Toyota's partial lean-burn system
The latest Toyota engine, featuring turbocharging and supercharging and used in their FXV concept car, has the inlet ports for each cylinder separated into two — one straight and one helical. At high engine speeds, both ports are open, but at low loads, a control valve in the straight port remains closed. All the mixture goes down the helical port, creating a swirl effect in the combustion chamber. This swirl mixes the fuel and air more fully. The fuel content in the mixture is very finely metered by individually controlled injectors to increase clean running still further.