Originally Posted by serialk11r (Post 130735)

What I was getting at was that the overall moment of inertia of the engine comes from the pulleys, crank, and flywheel together. If the flywheel mass has a lower limit due to driveability, then there's not much of a point in switching pulleys because why subtract rotational inertia from 2 places (flywheel and pulley) when you can just subtract it from 1 (flywheel). The mass removed from the flywheel will have a much larger effect, and if you can just replace the flywheel to get the desired effect, there's no need to shave mass from the pulleys when you can just shave a little off the flywheel (I think machining flywheels a little is safe practice right?)

Originally Posted by WingsofWar (Post 130730)

Yeah it does depend on the weight, for many cars there are several versions of lightweight flywheels with different weights. A full race lightened flywheel thats nearly 50-60% lighter than factory is completely unforgivable on the street.

lightweight pullies arnt useless.. you really have to look at the application. Some crank pullies for many cars are stupid heavy and can use some lightening.

Originally Posted by old greg (Post 130777)

For a street car, yeah, there's no point in having both. But that doesn't make a lightweight pulley a waste of money. It is a pretty inexpensive and straightforward mod, and the stock pulley is not a harmonic damper so there's no reliability issues to worry about. For someone looking for a small change for not a lot of hassle, it's not a bad idea.

If you are super concerned with weight reduction though, a lightweight pulley with a not-quite-as-light-as-it-could-be flywheel will save a couple of pounds versus just a lightened flywheel.

Originally Posted by mines13 (Post 130783)

Flawed logic. The mass and diameter of an OEM pulley is calculated to counter the negative harmonic effects on the rotating assembly a higher engine speeds. This is not a matter of a "stupid heavy and can use some lightening" It is what the manufacture determined was necessary to counter these negative and potentially damaging effects for the particular engine.

Originally Posted by Subaru

Thank you for your patience as I checked with our Technical Services Department regarding your message below. They advised that the crank pulley is a pulley and nothing else. It is not used as a harmonic damper/balancer. Thanks for the opportunity to be of assistance. If you need any future assistance, please feel free to contact us again."

Best wishes, John J. Mergen

Customer Service Department Subaru of America, Inc.

Originally Posted by 7thgear (Post 130794)

if this is true, why wouldn't subaru manufacture the lightest pulleys possible at factory.

Originally Posted by mines13 (Post 130783)

Flawed logic. The mass and diameter of an OEM pulley is calculated to counter the negative harmonic effects on the rotating assembly a higher engine speeds. This is not a matter of a "stupid heavy and can use some lightening" It is what the manufacture determined was necessary to counter these negative and potentially damaging effects for the particular engine.

Originally Posted by old greg (Post 130789)

This is not true for the Subaru H4. The crankshaft is so short (ie: Stiff) that it's torsional natural frequency is well above anything it sees in operation.

Originally Posted by 7thgear (Post 130794)

two questions in light of the above

1. if this is true, why wouldn't subaru manufacture the lightest pulleys possible at factory.


2. in light of what mines13 said

in that regard, the pulley then functions as a unit together with the flywheel, so then by that logic we shouldn't be changing the flywheel either since its mass will have an effect on the overall balance of the system.

Originally Posted by mines13 (Post 130783)

Flawed logic. The mass and diameter of an OEM pulley is calculated to counter the negative harmonic effects on the rotating assembly a higher engine speeds. This is not a matter of a "stupid heavy and can use some lightening" It is what the manufacture determined was necessary to counter these negative and potentially damaging effects for the particular engine.

Originally Posted by WingsofWar (Post 130832)

:) see its not flawed logic. I understand where your getting at. But like i said..it depends on the application.

some pullies for some cars are really, stupid heavy.

Originally Posted by mines13 (Post 130847)

I'm not familiar with that unit of measure. ;)

Originally Posted by old greg (Post 130851)

It's the Metric equivalent of "Heavy as Shit". :D

Originally Posted by mines13 (Post 130847)

I'm not familiar with that unit of measure. ;) We won't bother covering the fact that no matter what, a crankshaft does flex to some degree. I've seen some pretty hammered road race engine bearings... I would never consider running anything less then an OEM pulley dampened or otherwise. Unless I was replacing a non balanced pulley with something that counters harmonic effect. Then again, I'm pretty anal about my stuff and would rather have and not need then to need and not have. I run an ATI on my Integra actually, and they have saved plenty of B and K race cars...