Roughness of kart engines pipes, why it's so important

THE ROUGHNESS OF THE PIPES

TKART Staff

24 April 2017

A question that is often asked is: “How come the overflow and exhaust pipes are rough and not simply polished?” The answer has to do with the “boundary layer” phenomenon, a very controversial and important aspect in the development of 2T racing engines

WHAT IS IT?

HOW DOES IT WORK?

IN PRACTICE

Sometimes, less experienced tuners work on the engine of their karts as follows: they take a fine grain cutter and polish the various pipes thoroughly, convinced that this makes it easier for the air-fuel mixture to pass through them and, therefore, increasing both the filling of the combustion chamber with fresh mixture, and the emptying of the combustion chamber of the combustible gases. This is all wrong!
Why this is so can be gleamed by observing nature: why, for example, is shark skin slightly rough and not completely smooth? Or, passing from nature to work performed by mankind: why are the hulls of America’s Cup offshore boats and catamarans, as well as military submarines, also rough and not flat and thoroughly polished?

The answer comes from the laws of fluid dynamics, capable of scientifically coding what has been discovered through observation over time, that is, that in some situations friction diminishes if a fluid comes into contact with a slightly rough surface rather than a completely smooth one.

Someone in the motorsport field might argue, however, that Formula 1 cars have very smooth and polished surfaces (for reasons regarding aesthetics and sponsors ...), but, as we shall see, this is a very different situation from that of a 2T racing engine pipe.
Whatever the examples or situations, however, in the end all these discussions are tied to one single phenomenon: that of the “boundary layer”.

THE BOUNDARY LAYER ACTS AS A LUBRICANT FOR LAMINAR FLOW FLUID, BUT ALSO REDUCES THE PASSAGE SECTION

Shark skin

Although apparently smooth, shark skin is, in fact, formed by a series of collagen micro-dentures that allow the fish to have more efficiency and speed when swimming. The principle of its operation is the same as that applied to the 2T engine pipes to facilitate the flow of fluids

WHAT IS IT?

HOW DOES IT WORK?

IN PRACTICE

BOUNDARY LAYER

OVERFLOW

PIPE MIXING

Fluid dynamics requires any fluid (liquid or gas) that passes through a pipe or comes into contact with a surface to create a “boundary layer”. That is, it forms a thin layer that, instead of running parallel to the pipe’s walls (laminar pattern) has a turbulent motion generated by microscopic vortices that rotate on themselves. This layer functions as a kind of lubricant for the rest of the fluid, which flows over it virtually without any friction, maintaining its laminar pattern.