Karting Engines
Overview
Karting typically uses two different types of engines. These are two cycle and four cycle engines. In sprint karting two cycle engines populate the majority of classes, however, there is a population of highly dedicated four cycle sprint racers. More recently an influx of extremely high performance four cycles has been introduced, this has subsequently encouraged many two cycle based racers to switch. In oval karting, four cycles are the primary source of forward drive. However, a small percentage of dirt oval participants are running two cycle power plants. Meanwhile, road racing experiences a mix of four cycle and two cycle power plants. Lastly, there remains a few small interests in rotary type power plants, but these types of engines have not yet seen large amount of activity.
The Two Cycle
Two cycles engines are characterized by a few distinct features. They first gained popularity in karting because of their uniquely simple design. Two cycle engines have relatively few parts and can be known for both power and reliability. One of the main characteristic of a two cycle is the lack of isolated crank case. A two cycle engine does not isolate the the combustion chamber and induction system directly from the crank case and because of that does not hold any oil. Two cycle engines use a premix gas/oil combination. The oil content serves to lubricate engine internals and the gas is efficiently burnt in the upper cylinder.
Some two two cycle engines are designed around reliabilty with a slightly de-tuned sense of performance, while others can reach an RPM reading of over 19,000. These engines are not known for being environmentally friendly, and as a result are feeling some pressure from the more cleanly four cycle engine.
Types of Two Cycle Engines Used in Karting
Piston Port
Piston port engines are the simplest of the two cycle engine. Piston port engines use only the piston to control both the induction of a fuel rich atmospheric content and the exporting of burnt fuel tot he exhaust.
The Yamaha KT 100, and HPV engines are very popular examples of piston port engines currently used in karting competition.
Reed Valve
Reed valve engines work very similar to piston port engines, however, the piston does not control both induction and exhaust. Reed valves, which are typically small carbon fiber or steel pedal like devices acting as a one way check valve. This check valve action allows for a more optimized exhaust port timing, ultimately generating more power. Thanks to the simplicity of the reed valve assembly these engines have gained much popularity in karting.
Reed valve engines are used in the ICC, ICA, Moto based shifter, and many TAG engines.
Rotary Valve
Rotary valve two cycles take advantage of their ability to have very precise intake timing. The power characteristics of these engines can be tuned using the rotary valve to provide many different delivery curves. While these engines can provide allot of power, they have fallen out favor in karting.
Detailed Description of A Two Cycle Engine Running
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The Four Cycle
Four cycle engines are characterized by a few features of their own. First, four cycles gained popularity due to there low cost and relatively simple nature. These engines originated from lawn mowers and were easily adaptable to a kart. Typically, these engines do not produce the same amount of power as a two cycle, however, they can be as or more reliable. More recently, a switch to a slightly more modern four cycle engine has occurred. This has lead to a slight increase in both power and reliability. These engines use a sealed crankcase and as a result tend to be much more environmentally friendly.
Currently, there is a strong surge in population of extremely high performance four cycle engines. These engines are designed to replace their two cycle cousins, consequently, they produce an extremely high amount of power, and are more environmentally friendly than their two cycle counterpart.
Detailed Description of A Four Cycle Engine Running
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But Wait, There's More
Shifter Engines
Shifter karts utilize an engine and transmission that enables the kart pilot to shift. These karts can be extremely fast and are recommended for very experienced drivers and mechanics only. Shifter kart engines typically are 125cc and have a 5 or 6 speed gear box. Two types of shifter kart engine exist. First, is the Moto based engine. These engines originated from motorcross bikes hence the "Moto" designation. Second are the european or "Inter-continental C" engines. These engines are specific made karting engines. Both Moto and ICC engines have gearbox's that are and integral part of the engine, hence their inclusion in the Engines section of Karting101.com.
Like mentioned above, two cycle engines are slowly becoming a way of the past. This is still true in shifter engines. Motorcross is quickly becoming four cycle only and because of that move some people have begun experimenting with Moto based four cycle shifters.