What are some of (if any) the advantages or disadvantages between an aluminum pulley at 8 ounces and a steel pulley at 15.5 ounces? I've read some things about the lower inertial mass, but how significant is it? Is there a reliability issue? Or is it something you'd even notice during day-to-day driving?

Thanks.

 

Is this for a crank pulley or a supercharger pulley?

My thinking is the difference between a steel & aluminum flywheel is huge. The difference between a steel & aluminum crank pulley wouldn't be to much. It's a very small diameter & the difference in rotational mass wouldn't gain you much. If it is for a supercharger pulley then the difference would be minuscule.

Lots of folks believe in those light weight pulleys. Me no so much.

 

If it ain't titanium, it ain't s---!

http://1346843.estore.networksolutio...tail.bok?no=99

 

an leave out TITANIUM ?

UBER explains all.

 

^ 800 BUX!?

 

Thanks! Yeah, it's for the supercharger pulley. I have a 15.5 ounce 2-piece design thats about to go in. While I just can't see 8 ounces making that big of a difference, given that these thing spin at a really high rate I want to be sure...

 

$800!?! But then again, it is weapons grade titanium

 

And you have no idea the personal risk to life and limb that the artist had to go through to secure that block of weapons grade titanium from a fabled industrial military complex hidden deep in the desert... it's a bargain when you consider that.

 

You won't be able to tell the difference between 8 ounces of inertial mass on a supercharger pulley, trust me .

 

I figured as much... marketing! Thanks for the opinions.

 

It's such a small radius that you probably couldn't measure the difference in engine output.

 

Yup. A rotating mass in itself isn't a bad thing, it's when you move the weight outside of the point of rotation that it starts taking more and more power to start said rotation .

 

And for the SC pulley you have to consider thermal expansion. Aluminum expands at a different rate than steel. With an alum. pulley you can have slipping issues until all working metal parts have reached operating temperature. As well aluminum under stress has a property know as cold flow. The metal will move and change under stress. Which put simply allows the bolts clamping it in place to loosen over time. Causing massive slipping, ie: boost loss and coolant system temperatures to rise. Now as long as the alum. pulley has a steel hub it bolts to you'd be alright. But, I wouldn't waste my time with a full alum. pulley.

 

All of the theoretical considerations you cite are true, however, most of the aftermarket SC pulleys in use on MINIs are aluminum. They work fine, and I've never seen a post complaining that one has come loose - it's just not an issue, in practice.

If it concerns you, an alum. pulley with 6 bolts is probably better than one with only 4.