Which configuration improves airflow, but may cause unequal fuel distribution?

• A. Single-plane
• B. Hybrid-plane
• C. Dual-plane
• D. Multi-plane

Answer: (A)

In intake manifold design, transferring air into the cylinders involves a balance between flow and how evenly that air—and the fuel attached to it—reaches each cylinder. A single-plane configuration uses a single shared plenum feeding all runners, which reduces restrictions and allows air to flow more freely at higher engine speeds. That boost in unrestricted air helps increase top-end airflow and horsepower when the engine is turning fast. The drawback is that, without separate plenums or tuned runner lengths, the air distribution to each cylinder can become less uniform at lower to mid RPMs, making fuel distribution less even and potentially causing some cylinders to run richer or leaner than others. This is why single-plane manifolds are favored for peak high-rpm performance, while designs with separate plenums and tuned runners (like dual-plane) excel at low- to mid-range torque and more even fuel distribution.