Which intake manifold design provides the lowest restriction from the intake manifold to the cylinder head?

• A. Single-plane intake
• B. Tunnel ram
• C. Plenum manifold
• D. Dual-plane manifold

Answer: (B)

The tendency of air to flow with the least resistance is boosted by short, smooth, large-diameter runners that connect directly to the cylinder head ports. A tunnel-ram intake is built with very short, straight runners and a wide plenum, feeding each port with minimal turns and friction. That design minimizes pressure drops and velocity losses as air moves from the intake to the valve seats, especially at high rpm when flow demands are greatest.

Other designs trade off high-end flow for different operating ranges: longer or more curved runners and different plenum arrangements in dual-plane and other manifolds improve low- to mid-range torque but introduce more resistance at high rpm. A plenum-only design can also add path length and potential turbulence, which tends to raise restriction compared with the tunnel-ram setup.

So the tunnel-ram design provides the lowest restriction from the intake manifold to the cylinder head.