The __________ should always be the same size or slightly larger than the cylinder head port diameter.

• A. Port
• B. Throttle Body
• C. Primary
• D. Manifold

Answer: (C)

The main idea here is to avoid a bottleneck in the path air takes into the engine. The primary runners are the first large-diameter section feeding the cylinder head ports. If the primary is smaller than the head port, it becomes the choke point, limiting how much air can flow into the cylinder and hurting breathing and performance, especially at higher RPMs. Making the primary the same size as the port or slightly larger ensures the flow can enter the head ports smoothly without restriction, while still taking advantage of good velocity for proper fill and mixture. Too large a diameter isn’t ideal, but matching or slightly exceeding the port diameter is a practical balance for efficient airflow from the throttle body into the head. That’s why the primary is the correct choice.