Nissan 240SX - Performance
The drivetrain (flywheel, clutch, transmission, driveshaft, and differential) is where much of a carís horsepower is lost. It is important to upgrade the drivetrain if you increase engine power or drive aggressively.
The first drivetrain upgrade I would make is replacing the 2-piece stock driveshaft with a single-piece part. An aluminum or carbon fiber driveshaft will be lighter and more durable than the stock piece. Aluminum is less expensive, but carbon fiber is lighter and will shatter if it comes loose or begins to break. An aluminum driveshaft is more likely to destroy the underside of your car if it comes loose since it will not disintegrate like the carbon fiber shaft. Drive Shaft Shopís 240SX/Silvia Aluminum Drive Shaft is a good choice for the 1989-94 240SX. It is 40% lighter than the stock piece and rated at 800 hp. The price is $450.
The next drivetrain part that should be changed is the clutch. Choosing a clutch is important because it will strongly affect your carís performance and how it behaves on the street. An aggressive clutch is necessary if you are adding significant power, but it will make pressing the clutch more difficult. Also, more aggressive clutches tend to have an on/off button feel instead of a smooth feel, which makes normal driving annoying.
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The engine output is connected to the flywheel. A lighter flywheel will allow the engine to rev up faster and waste less power on spinning the heavy stock flywheel.
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A differential allows the rear wheels to spin at different speeds in a corner while power is being applied to them. The outside wheel must spin faster since it travels a longer distance than the inside wheel. A Limited Slip Differential (LSD) performs the function of a regular differential but also locks the rear wheels together when one of the wheels begins to slip. Without an LSD, when a wheel slips, the majority of the power goes to that wheel. The power is wasted, and the car does not move forward. To see why this happens, read How Differentials Work from howstuffworks.com.
Cornering ability is improved when an LSD is installed. The two main types of LSDs are viscous LSDs and clutch-type LSDs. A viscous LSD works by using a friction-sensitive fluid positioned between plates connecting the left and right axles. If the axles spin at different speeds, they heat up the fluid. The fluid expands, which locks the two axles together.
The clutch-type LSD works by locking the rear wheels together by using a set of clutches and springs. In order for one of the wheels to spin faster than the other, that wheel must overpower the clutch. This is easy when both wheels are gripping in a corner. However, when one wheel starts to slip, it does not have enough torque on it to overpower the clutch. Therefore, the two wheels are locked together. The stiffness of the springs in the LSD can be used to adjust when the LSD begins to work. Generally, clutch-type LSDs are more durable, responsive, and adjustable. Therefore, most aftermarket LSDs are clutch-type. However, these LSDs require regular maintenance unlike the viscous LSD. Certain models of the 240SX came with a viscous LSD (see Optional Performance Equipment).
The S15 came with a helical (AKA Torsen) LSD, a third type of LSD. However, even if your car came with a viscous or helical LSD, it is wise to upgrade to an aftermarket clutch-type unit. It will be better suited for high horsepower engines and aggressive driving.
When researching various LSDs to purchase, you will see the terms 1-way, 2-way, and 1.5-way differentials. A 1-way differential only locks on acceleration. A 2-way locks on both acceleration and deceleration. A 1.5-way LSD is the same as a 2-way except that the lock-up rates are different for acceleration and deceleration. The 1.5-way LSD makes the car easier to turn on corner-entry as compared to using the 2-way.
As a rule of thumb, research the manufacturers that supply parts to racing teams if you are unsure of which company to go with. For example, many racing teams use Kaaz and Cusco LSDs.
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