I tried to find more information on the subject but I couldn't. Can you tell me if this change is any good for surf riding?
My own knowledge runs out pretty quickly regarding accelerating airflow, but it seems like a pretty air-restricting factor.
The air mixture reaches the engine faster, but does it reduce power at high revs?
I can't provide a definitive answer regarding this specific manifold without having it in hand. However, the core principle behind optimizing intake velocity is to increase airspeed while maintaining mass flow. In high-performance applications—such as drag racing—intake systems often feature a pronounced taper, typically around a 7-degree included angle. This angle is considered ideal, as it accelerates airflow without sacrificing volume.
The concern that this might reduce top-end power is unfounded. In reality, the primary restriction in most setups is the carburetor. As long as the carb remains the most restrictive component in the system, increasing flow capacity beyond it offers no practical gain.
Many manifolds are designed with an overly large plenum area beneath the carb throat. While this may seem beneficial, it actually reduces airspeed—especially in designs that flare out toward the reed block. In a two-stroke engine, each time the piston rises and the reeds open, air must rapidly accelerate to pass through the reed block. If this has to happen repeatedly during every induction cycle, you're wasting valuable time and limiting crankcase filling efficiency.
It's all about maintaining velocity. Air should be kept moving quickly throughout the entire manifold. The ideal shape is one that functions like a one-way valve: easy for air to move forward, but resistant to reverse flow.
Why is reverse flow resistance important? When the reeds close, the high-speed air column continues moving down the manifold. This momentum helps build pressure in front of the reeds. To capitalize on this, the manifold should discourage any reverse flow. If the shape is too blended or opens outward near the reeds, it allows that pressure to dissipate—ultimately reducing performance.
Pitiful, just pitiful...
