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Performance Flywheel

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Clutch flywheel

What is a flywheel

In a car's clutch, a flywheel connects to the engine, and a clutch plate connects to the transmission. You can see what this looks like in the figure below. So what is a flywheel? The car flywheel consists of varying weights on opposite sides of the engine's crankshaft. When your foot is off the pedal, the springs push the pressure plate against the clutch disc, which in turn presses against the flywheel. This locks the engine to the transmission input shaft, causing them to spin at the same speed.

Once the crankshaft makes a full rotation, the varying weights of the engine flywheel, which are evenly spread out on the crankshaft, will keep the pistons moving up and down. The flywheel will stop rotating once the electrical power is cut to the engine. When the car key is turned off, it breaks the electric circuit from the battery and stops the electrical current traveling to the distributor. Without the distributor distributing electricity to the spark plugs, the pistons will no longer fire downward and support the flywheel spinning.

Performance flywheel

Flywheel Lightening

Lightening the flywheel - the flywheel on a car works in a similar way to the wheel in the toy cars you used to rev up and release and let it zoom off. The heavy wheel located between the engine and the gearbox builds up rotational force with speed and momentum. Effectively storing the energy and helping the car resist changes in engine speed - good for cruising at a steady speed but bad when you need a fast engine response. Drawbacks - it takes effort to get the wheel rotating and stops the engines revs increasing or slowing down quickly. A light flywheel takes strain off the engine and allows the engine to rev more freely, as a bonus as there is less weight the engine is able to release more power. You'll notice a race-tuned engine increases and decreases revs a lot more quickly than a standard engine. The big downside to a lightened flywheel is that engine momentum or inertial spin is reduced - most noticeably on a hill.

Lightweight flywheel

The lighter the engine flywheel the faster engine revs will rise and fall but you will lose momentum on a hill more quickly. Whereas the momentum in the engine is maintained with a heavy flywheel the momentum is reduced and the hill has a much more direct effect on the engine output. Best used in a race situation where the track is flat with a demand for fast engine speed changes and the engine has been tuned to output power matching the flywheel capacity (high revving).

What is flywheel

The driver will often heel and toe gearchange and braking taking advantage of the greater responsiveness from the engine. Various weight of flywheel on a car are available allowing you to get the best torque/free revving capabilities. Different grades of performance flywheel are available for different situations have a chat with our members in the Torquecars forum to discuss your required application. If you feel tempted to make your own light flywheel by drilling holes in it torquecars urge you to reconsider.

If you are serious about getting a lightened flywheel to get a free revving engine try a carbon fibre drive shaft. These will rotationally flex more that their metal counterparts and reduce strain on the engine. If a metal drive shaft breaks you will soon know about it as parts are thrown through the car! A carbon fibre one is stronger but if it does break it will 'broom' into 'harmless' fibres and little damage will be done to the car.

Is Lightweight Flywheel Better Than a Heavy One?

What is flywheel

Those who say their car feels quicker with a heavy flywheel are revving the motor above the correct gear/wheelspeed amount, and "dumping" the clutch. The heavy flywheel stored energy, and then transferred it to the transmission/wheels. Technically, during this engagement, the stored energy plus the engine input energy is more than the engine makes alone. The critical thing to realize is that this only holds true during the period of clutch engagement and is a "false torque" sensation. That "false torque" sensation tricks human perception into thinking the car has more power, when the flywheel torque measurement of such an engagement style shows that the "false torque" jump up is immediately followed by a sub-normal torque dip as the heavy engine flywheel requires more energy input to re-accelerate than the lightweight flywheel.

The "false torque" effect of the green line clutch dump is obvious; during, and only during the clutch engagement up to 2500rpm, is the energy that the performance flywheel has stored being transferred to the drivetrain. After 2500rpm, it uses even more energy to re-accelerate. Contrast this with the red line smooth engagement which has more torque at the wheels everywhere above 2500rpm. Even though that graph is showing two successive runs on the same car, the point regarding the "false torque" effect of the heavy OE flywheel is exactly the same. This explains a few car aceessories where magazine dyno tests are mistakenly showing torque loss. So you see, this is the reason why a lightweight flywheel car will walk away from a heavy flywheel car every time, regardless of how the initial clutch dump may "feel" stronger with the heavy flywheel.