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Port Plates

MPG Port Plates

Based on our extensive study of airflow we have developed our MPG Port Plates. These port plates dramatically increase the amount of engine torque and horsepower.

Our studies have disproved many long-held assumptions regarding cylinder head porting. The shape of the port, not the size, determines the airflow through any port. Depending on their shape, smaller ports can flow more air than larger ones. This is why many of the new sophisticated race heads have significantly smaller ports than previous high-performance heads. When more air volume flows through a smaller cross-section, the air speed or velocity increases.

Airspeed in cylinder heads is important because it allows cam profiles with later intake valve closing points. Closing the intake valve later, in conjunction with very efficient (High-Velocity) intake ports, increases the volumetric efficiency (VE). This is commonly known as inertia supercharging. Using ports plates, and custom cam profiles can generate VE's in the 105% to 108% range.

Many people think that port plates restrict airflow, but actually port plates allow more air volume to flow through a smaller port. Additionally, they do not require machine work to install.

351C / Boss 302
Intake: On the street, or where midrange torque is important, the Cleveland ports are not effective. At midrange air velocity slows and the vacuum signals pulsing through the ports become confused because of the volume. Due to the slow air speed, fuel drops out of suspension, mixture distribution becomes a lottery, and throttle response is poor. The Cleveland heads need smaller ports, exactly what MPG Head Service delivers with our port plates. Our port plates force airflow into the naturally higher velocity section of the port and produce beneficial effects on throttle response and mixture distribution.

Exhaust: When the exhaust valve opens on a Cleveland or Boss 4-valve engine, the expanding airflow path wants to follow the roof of the port. However, the floor of the port falls off dramatically at the header/exhaust manifold junction, causing the column of air to expand. Whenever a column of air expands, it stops flowing or stalls.

The port plates raise the exhaust port floor approximately 1.5 inches. When the engine RPM is low, the column of exhaust gas wants to reenter the exhaust port (because of 14.7 inches of atmospheric pressure in the exhaust system). This phenomenon is known as reversion and it hurts low RPM torque by diluting the quality of intake mixture in the cylinder. The port plate creates a wall that when the air column tries to turn and reenter the port. The air column strikes the plate and stays captured in the header pipe, where it belongs.

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