extra boogie.

A track only trick from the Mustang world is known as the shorty belt where you use a short as belt as possible that only drives the water pump for cooling.

 

off the shelf set, I wouldn't run them...

But i do plan on pretty much haveng some over driven and some under driven pullies on my truck. Basically buying all my pullies seperate, which gets pricey, but it's the best way to not get over heating problems, headlights dimming from not an adiquite charging system and too many asscesories (winch, kc's, system)

 

I think your idea of speeding up some acessories is a great idea. Like your alt so its putting out some more juice at idle and up. I think Putting ud pulleys on off road trucks is kind of going in the wrong direction. I wonder if anyone knows any stock interchangable parts to change pulley size.

 

Unless you run an electric fan! I plan on doing the electric fan, which I have read is more of a gain than UDP's anyways.

 

whats the best place too get underdrive pulleys for 5.4

 

Not true. No belt = no water pump = overheat. The only way to not overheat without a belt is to run electric fan and electric water pump.