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Lightened Crank Pulley

Basically what drives the alternator, water pump and other accessories is the crankshaft pulley, which spins as the crankshaft revolves. For example a smaller, lighter pulley always accelerate faster than a larger, heavier pulley due to its lesser mass and smaller radius. All other components driven by the crankshaft pulley exert load on the former. The said load is proportionate to the circumference ratio of the two pulleys. The load is higher when the size of the crankshaft pulley is larger than the pulley it’s driving and vice versa.

In order to operate the various components, a portion of mechanical energy the engine produces is needed to overcome both the moment of inertia of the pulleys and the total load exerted on the crankshaft pulley. This leaves lesser energy for the engine to turn the transmission, the driving wheels and to accelerate the vehicle hence some fuel savings when driven sanely. 

A lightened crankshaft pulley helps in reducing the energy consumption during the operation of the engine. Mass reduction is achieved by using lighter material and the moment of inertia can be further reduced via under-sizing, which also reduces the exerted load. Torque and Horse-Power gains are therefore better than the stock OEM metal pulley.

However, the momentum of a stock NA engine can be greatly affected with an overly lightened pulley, while the efficiency of the various components can also be affected with an overly undersized pulley. Jerky gearshift and under charging alternator are symptoms of over lightened and severely undersized, respectively.

The mass of a lightened crank pulley for a stock car either equipped with an automatic gearbox or manual gearbox should not less than 1/3 of the original mass. While for the diameter size, it is recommended not less than 90% of the original size.

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Anonymous said...

Hi Ben!

I was hoping to get your advice, I have a problem with my satria neo, when the rpm reach 2500-3000 the car jerks, at first i thought it was the spark plugs, changed them but the problem didnt go away, the crankshaft is in good condition, so now I think the problem might be coming from the gearbox, by the way it's an auto.

Ben said...


You may check the TPS.