420motorsport. Belts & Pulleys – Timing Belts, Tensioners & SC Pulleys

Belts, pulleys and tensioners work together

The crankshaft drives accessories such as the alternator and, where fitted, a supercharger via drive belts, while the timing belt keeps the camshafts and crankshaft in sync. The diameter of the pulleys determines how fast the accessories spin. Belt tensioners maintain the correct tension so the belt doesn't slip or wear unnecessarily. A slipping belt can cause squealing, uneven charging or lower boost on a supercharged engine.

How to choose pulleys

When you choose pulleys, the right choice depends on several factors:

Ribs and profile: must match the belt, e.g. 6, 7 or 8 ribs, or teeth as on a GT2 toothed pulley.

Diameter: a smaller supercharger pulley can increase supercharger speed and therefore boost. This typically requires adapted engine management and fuel delivery, as well as a belt of the correct length.

Mounting: bolt pattern, width and space in the engine bay.

Weight: a lightweight alternator pulley, e.g. from Torque Solution, reduces rotating mass. However, a changed diameter can also change the alternator speed.

ATI states the diameter and number of ribs in the product name. Some of their pulleys are stock size, others have a percentage change. KraftWerks offers, among other things, pulleys for Rotrex superchargers.

Timing belt and maintenance

The timing belt must be replaced according to the car manufacturer's interval. On many engines, the valves and pistons can collide if the belt skips a tooth or breaks. It's therefore a good idea to replace the tensioner and idler pulleys at the same time. A timing belt kit typically includes these parts. Our range of timing belts also includes racing versions, such as the Gates Racing Performance Timing Belt. Always check the part number against the engine and model year, and tension the belt according to the manufacturer's instructions.

Frequently asked questions

What is the difference between a drive belt and a timing belt?

The drive belt is often a ribbed belt that drives accessories such as the alternator and, where fitted, a supercharger. The timing belt has teeth and keeps the camshafts and crankshaft synchronised. It must therefore be replaced at a fixed interval to avoid engine damage.

Can a smaller supercharger pulley give more boost?

Typically yes, because the supercharger spins faster. How much depends on the supercharger and engine, and the change normally requires adapted engine management and fuel delivery. Also check belt length, belt wrap and whether the tensioner suits the setup.

Why does the belt squeal?

Squealing is often caused by the belt slipping. The cause can be a worn or glazed belt, incorrect belt tension, a weak tensioner or misaligned pulleys. Check the entire belt drive before replacing a single part.

Do modified pulleys need approval for inspection?

It depends on the product and the car. If the change increases engine power, e.g. through higher boost, it may require documentation or approval. Check the requirements for the specific part number and your car before fitting.