What are the disadvantages of a lightweight flywheel? The flywheel mass is required to dampen the speed fluctuations of the crankshaft created by the power pulses. In reducing the mass of the flywheel there will be greater speed fluctions (torsional vibrations) transmitted to the transmission. Additionally, flywheel inertia provides some aid in getting a heavy car moving from a standstill reducing the amount of clutch slip required. And lastly, flywheel mass acts as a heat sink for the clutch and therefore a lighter flywheel will potentially cause the friction disc to run at higher temperatures in certain situations.

After installation of the lightweight flywheel I am hearing some noise on deceleration in gear, is this normal? Yes, this is due to the increased torsional vibrations being transmitted to the transmission main shaft. Gear tooth backlash allows the teeth to vibrate creating a noise that is sometimes misinterpreted as a bad bearing or wear pattern issue in the transmission. The noise may be worse when the fluid temperature gets hot due to the reduced damping effect of the fluid.

Will a lightweight flywheel cause a check engine light to set? There is a potential for the ECU to set a misfire DTC and turn on the CEL with a lightweight flywheel. This occurs because of the nature of the ECU's misfire monitoring. It looks at crankshaft speed variations to determine if one or more cylinders may not be firing properly. Becuase of the reduced flywheel inertia the crankshaft speed will naturally fluctuate to a greater extent and can be misinterpreted as a misfire. The lighter the flywheel/clutch assembly the greater the potential for the ECU to be fooled.