Ask The Editors: Stacks of Velocity?
The mysterious stack.
That’s a solid question. You don’t hear a whole lot about them these days and it gets even more confusing because they are often called things like “horn cup funnels” or “air horn intakes”.
The velocity stack is just the funnel shaped plastic cone (sometimes aluminum) that connects the airbox to the carburetor. Occasionally you’ll see what appears to be an air filter jutting out from the carb into the open air – this filter is likely there to separate airborne particulates before they can enter the velocity stack.
So what is it, you ask? It’s just an intake of decreasing diameter as it approaches the carb. Why? Because as you cut off space, the air traveling through said space is forced to accelerate. This is why the nozzle on your hose is narrower than the hose itself.
By making the air speed up as it enters the engine, you are gaining a slight power advantage that is known collectively as force air induction (turbo and superchargers take this concept to the next level by incorporating a fan-driven compressor to make this happen).
In short it’s a simple little physics hack to gain more power without any complex or moving parts.
