Hey guys,

I was wondering what your thoughts are on underdrive pullys. Most companies that sell them advertise a 10-15hp gain but I was curious if anyone actually has any experience with them or any actual before/after dyno results to prove or disprove what they advertise. The reason I ask is I'm looking at a set from BBK, the steel ones are only $80ish and the aluminum are $160ish and wonder if they are actually worth spending money on. Thanks!

 

First off, there are 2 different types of underdrive pulleys.

1. Changes the alternator pulley to where the alternator is turning at or near the stock revolutions. This style will keep your charging system working as it does now.

2. Will decrease the charging system capability. This kit frees up more hp then kit #1. The alternator under load definately puts a draw on the system.

I installed the kit like #1. I didnt want to worry about any charging problems. I had to install a new smaller diameter crank pulley and a smaller diameter alternator pulley. My car charges just fine. However, I could not notice any improvement from the butt dyno.
Personally, I think underdrive pulleys should be at the bottom of the list in mods. When you have all the other bolt ons, and you want to do just one more thing, then do it if you want.

There are other ways to get better performance for the dollar.

 

I've used aluminum UD pullies on 7 different vehicles and they have always worked exceptionally well in each case.

Aluminum cuts the rotating mass if you get the right ones. I grab them at swap meets where you can instantly tell how heavy they are.

Many times a stock stamped steel water-pump pulley is much lighter than the aluminum version, and if you look you can often find larger diameters than what is offered by UD pulley makers.

Most pulley sets available only show 10 - 15 hp improvement.

If you go with a 4" crank pulley, a 7.5" WP pulley, and delete the power steering, A/C, and air pump, you can see around 25 hp over stock.
A smaller alternator pulley would be required for street use.

Since this is an opinion type question, I will say that I think they are worth it.

 

I put one on my V6 last spring, I saw a 1-2 mpg increse after it and did notice the difference in power. I drove it around to get the feeling of the car fresh in my mind, did the swap, then drove the car the same places and could tell the difference.

On the down side, on real hot days my car was getting hotter than I'd like it, especially if I was at a stop light, new thermostat should fix that. Charging was erratic some days, some days it would charge normally all the time, others the volts would drop at idle.

They're cheap and easy to install, I say worth it.

 

i just picked up my bbk alum pulleys the other day. they look to be nice pieces. i wanted to slow my water pump down for the most part cause i blew a frost plug last fall at around 6000rpms. but they are nice and light weight and like i said appear to be nice pieces. ill let you know wat i think after i get them installed

 

I have BBK underdrive pulleys and they appear to help out a bit. I never got to drag strip test them to see if it made a difference but they look good and I know its one less mod on the list

 

I would love to see an actual Dyno result of before/after simply because while I know "I could tell a difference" means something, its just so hard to subjectively quantify.

 

keep in mind that you will certainly not notice any improvement if you have a mechanical fan. the fan is way more drag than any pully or accessory. go electric if you dont already have it.

 

I have a set of alum BBKs in my garage right now and they look very nice! I am going to wait to install them with a new water-pump, hoses and AIR pulley later down the road...

 

i plan on installing them today . wont really be able to test them thogh since we got two inchess last night. i hate the midwest

 

well the pulleys are on. only 2 things i really noticed.

1. the waterpump pulleys is exactly the same size. other than being alum and lighter its really only pretty and thats it.

2. the alt pulley is just a tad to thick for my liking. everything lines up but there isnt enough room to reinstall the lock washer and the stud doesnt purtrude all the way through the retaining nut.

other than that they look alright.

 

Some pulley and underdrive pulley comparison pics:

http://s702.photobucket.com/albums/w...adis3/Pulleys/

 

I changed to march underdrive pulley's and an electric fan and my 1/4 times went down about .2 to .25 seconds. Charges just fine too. I did it because my car was throwing belts at high rpm so I needed a serpentine belt setup.