Carl Fausett

Recommended for Competition Use Only

Application: Porsche® 928, 944, 968 models with 6-rib alternator pulleys.

Benefits - Lightweight and Larger: Like an aluminum flywheel, a lightweight alternator pulley reduces rotational inertia on the engine for faster revs and deceleration between shifts. Also, the larger pulley slows the alternator down, saving energy that can now be used instead to drive the car.

The stock alternator pulley is designed for stop-and-go traffic, low rpm's, and high loads caused by accessories, air conditioning, etc. In competition, we rarely idle and our electrical loads are much lower. An underdrive pulley saves HP and correctly moves the alternator into the competition RPM band.




Prices here:
http://www.928motorsports.com/parts/...ive_pulley.php

Randy V

Looks nice.

Because it is a larger diameter, the alternator will have fewer RPMs and thus less power output - right?

James Bailey

Very nice looking.....but with USPS flat rate small box shipping at $5.20 and they give you the boxes ????looks like a 100% mark-up on shipping ! I have always felt that "overhead" should be factored into the parts price but that is just my opinion. I object to car dealers charging a "documents fee" which is added to all the sales. Makes the quoted price a bit less real.....

Randy V

Funny, Jim.

Reminds me of ebay sellers - the small item is $9.95 plus $12.00 shipping!

James Bailey

Or the late night T V commercial......and there is more ! you get a second set FREE ! just pay separate shipping and handling. Like it is going to come in two boxes

GregBBRD

OK....Totally seriously now....nothing negative. Not hijacking the thread...not saying anything bad. Time out (on my part) regarding my issues with Carl.

I just don't understand this and need someone to explain this to me.

The alternator is a self-regulating piece...that's a given. It has a regulator that has a "pre-set" voltage. Once the voltage, in the vehicle, drops below that pre-set level, the alternator is called upon to make as much current as needed to bring the system back to the pre-set voltage. Correct?

The "power" required to turn the alternator is determined by how much current the alternator is being called upon to deliver. The higher the amperage needed to keep the system at the "pre-set" voltage, the harder the alternator is to turn. Correct?

How does the pulley diameter reduce the amount of power required to turn the alternator?

Seriously now....

If the alternator requires one horsepower to make it turn to generate 40 amps of power....how does that change when the diameter of the pulley is changed? Seems like it would still require one horsepower to drive the alternator....

Explain this to me.....I can be very slow.

Imo000

If the pulley is large enough, long idling can drain the battery to a point that when the engine is shut off, it will not have neough power to crank it over. If you have a light weight battery on a race car, this can happen quick.

blown 87

I wish they made a pulley that was smaller, most will not charge at idle, from what I have seen.

SeanR

I thought shipping was a profit line for some of these guys.

blown 87

Guys, every person that make a living selling parts for cars, or working on cars has to make profit on everything, or at least try to, for the most part, paying extra for shipping just covers what it really cost to ship things.

Be it Carl or who ever.

It has no bearing on the part we are talking about here IMHO.

robot808

Agreed. The cost of shipping is not what USPS charges...

BC

I'm going to have to make a couple pulleys that are offset a bit forward or back. I wonder if I could "borrow" that file.

genikz

This makes perfect sense for competition. My track car idles until warm, then it's 4k+ rpm for the entire session.

My 15lb motorcycle battery is just there to start the car. I pull the kill switch when the cooling fans turn off, and keep a battery tender on it when garaged.

Competition vehicles have next to nothing in common with street vehicles.

docmirror

The answer to this is really complex, and deals with dyne fields, and torque loads of angular momentum as well as the cumulative alt RPM vs engine RPM. I'm not going to bother with it all, but please trust an EE with about 25 years of auto experience that it will work as advertised for track cars, or other street cars that spend very little time idling, and most if it's time at highway speeds.

The mission design is correct, and looks to be appropriately sized for the activity planned. For the track car, buy it, install it, and it'll work just fine.

GregBBRD

Carl says it is for competition vehicles only. That's not my question.

I don't understand the benefit of bigger pulleys on something that takes a "fixed" amount of power to turn. I grasp the benefit of a different size power steering pulley...or a different size water pump drive...or a different A/C drive pulley.

I just don't get the alternator pulley.

Like I said, if it takes one horsepower to turn with a small pulley, it seems like it would take one horsepower to turn a pulley the size of a trash can lid.

What is the benefit?

Someone explain?