I've been reading over the numerous posts about UD pullies and I guess I would like to get some clarification/confirmation of my understanding about the details. Can you all check me on these please:

1. crank pulley slows serpentine system down. other pullies then needed to "overdrive" certain accessories - water pump, alternator, leaving ps pump and AC pump to be underdriven?

2. 2 vs 3 pulley kits - 2 pullies = crank + waterpump, not alternator. Therefore, the idle needs to be ramped up a little to help alternator to put out current at idle. 3 pulley kit = crank+waterpump+alternator. No idle adjustment as the alternator pulley compensates for underdrive crank.

3. crank pulley either needs to be heavy to act as a harmonic ballancer, or, it must be able to have the balancer bolt on to provide dampening. Which is best - solid pulley or bolt-on?

4. No negative posts that I saw. Mostly either did not see any difference or slight difference off the line.

5. Some minor gain in mpg (1-2?)

6. Aluminum vs. steel - pros and cons?

did I miss anything?

I'm just trying to get my facts straight about how these kits work. There doesn't seem to be much in the way of documentation on the websites other than some basic installation. I've seen some kits "rated" by % of underdrive. Is there a particular optimum reduction, 25%, 50%?

My interest is just to help the mpgs a little. I see the Mac pullies for $140.

Anyone have any recommendations? This is for an 03 Ex, 4.6l, Troyer tunes with Xcal, AF1+FAL efans+Royal Purple.

Thanks.

 

http://www.marchperf.com/underdrive2.html

good article...may help in your thinking

also you can talk to troyer and see what his thoughts are on them...pros cons...i trust him

 

i never trust anyone whos trying to sell u a product. its like trusting a car salesmen to know something about the truck they are selling u..

 

1. All go underdrive.
2. yes.
3. You need the OEM balancer in place no matter what you do.
4. May or may not see a difference.
5. May see a difference depending on a fan/clutch or electric fan use.
6. Makes little difference. There not large enough in diameter to make any difference.
understand that reducing accss speeds then speeding up some functions takes defeats any benifits you may gain.
Unless the Alternator spins fast enough at idle and low speeds, the headlites and A/C may not operate as intended.
Your electric fan use may also be affected at or near idl = cooling problems along with slower water pump speeds.
IMO it to much money for the little gain and other hassle you get with it.
Measure you stock crank pully and the alternator pulley and figure the ratio stepup. Try to keep this ratio for power needs.
Do the same for the rest of the system before you make any changes, then you will know what suffers from the new ratios and what to do about it.

Example: crank pulley = 6" , alternator = 3". The ratio is 6 divided by 3 = 2.
This means the alternator speed is 2 times the crank speed.
Said another way if the crank speed is 600 rpm idle, the alternator is at 1200 rpm.
Use this method as a reference to know what you are doing.

 

Thanks Bluegrass! I kept having to scroll up to my original post to re-read my questions so I could figure out what your answers were answering

I think a few kits have as the new crank pulley a balancer built in (ASP, Summit Racing brand). The aluminum pulleys apparantly need to bolt the old crank on for dampening.

The ratio calc is very helpfull. I had read that somewhere and forgot to bookmark it. Most of the kits out there just tell you "it fits". Little or no spec other than perhaps that it is 25% UD. No diameters, no count of pulley grooves (my Ex looks like it has a 6 rib belt.)

I want to know those details. I hate just "trusting" without knowing for myself.

Any other thoughts or recommendations are appreciated.

 

yes ive said before under drive pulleys show no rwhp gain!