Lightened Crank Pulley on Subaru Engines (FA20)

[Matt Jones]

I was considering installing a lightened crank pulley on my BRZ. I’ve read endless threads, both pro and con, as far as lightened crank pulleys being bad for engine balancing, no real benefits, etc. Some say Subaru engines are internally balanced, so adding a lightened crank pulley has no negative effect. Can anyone confirm this? Don’t want to throw things out of whack.

thanks

Topic

[Mike]

My best advice is that if the engineers who designed your engine calculated that your engine needs a harmonic damper of a certain mass to do the job, that’s what you should run. You are free to install anything you want, but you would do so entirely at your own risk.

Even though your engine is internally balanced, that doesn’t mean an appropriate harmonic damper isn’t required. (If your engine were externally balanced, the device in question would incorporate an external counterweight and would technically be a harmonic balancer, which does a related but slightly different job than a harmonic damper.)

The proper harmonic damper quells vibration frequencies within the crankshaft at all expected crankshaft rpm. A damper of a different mass could allow these vibration frequencies to coincide (harmonize) with a certain crank rpm, which can destroy your crankshaft.

[Matt Jones]

Thanks, that’s what I’ve heard from different forums. Funny that almost every after-market manufacturer makes a set of lightened crank pulleys, alternator pulleys, tension pulleys, etc.

[Mike]

Oh, maybe I misunderstood your original question.

I don’t think installing lighted belt pulleys has any negative effects, although I kinda doubt that they’ll provide any noticeable benefits.

I was talking about the harmonic damper itself. (The metal and rubber sandwich that bolts directly to the front crankshaft extension. The belt pulley then bolts to the damper.)

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