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Discussion Starter · #1 ·
i'm thinking of getting light pulleys first. I'd like to get underdrives, but i spend a lot of time in L.A. traffic (crawling at under 10 MPH, A/C on, radio on) and i'm not sure that underdriving my alternator would be a good idea...although maybe there's a way to underdrive the p/s and water pump and NOT the alternator....

anyway i've been told that since you're taking away a lot of rotational inertia by lightening your drive pulley and flywheel that normal driving becomes much more difficult and requires more work to keep from stalling. Anyone out there have any experience with this?
 

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i have the vishnu underdrive pulley, and so far no problems with dimming light at stop or idle. definetly worth it, the difference can be felt immediately
 

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Are you guys at all worried about crank fatigue with UDP installed? What did Subaru use for a harmonic damper?? Thanks.
 

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Discussion Starter · #5 ·
from what I've read, the engine is actually very well balanced for sub-8000 use, and MOST of the noise comes from the heavy drive pulley, so if you eliminate it, the harmonic balancer becomes unnecesary....
 

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Larger engines, like V8's have a "harmonic dampner," which is a mass located in a particular location on the crank pulley, to dampen vibration so as to avoid stressing the crank.

Crank=crankshaft

Fatigue failure is when a material is repeatedly loaded an unloaded which will eventually lead to plastic deformation and/or cracking. Fatigue failure is most often associated with vibrational loads.

The Subaru flat-four doesn't have or need a harmonic dampner.

-Jim

dark_rex said:
:confused:

help! harmonic damper? is that for sound?

please explain the crank fatigue.

dR
 

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PlatinumWRX said:
Larger engines, like V8's have a "harmonic dampner," ...
The Subaru flat-four doesn't have or need a harmonic dampner.

-Jim

Umm, actually, the stock WRX crankshaft pulley does indeed have a harmonic dampener. Whether it's really necessary, is the subject of continuing debate.
 

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Correct me if I wrong (please), but I thought that the Subie flat four didn't need a balancer (since it's horizontally opposed), but that it would still need a harmonic dampner. I believe that the vibrations (however nil they are) would still lead to some harmonics in any system, thus the need for the harmonic dampner.

BTW, this is what caused my crank pulley pin to sheer on my Montero. Got it fixed and traded it in the same week. Money I didn't want to have to spend...:(
 

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The "dampener" is used to isolate NVH levels. It is not a problem for the engine to remove it. Only more vibration from the accessories will transfer to the car itself is all. Same debate went on in the Honda camp for years. I've used them on cars with over 100,000 miles and revving to 9800 RPM. Never had one single problem. Japanese motors are incredibly well balanced, especially the boxer motor in the WRX.
 

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Discussion Starter · #10 ·
OK...so now that we've put to rest all the questions regarding the safety of this mod...will the car still be drivable? Someone told me that I'll be stalling at every light if I take off that much weight, or I'll have to rev the motor higher and slip the clutch more resulting in premature clutch death.
 

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The pulley is no problem. The flywheel is another issue. We are testing many units and they do seem to stall on occasion although rarely. We are adjusting idle and seeing if we can tune this problem out at the ECU. It definately is worth it though. Holy fast revving batman!
 

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Plat- you needed to add terms like: work hardening, and ductile and brittle failure.;)
I just love speaking engineer.
 

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Since you testing many of them Dan, which one is working the best so far or is it too early to tell?

Carlo
 

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Have you tried the Fidanza flywheel yet? It's supposed to be only 9.5 pounds.

Is there a point (in your oppion from testing) that too light a flywheel causes problems?

Oh, yea, one more question: I've been looking for hp gains from flywheel replacements but can't seem to find any dynos or solid numbers. Anybody have anything like this or know where to find it?

Carlo
 

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if you guys are interested in Fidanza flywheels there's a relaly good deal posted on www.importhookup.com. M2s flywheel was just posted on their website recently too and you guys can probably look into that.
 

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I never use aluminum. It has many problems. The aluminum and metal have to be attached somehow and those fasteners have been known to fail. The fact that aluminum and steel have differenent expansion rates further complicates the issue. Bottom line, use chrome-moly. There's a reason NO Japanese manufacturer uses anything but chrome-moly. If the alluminum unit fails, it will take not only the clutch and trans with it but also can be harmful to the occupents of the car.
 

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God said:
The aluminum and metal have to be attached somehow and those fasteners have been known to fail. The fact that aluminum and steel have differenent expansion rates further complicates the issue.
I imagine that the differences in the coefficiences are the result of the fastener failures. The two definintely have different heat capacities, expansion rates, etc. Not a good idea, IMO, to mix metals in this type of application (judging from a "scientific" type perspective).
 

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Well, I have the Fidanza flywheel in my car, I like it, and it certainly revs faster, and seems very streetable. Of course, when I first got it installed with my Exedy clutch, I stalled it.

Fidanza has been making aluminum flywheels for years..... although I agree with some of what God is saying, I don't think Fidanza would have been able to stay in business this long, if there were any serious issues with aluminum. Maybe it also depends on the Manufacturer, and what processes they use.....

I'm installing the Vishnu UD pulley today. I'll let you guys know how it seems to work..... If I stall, I'll just up the idle a little.....

Brett
 

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Discussion Starter · #20 ·
I thought aluminum flywheels use non-metallic materials to deal with the issue of different expansion properties of metals...and can you get a cro-mo flywheel that's light enough to make the $700 or so operation worth it? With aluminum, you're practically cutting the weight in half.
 
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