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| If your car is OBDII equipped and has a misfire detection crank angle sensor trigger on the flywheel make sure that your replacement flywheel has one like this JWT 350Z unit or your check engine light will come on. |
One of the myths about lightweight flywheels is that they make more power. A flywheel does nothing to make more power! A light flywheel does speed the time it takes for an engine to accelerate through a rev range and speeds acceleration. On an inertial type dyno like a Dynojet where a computer derives power and torque from measuring the time it takes to spin a drum of a known mass up to speed, a light flywheel will show up as a gain in power. This isn’t really increasing an engines power, its freeing up more of the engines power that would be used to spin up a heavier flywheel. A general rule of thumb is, one pound taken from the flywheel affects acceleration like 4-8 pounds taken off the chassis. There are other benefits to a light flywheel as well, by helping the revs drop quickly when the throttle is lifted, a lightweight flywheel is easier on the transmissions syncros and helps speed shifts.
As in most things automotive, you don’t get something for nothing. A light flywheel usually requires a little higher revving and a little more clutch slipping to get underway from a stop. Sometimes there are more vibrations and noises from the engine or transmission as the stock flywheels mass often helps damp these out. Rarely, extremely heavy cars with a lot of grip might launch harder with a heavier flywheel. For these reasons, road racers try to strive for the lightest possible clutch and flywheel combination but drag racers sometimes run slightly heavier flywheels, albeit still lighter than stock. Most of these drawbacks are easily forgiven and compensated for by the enthusiast driver.
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| A chromemolly steel flywheel takes advantage of the high strength of the material to enable the flywheel to be made very thin like this ACT part. This reduces the inertia of the flywheel considerably. The thin bell like structure of a steel flywheel can sometimes make them more noisy than an aluminum one |
A typical light flywheel weighs from 5-12 lbs. It’s typical for a light flywheel to be about 8-15 lbs lighter than stock as stock flywheels can range from about 15 to 35 lbs. Most of the better light flywheels are made of either billet aluminum or forged chromemolly steel. Aluminum flywheels usually have steel friction surfaces and starter ring gears that can be replaced as they wear. These are handy features, especially for those of you running aggressive and abrasive metallic clutch discs. Chromemolly flyweels can be resurfaced a few times to restore worn friction surfaces and are often a little bit noisier as the hard thin metal can ring like a bell when subjected to vibrations. Fine flywheels are made either way.
Please for safety sake only get light flywheels that are SFI approved for burst strength or are from a reputable manufacturer with a lot of experience and a good reputation. Since a rapidly spinning flywheel can explode with enough power to blow a car in half (God hope your body is not in the way of the fragments), cheap is not always better here. This is the main reason I do not recommend machining your stock flywheel in an attempt to save weight.
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| This explosion shows how much energy an exploding flywheel can release. In this historical explosion, the flywheel blew Don Garlits Top Fueler in half along with his foot and a spectators arm. The tragic accident prompted Garlits to design the first mid engine Top Fueler and the rest is history. |
