What is a fast camshaft and how does it work?
What does a camshaft do?
A camshaft controls the opening and closing of valves in the cylinder head. These valves control the supply of air and fuel to the combustion chambers and the discharge of exhaust gases. The camshaft has cams – raised sections on the shaft – that operate the valves via rocker arms or hydraulic tappets. How long and how far the valves stay open depends on the shape of these cams.
Key terms:
- Cam profile: the shape of the cams determines the timing and elevator of the valves.
- Cam elevator: how far the valve is opened.
- Valve timing: the time at which the valve opens and closes.
- Overlap: the period when the inlet and outlet valves are open at the same time.
What is a fast, hot, wild or sharp camshaft?
These terms are used interchangeably, but mean the same thing: a sporty camshaft with a more aggressive cam profile. This provides:
- Larger cam elevator → Valves open further → More air and fuel in the cylinders → More power.
- Longer opening time → Valves stay open longer → Better breathing engine.
- More overlap → Intake and exhaust are equally open at the same time → Better cylinder change at high rpm.
Effect on engine performance
- More top end power, but less torque at low rpm.
- Restless idle due to longer valve timing and overlap.
- Higher fuel consumption because the engine is optimized for higher speeds.
Example: for example, a standard camshaft opens the intake valves to 8 mm and for 220 degrees. A sport camshaft can increase this to 11 mm and 270 degrees, giving the engine more breathing room.
Why do fast camshafts work especially at high rpm?
At low speeds, a long opening time and lots of overlap is disadvantageous because:
- There is less time to fill a cylinder efficiently.
- There may be air-fuel mixture lost through the overlap.
- The engine idles erratically.
At high rpm, this does benefit because:
- The higher air velocity helps in efficient cylinder filling.
- The overlap allows for better flushing of exhaust gases.
- The higher speed reduces the effect of turbulent running.
In short, a fast camshaft works great on a track, but not as well in an everyday car.
How does variable valve timing (such as VTEC) solve this problem?
A fast camshaft always operates the same way, while systems such as VTEC, VANOS and VVT-i switch between multiple cam profiles.
This is how VTEC (Honda’s system) works:
Low revs: the engine uses a mild cam profile for smoothness and efficiency.
High revs: a more aggressive cam profile is engaged for extra power.
Why is VTEC so smart?
- You have both a quiet idle and lots of top-end power.
- The engine consumes less fuel at low load.
- You get the best of both worlds: smooth ride and sporty performance.
Honda’s DOHC VTEC, for example, shifts to a sporty cam profile from 5,500 rpm, which really sets the engine loose. This explains why many Honda’s are known for their power at high revs. BMW and Toyota are also well versed in this technology.
Fast camshaft versus VTEC
| Feature | Fast camshaft | VTEC (or variable valve timing) |
|---|---|---|
| Power character | Optimized for high rpm | Variable, depending on rpm |
| Low rpm | Restless, less efficient | Smooth and economical |
| High RPMs | Maximum performance | Switches to sport mode |
| Fuel consumption | Often higher | More efficient |
| Ideal for | Track, performance cars | Daily use and sporty driving |
This is how to recognize a car with a fast camshaft
- Restless idling, especially when the engine is cold.
- Higher fuel consumption than a standard engine.
- Strong power building at high rpm, but slow at low rpm.
- Sometimes a louder intake noise due to the longer valve openings.
In VTEC cars, you notice a sudden power boost when the system engages, often with a recognizable “kick-in” feeling.
Can you combine a fast camshaft with VTEC?
Yes! Honda, for example, has Type R engines with an aggressive VTEC profile optimized for performance. Tuning companies sometimes combine a fast camshaft with a VTEC system, keeping an engine smooth at low revs and delivering extreme power at high revs. However, this requires custom ECU mapping and sometimes reinforced valve springs.
The main message: hot/wild/sharp/fast cams are all the same. Various terms are mentioned online, but you now know they are the same principle.