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Discussion Starter #1
uh, sure

anyone installed it yet? Im considering doing it to complement the lightweight crank pulley. BTW, I also saw a Cusco that weighed 7.7 lbs (but know nothing else about that part yet). Anyone?

Also, for those with the crank pulleys installed: when I told a tech at shop about this, he discouraged me saying that doing both a CP and a Flywheel mod together was a bad idea and would stress the engine too much - and he noted the lack of the harmonic balancer (the old debate on the thread pertaining to CP's). he said to do one or the other. Im wondering if this is just about the same old sh!t in the previous thread which was dispelled, or is there in fact a compounded effect from the two mods that will make it too hard on the car?

Otherwise, Id like having even less rotating mass and quicker response.
 
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Personally, I wouldn't want to go under about 14 pounds on a flywheel.

Light flywheels have a lot of drawbacks, and when you use them in addition to a light pulley, you will make the ride of your car a lot less comfortable. Now, whether or not, that matters to you is personal preference. But for me, ride comfort is important (one of the strikes against the evo when i was making my purchase decision).

Also, you may experience a much rougher idle, with erratic rpm jumps, this is common as well.

Finally, I would be very wary saying the pulley was 'dispelled'. It is a fact that engine life is reduced, whether or not people want to admit it, :). When you take out the heavier pulley and the heavier flywheel, that energy is displaced and it has to go somewhere, meaning other parts will be taking the stress. It may not kill your motor overnight, but it will effect it's long term reliability.

But again, that only matters depending on your personal comfort level. Some people won't care and for others that would be a big deal.
 

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There isn't any energy going into the flywheel or pulley. There's energy used to spin them. If they are lighter, it will take less energy to spin them so it will theoretically get to the wheels since they are not being used to absorb forces (like a balancer would be). Now, this is a trivial amount so you won't actually see a difference in whp though. Look at dynoing cars with lighter components like wheels/driveshafts. They will increase in hp because there is less rotating mass. I've seen it happen with RWD cars multiple times.

The drivability issues will be there, though. The revs will drop a bit more between shifts and whatnot. You're tranny might make more noise too. Other than that there should be no damaging effects (*if* the part is properly built and balanced).
 

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Re: Body kit !

on my old honda that i raced and drove on the street, i had both lt. wt. cp that was underdriven and 11lb flywheel. the hardest thing to get used to was the very rapid rpm drop between gears. next was getting used to starting off on a hill with less torque than it had. no ill effects were noticed in regaurds to engine wear, the car is still running with over 230,000 miles. i know the honda and suby have different engine configs but, don't think it would change the outcome over time.

ted
 

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Every power stroke of a piston will send a shock to the crank. The stock pulley has balancing and shock resistant components in it to dissipate some of the energy. That's why if you go to a bare piece of metal for a pulley it will reduce the life of your engine.

As for the flywheel, there's still alot of mass even on a lightweight flywheel, so it doesn't affect your engine life as much. What it does affect is how much rotational energy it can store. And no, you don't lose torque, what you lose is the ability to store that energy for when you need it, such as starting up on a hill. That's why a light weight flywheel affects drivability. It's also why you see race cars spin out as they leave the pits. If they don't spin out, they'll stall the engine because all of their components are so lightweight.
 

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Discussion Starter #6
2004 SWRT is set to go!

Just a FYI: i found out today (finally) that the stock flywheel is about 20 lbs and the "lightweight flywheel" is about 16 lbs - not much considering that the part goes for almost 600$ and near $1000 with labor :eek: . At this point, I dont see myself doing this mod until I replace my clutch to alleviate the cost.
 

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The stock STi pulley has no harmonic dampening ability. SOA verified this. Swapping a pulley that acts as a harmonic dampener would lessen the life of an engine, but not this one.
 

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The stock STi pulley has no harmonic dampening ability. SOA verified this. Swapping a pulley that acts as a harmonic dampener would lessen the life of an engine, but not this one.
 

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Our STi is already a 'low inertia' engine - hollow valves, hollow cam, relatively low mass flywheel, etc. As is it has a rough idle and spools up fast (compared to my old Integra). Yes the extreme is no flywheel like on F1...personally I'll leave the rotating mass as is considering cost and it still is my daily driver (winter too!)
 

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It doesn't make sense to put torsional damping functionality into a pulley, so the SOA ref above seems logical.

