Shift Kits

Start with the clutch

The clutch is usually the first drivetrain part to give up after a power increase. Clutch kits are rated by the torque they can hold, in N·m or, from Japanese makers, often kgf·m (1 kgf·m is 9.81 N·m). Choose a rating comfortably above the engine's torque, but not far above it for a road car: more clamp load usually means a heavier pedal and a less forgiving take-up.

• Facings: organic facings engage smoothly and suit the road; metallic facings hold more and take heat better, but bite more suddenly.
• Plates: a twin- or triple-plate clutch holds more torque at a given diameter, so it can be smaller and lighter. Expect a sharper engagement and some rattle at idle.

A lighter flywheel lets the revs rise and fall faster, at the cost of a lumpier idle and more care pulling away. Braided clutch lines keep the pedal consistent when the system gets hot. ORC, Nismo, OS Giken, Exedy and ATS make clutches for many Japanese cars; choose your car with the car selector to see what is listed for it.

Limited-slip differentials

Most performance LSDs from Cusco, Nismo, OS Giken, KAAZ and ATS are plate types, sold by how they lock:

• 1-way locks under acceleration only, and is common on front-wheel-drive cars.
• 1.5-way locks fully under acceleration and partly when you lift off: a balance for road and circuit.
• 2-way locks under acceleration and deceleration, which steadies the car braking into a corner but adds understeer on entry; a usual choice for rear-wheel-drive circuit and drift cars.

Initial torque, in N·m or kgf·m, is the preload that resists the two wheels turning at different speeds before any drive is applied. Higher initial torque locks harder, chatters more in car parks and wears tyres faster at low speed. Plates wear and the preload falls with them, which is what LSD repair parts restore.

A plate LSD needs gear oil suited to it. Use the viscosity and grade the LSD maker gives, such as an SAE 75W-90 or 80W-140 to API GL-5. LSD gear oil from the LSD makers is blended for their units.

Gearbox and shafts

Shift kits shorten lever travel, and gear sets change ratios. Reinforced axles and driveshafts suit cars that launch hard on sticky tyres. Clutch and differential work is safety-critical: have it fitted by a workshop that knows the car.