Combustion Air Management

When developing a high performance engine, managing intake air and exhaust flow is one of the most important factors. Managing airflow requires more sophistication than simply adding high output turbochargers or intercoolers. Managing airflow actually begins with the design of the cylinder head.

The traditional technique of requiring high air turbulence within the combustion chamber to ensure proper mixing of fuel and air is created by intake passages which impart a twisting action to the flow of air as it enters the cylinder. However, this technique restricts the maximum airflow through the cylinder, limiting yacht performance.

Modern technology achieves proper mixing of fuel and air by using specially developed intake ports, innovative fuel injector tip designs and high injection pressures of more than 20,000 psi. This design, together with four valves per cylinder, results in a free flowing cylinder head, maximum airflow and maximum yacht speed and acceleration.

The intake ports are very short which avoids the incoming air charge being heated up (the cool incoming air is not exposed to long hot metal passages). This cooler intake air provides more power and reduces stress on cylinder components. That gives peace of mind when you’re far away from port and increases engine life.

Exhaust passages are also short to avoid losing heat into the exhaust passages in the head. Therefore, maximum exhaust heat is retained for maximum turbo-charger performance and maximum yacht speed.

Turbochargers which are matched to a yacht’s intake air requirements when on the plane, normally don’t provide enough boost pressure at low speeds, resulting in sluggish performance. Turbochargers which are too small, provide good acceleration at low speed but choke the engine at higher speed, limiting maximum yacht speeds.

To overcome these problems a number of manufacturers are now building high performance yacht engines with various designs of sequential turbo-charging.

Several air management valves are strategically located in the intake and exhaust systems. Electronic controls monitor all phases of engine operation and open and close the valves.

When yacht speeds are low and maximum acceleration is required, all exhaust gases from all cylinders are routed to only one of the turbo-chargers on the engine. This technique provides instant and significant turbo boost at low speeds, resulting in excellent boat acceleration. In addition, even at steady state speeds below planing speed, all exhaust gases flow through only one of the turbo-chargers. This ensures high turbo-charger speed for good airflow and virtually no exhaust smoke.

Once the yacht is on the plane, the air management valves open and both turbo-chargers come into play, providing the air needed for maximum yacht performance.

When maximum required turbo-boost pressure is reached, a waste-gate (bypass valve) in the turbo-charger opens to control maximum boost and reduce cylinder loads for increased engine life.

These airflow techniques also incorporate the use of a turbo-charger sensor, which can measure turbine speeds in the order of 100,000 rpm.