With all due respect, nobody could ever convince me that removing/reducing torsional damping (aka harmonic balancer/dampner) is risk-free. It may work in some instances, but just because it worked on a Honda is no garantee it won't cause your Subie to self-destruct - it's a crap-shoot unless you know there are no "system" torsional modes in the operating range (say 1.5krmp - 8krpm). Modes close to the rev-limit-rpm can be particularly problematic, depending on the mode-shape, how the limiter functions, the firing order, etc (core breach iminent, capt!). Unless this info were made available the risks of removing a harmonic damper/balancer outweigh the gains, IMHO.

Some change in polar inertia (e.g. lt-wt flywheel) should be ok if OEM torsional damping is maintained.
 
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Well I know for a fact the WRX pulley is harmonically balanced as I have seen it with my own 2 eyes. I don't trust some random email from an 'SOA representative' at all.

But, since I haven't taken my STi pulley off to verify, I can't say it is or isn't. But, based on the WRX's I would be surprised if it wasn't also balanced.

If you did remove your stock pulley, and it has a small rubber ring on the inside of it, then it is harmonically balanced. If not, then the SOA rep is correct.
 

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Where did you get the 20 lb figure for the STI flywheel?

Any idea what is the difference between billet steel and billet aluminum flywheels?
 

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Discussion Starter #13
3 generations of Imprezas

i looked it up with a guy from a subaru-parts department - who then got on the phone with SOA. one of the flywheels (i dont remember which one) GOT WEIGHED ON A SCALE by the guy at SOA while we waited on the phone, and the others specs were from a parts catalog. just thought it would be funny to hear how i got that info - the STi parts are really damn obscure.

Otherwise, nivek, im a technical moron. i dont even know what "billet" means aside from noticing its association with lightweight items.

but im learning new things every day...
 

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FYI for those that are wondering. IF the stock pulley is truly without a harmonic balancer, then it will not affect engine wear. This is according to my father who is a mechanic that has owned several shops in the past, worked for Hollywood on the DUkes of Hazzard, and an opinion I can trust. He has built cars and tinkers with them to no end. So if SOA really meant what it said, no harmonic balancer, then you should have no worries with a lightweight pulley.

He did suggest that the lightweight flywheel could throw a CEL for a number for reasons that were too detailed to go into here. He suggested waiting for someone to experiment and report it. He also indicated that you want to make sure whatever you buy is specifically designed for the STI's 6 speed.
 

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I agree with Nivek's dad. If the pulley does not contribute any torsional damping (i.e. it doesn't have a rubber ring inbetween an inner & outer metal ring) then there's no risk to changing it. If the pulley does, I wouldn't replace it unless I knew the replacement provided for the lost damping, in at least an equal amount.

Reducing/eliminating torsional damping can cause more than just increased wear. The results can be catastrophic! I've seen it and it aint pretty!

I also agree that a simple visual exam will tell for sure - so long as it's the rubber-ring type. "Fluid-Dampers" are also out there, and these don't have the rubber ring, so it's difficult to tell with these by simple inspection whether or not they provide damping. You need some other means (e.g. documentation) to tell.

It seems (to me anyway) unconventional to design the pulley to also serve as the "harmonic balancer", but it's certainly feasable, so I'd do the homework on this one!
 

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i dont even know what "billet" means
olappa - billet refers to a solid "chunk" of metal - This is how these parts began life. The lite-wt association comes from the fact that metal in this form (vs castings, etc) has higher intrinsic strength, thus the part can be made lighter while maintaining the necessary strength for the application. IOW - The same part made from a casting would have to be thicker, beefier, etc (and thus heavier) to achieve the same strength & performance.
 

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A 'rubber ring' or any other more sophisticated assembly is not required to dampen out vibrations (although they may be more effective pound for pound). The harmonic balancer on my '69 Firebird is simply a chunk of steel (that's not even used as a pulley - it's solely for torsional vibration).
 

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Valvetrain - I agree with you, sort of. A solid disk can only affect the frequency(s) of torsional vibration modes (higher mass, lower freq), but contributes no damping per se. Relative motion is req'd for there to be damping. Think of your shock absorbers. The rubber ring allows the inertial (driven) mass on the outside to move relative to the driving mass, bolted to the crank. No relative motion, no damping. In terms of minimizing torsional vibs one can either move the mode out of the operating speed range by changing system mass(solid disk), or damp the mode where it is(rubber ring, fluid-damper, etc).
 
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