This has already been discussed in numerous threads and has been beaten to death.
Here is one of the best quotes out of all of them:
http://www.ft86club.com/forums/showt...armonic&page=6
Quote:
Originally Posted by Infamous Performance
There are dampners, but no balancers.
Some basic info:
Each time the air/fuel mixture inside a cylinder is ignited, the combustion that occurs creates a torque spike that is applied to the crankshaft through the piston and rod. This torque spike is so severe that it not only turns the crankshaft, it actually twists the crankshaft ahead of its normal rotation and then the crankshaft rebounds. This twisting action is known as torsional vibration. When these torque spikes and forces get into phase with the natural frequency, critical torsional harmonic vibrations occur and can be seriously destructive to the bearings and the crankshaft. Dampers are designed to control those destructive vibrations.
Critical harmonic vibrations occur numerous times in a engine’s operating range. Stock rubber and elastomer-type dampers are frequency sensitive “tuned absorbers”, and work at only one critical frequency. In the case of a stock rubber damper, it is tuned for a factory engine’s critical harmonic vibrations. If you change the mass of pistons, rods, or the crankshaft, you change the natural frequency of the crankshaft assembly; therefore, the stock damper is no longer tuned to the new frequency of vibration, and you may be headed for early failure of expensive engine components. Dampers also create heat while they work, and rubber is a poor dissipator of heat. This heat and the exposure to the elements deteriorates rubber, causing it to crack and change durometer, which then leads to inertia ring slippage, damper failure, uncontrolled torsional vibration, and costly engine parts breakage.
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Here are some quick facts:
1 - The OEM part IS a torsional harmonic dampener - period.
It is a classic case of one AND is likely built around specific harmonic frequencies. AND it is HEAVY - one of the adjustable parameters when designing a dampener.
2 - The OEM part is positively, unquestionably MORE EXPENSIVE for the manufacturer to use than one machined from billet Al.
3 - Switching from the OEM pulley to a lightened pulley set WILL result in a noticeable difference in rev up/down
when the engine is decoupled from the drivetrain.
4 - Switching from the OEM pulley to a lightened pulley set (NO Underdrive) WILL NOT result in a noticeable difference in rev up/down when the engine is COUPLED TO the drivetrain.
EXCEPT for the difference in overall VEHICLE weight from the change.
DISCLAIMER: When I use the term "noticeable" above, I mean by a
human's butt-dyno.
Of course you could "determine" there WAS a difference in 1/4 mile times between the two setups, but it would still be in the noise of the measuring equipment (likely in the milliseconds).
Overall - If lightening the rotating mass is SOO damn desirable, why have a flywheel AT ALL?