Performance upgrades can be time-consuming, but when the ultimate goal is to get more power, it makes the whole ordeal worthwhile.
There are two main factors at play when it comes to performance – torque and traction. You can spend thousands on modifications under the bonnet, but getting that power down to the wheels is what counts.
No matter how much bhp the engine puts out, it all goes to waste if it’s matched with a wimpy drivetrain that’s just not designed to handle the extra power.
Parts tasked to do that job are the flywheel, clutch, differentials, gears and driveshafts. These are referred to as car drivetrain parts.
Their job is to efficiently and smoothly transfer engine power at different revs and speeds down through the axles and wheels.
But with more raw muscle in the mix, stock parts just can’t cope. Here’s everything you need to know if you plan to buy aftermarket car drivetrain parts.
Flywheels
Flywheels are what connect the crankshaft to the clutch and transmission. This is in cars with manual transmissions (autos have flexplates connected to torque converters). The flywheel’s job is to maintain inertia as the engine spins.
Heavy flywheels perform well here but struggle when there’s the need to abruptly increase or decrease speed. For this purpose, changing to a lighter flywheel can change the engine’s power band, allowing it to spin more freely and faster.
Custom aluminum race flywheels might not be what you’re looking for in your daily driver (that you also chuck around the track on odd weekends), but a lightened steel flywheel can suit both roads and track usage without the instantaneous loss of throttle (and a chance of stalling) once you lift your foot off the pedal.
A lighter flywheel done right can improve throttle response and acceleration, and is an inexpensive modification in the sea of vehicle modifications.
Clutches
Clutches connect the engine and flywheel with the drive shaft. They consist of two basic parts – the pressure plate assembly that is fixed to the flywheel, and the friction disc attached to the input shaft of the transmission.
With the engine running, the flywheel and pressure plate spin together. Torque from the spinning assembly is then transferred from the flywheel to the transmission input shaft.
With the clutch pedal depressed and the clutch disengaged, the pressure plate lifts off the friction disc by way of a diaphragm spring and no torque is transferred.
Stock clutches start to slip and judder when the increase in torque with previous engine mods also increases friction (and accompanying heat) on the friction disc.
Though the right amount of friction is needed for everything to work, too much can make jittery starts a common occurrence. Adversely, a clutch with not enough clamping force can’t engage the torque sent out by the engine, so there’s a sudden loss of power.
Upgrading to power and performance clutches allows for more bite. Frequently changing gears, with the clutch pedal depressed and released in quick cycles produces a lot of friction and heat and this is what wears down stock clutches needing to push more torque.
Metallic and ceramic plates in performance clutches (in what are known as clutch stages) hold up better here and have more clamping force in the diaphragm springs.
Performance clutches also benefit from lighter weight. With less mass in the clutch assembly, the engine needs to work less to get things moving. Weight is reduced by using lighter metals in the pressure plate, particularly aluminum, or titanium in race clutches.
What is important is matching engine power output with the friction the clutch can take, while reducing excessive heat and resulting wear.
Performance clutches are rated for nominal engine torque output, and this is what to go by when swapping out the stock clutch assembly.
Transmission and Gears
There are a variety of transmission types, but for motoring purists and those that enjoy the involvement of driving, let’s explain the intricacies of manual transmissions.
These are more complex car drivetrain parts. Manual transmissions consist of an input shaft stemming from the clutch and driving the gears along the countershaft at the same speed as the engine.
Countershaft gears are connected to gears in the output shaft, and these are in different sizes. To engage and rotate the gears, a series of dog clutches (different from the friction clutch) on the output shaft locks the gears into place along both shafts. Synchronizers ensure that the speed at which the gears are spinning is balanced.
Power from the engine and the input shaft is first transmitted to the countershaft and this, in turn, engages the different gears on the output shaft.
This happens with the input from the driver by shifting the gear stick, which engages the dog clutches positioned along the output shaft in selecting the right gear.
For performance upgrades and modifications, the gear ratio is crucial. This is the difference in size between the gears on the countershaft and drive and the gears on the output shaft.
Gear ratios are worked out by dividing the number of teeth on the countershaft gears by the number of teeth of the output gear.
The speed at which the output gears spin is the same as that of the wheels. On low gears, such as 1st and 2nd, the output gears are bigger and with more teeth, meaning they also rotate slower, but provide the needed torque for moving the vehicle from a standstill.
For quicker acceleration then lower gear ratios are better. Output gears that are more closely matched (think first, second and/or third gear) yield faster 0-60 mph times. Relatively effortless and efficient cruising at highway speeds is achieved where the output shaft is spinning at roughly the same speed as the engine (with a countershaft and output ratio of 1:1).
Differentials and LSDs
In front-wheel-drive cars, the transaxle along the transmission transfers power to the wheels. In rear-wheel-drive cars, the differential is located in the rear axle and connected to the transmission with a driveshaft.
For 4WD and AWD cars, an additional central differential or transfer case allocates the right amount of power to the front and rear wheels.
The role of differentials is to allow wheels to spin at the correct speed (outside wheels cover larger distances and hence spin faster than inside wheels) when turning. Without a differential, turning would be impossible.
Performance vehicles have better handling in turns with an included Limited Slip Differential (LSD).
This limits the amount of wheelspin and the torque sent to a wheel that loses traction. For better stability, the LSD instead sends torque to the wheel that is firmly on the road.
LSDs may be overkill on standard cars used in everyday driving, but for cars you’d regularly use on a track, an LSD will give you faster cornering and more grip.