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Message: <blockquote data-quote="koolspyda" data-source="post: 679261" data-attributes="member: 2832">to address the issue why & how does a lighten flywheel helps.for the library; Lighten flywheels'Most manufacturers make the stock flywheel very heavy. This makes the engine very smooth and enables it to retain energy at part throttle cruise and up long grades for better fuel economy.An Aluminum flywheel goes completely the other direction with almost no weight. This lets the engine rev up very quickly and allows the engine to work easier due to the reduced weight spinning around on the back of the crank. This is fine as long as you are at full throttle and wide open throttle all the time like in a Road Race or Drag Race only car. As soon as you let off the gas the engine RPM drops faster than stock and the car slows down (engine braking). In a road car this causes surging and bucking at cruise speeds and poor driveability and clutch engagement.If we measured the power output of an engine first with light flywheel and then again with the standard part on an engine dyno, no change in power will be seen to occure. At first it appears that the light flywheel has done nothing and was a total waste of cash. This is not the case. A dyno that shows max power at constant revs does not demonstrate what occurs to an engine's power output in real life situations - like acceleration. If an engine is accelerated on a dyno ( we are talking about a rate of around 2000rpm a second ) it would show a power output of around 20%-25% less than at the constant rev state. The reason for this is that when accelerating a vehicle the engine not only has to push the total mass of the car but the internal components of the engine need to be accelerated also. This tends to absorb more power as the extra power is used accelerating the internal mass of the engine components and is why a motor accelerating on a dyno will produce less power than at constant revs. Also it must be remembered that the rate of acceleration on the engine internals is much greater that the rest of the car. This would then suggest that by lightening the flywheel, less power would be required to accelerate it and therefore more power would be available to push the car along. Now, it may seen unbelievable that by removing a few kilos from the flywheel a noticeable difference to a 1000+ kg cars acceleration will be made. In fact the difference is quite noticeable and the secrete behind this is hidden within the gearbox. Everyone knows that cars accelerate at a greater rate in low gears, this is because a cars gear box basically a mechanical leaver and just like when using a leaver to lift a heavy object, the gearbox reduces the mass of the car that the engine sees. For example, in first gear an engine will see the cars mass as only around say 100kg but the engine internal mass would still remain around 20+kg . Turbo cars are exceptionally critical to flywheel weight. Too light a flywheel will make the car rev faster and possibly come on boost faster but that is only half the issue. When you let off the gas to shift the car will drop off of boost just as quickly causing a poor transition when you come back on the throttle.</blockquote>

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