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"For the current Ultra Race lineup, gains of 6 to 14 HP and 5 to 12 lbs.-ft. on normally aspirated engines and 10 to 18 HP and 7 to 14 lbs.-ft. on forced induction engines can be seen. These are average gains. Higher gains can be realized on any modified engine.
These power gains are obtained in a few ways. First, and most important, is the weight loss. There is an average of 2.7 HP gained from every pound lost off the crank shaft. 85% of our gains are from weight loss."
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Well what can I say... they certainly seem to be giving out incorrect information on their website. I can't say whether they're intentionally misleading you or just mistaken, but the information isn't accurate. Think about it this way: reducing crankshaft inertia is basically the same as reducing mass anywhere in the vehicle (except that the effect is magnified by the crankshaft speed). Can you affect power by eating less food when you stop at McDonalds? By wearing lighter clothes? By taking the spare tire out of the trunk? Of course not. All you'd change is the vehicle acceleration. You can calculate an amount of horsepower that would be required to produce the same change in acceleration, but that doesn't mean that you're actually producing that amount of extra horsepower.
Even if you give them the benefit of the doubt, and assume that they just mean "equivalent horsepower," their rule of thumb is incorrect. The place where you remove the mass from the crank is far more important than how much you remove - so to say that there is some given amount of horsepower for every pound removed is just silly. The farther the mass is from the crank axis, the more important it is. If they were talking about changes to crankshaft inertia, in lbm*in^2, the statement would make more sense, because then they'd be including the all-important radius, but they aren't.
Furthermore, if we consider "equivalent hp" gains due to reduced inertia, the number doesn't depend on baseline engine power. If you look at accessory drive power (the place where they actually do see improved power instead of just acceleration), again there is no change due to baseline engine power. So the claim that engines that are more powerful initially will see a bigger benefit seems completely bogus.
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If you have ever held a Harmonic Balancer in your hand those things are pretty heavy they are like made out of cast iron they are very brittle if you drop them they will crack very easy.
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I have held a "harmonic balancer" (more accurately: torsional vibration damper). What isn't clear from your statements or the documentation on the site is whether or not the tv damper is removed when you install this pulley, but it sounds to me like it IS removed. I don't remember whether or not the tv damper is integrated into the crank nose pulley on your vehicle - is it?
The reason that it is important is fairly simple. The TV damper is used to reduce the amplitude of torsional (twisting) vibrations along the crankshaft. The loads that the crankshaft sees due to these vibrations (when the damper is working properly) are typically about four times the "static" (no vibration) loads on the crank. If you get rid of the damper, these vibratory loads will get worse, possibly resulting in the failure of the crankshaft (a broken crank). The stiffness of the rubber portion of the damper, and the inertia of the ring attached to the rubber portion, are picked during engine development to give desireable damping behavior. It's not guaranteed that in every application removing the damper will result in crankshaft failure, but I have trouble imagining an application where the damper is superfluous.