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Tkart magazine

Special | Guide to power test benches for kart engines

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15 March 2022

It is a great ally of all trainers, an adrenaline-pumping playmate of the lucky “addicted to engines” people who own one. Many talk about it even if few know about it in detail. Let’s therefore get to know this important work tool better and in depth

What it is, what it is used for and the types

There are different types of test benches (with relative strengths and weaknesses) and the discussion about which is the best is often the subject of heated “bar” debates among fans.

The engine test bench, also called the “brake” in the jargon of experts, is a measuring instrument designed to measure the mechanical characteristics (mainly power and torque at different operating speeds) of an engine connected to it. The operating principle is quite elementary: In fact, to measure “the power” of an engine, it is literally braked in its rotation by the test bench which consequently gives its performance values. Based on the type of resistant torque used and whether or not it is modular, we can divide power test benches into two types:
– inertial (also referred to as “static”)
– dynamometric (also referred to as “braked”)
The former is composed of a mass of considerable size and weight, useful for creating a certain inertia and applying a resistant torque.
The latter, on the other hand, uses (combined with a mass of limited size and weight) an eddy current brake which generates very precise tests. Furthermore, if the software that manages the system allows it, it also introduces the possibility of faithfully reproducing a well-determined use (example: the operation of the engine as used on a lap of a given circuit) thanks to an increase or reduction in intervention of the eddy current brake.
This classification is independent of the shape of the bench or whether it can host a specific medium that you wish to test in one way rather than another.

What it is composed of

Above, a diagram of an inertial bench. Below that of a dynamometer.

In the case of an inertial test bench, the mass and therefore the very high inertia of a large roller is exploited so that the engine or vehicle to be tested must try to move through a mechanical connection or with its own wheels resting directly on it.
With these kinds of instruments, the inertia cannot be adjusted and therefore remains the same in all tests, regardless of the type of vehicle being tested on the bench.
The vehicle being tested gives a certain acceleration to the roller without activating mechanical or magnetic brakes since, apart from the safety brake, they are not present.
It is a very quick test and we are aware of the fact that it does not allow checking the engine curve accurately, since the large inertia of the roller hides or even amplifies uncertainties or performance gaps.
Above all, the inertial characteristic of each test bench precludes certain uses or at least makes them less suitable. In fact, one can simply imagine that a very high inertial test bench cannot accommodate a low power engine, just as, on the contrary, low inertia brakes would be useless for very high powers. The mass must therefore be adequate according to the engine power range and must allow the acceleration times of the engine to be aligned with those found in real use on a track.

The inertial type

An example of a hand-made inertial power test bench.
© Minimoto VR Forum

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