Before building a racing engine for a go-kart there are a few determinations that must be made. For one will the engine be used on a kart that’s competing in Sprint races that involve turning left and right or in Oval races where karts turn left only. This is necessary in deciding on the horsepower of the engine, since getting in and out of corners and back up to speed quickly requires more horsepower. With Oval racing it’s more a matter of the gearing because once up to speed the demand for horsepower is greatly reduced.
Another determination is the size of the engine to be built, since go-kart competitions feature different classes which are based primarily on the engine displacement. Once these determinations have been made the process of building the engine boils down to two alternatives.
The first is to completely assemble a new engine from a set of parts or engine kit that can be purchased through a dealer or even through reputable online sources. Certainly building a racing go kart engine this way has certain cost considerations and time constraints because new engines are pricey and it takes time to assemble them correctly. In addition there’s testing and adjustments to any racing engine so this manner of engine building is likely more in keeping with a full-blown professional racing effort.
The second alternative is converting an already assembled engine to work on a racing go-kart. Here the resources for engines are quite vast and one can find just about any size engine from 150cc to 350cc and up along with numerous ranges of horsepower from 5 hp to 30hp and up.
Some still entertain the idea of pulling an engine from a power mower and bolting it to a go-kart frame. But the problem here is that a lawnmower engine has a vertical drive system and a racecar has a horizontal drive system. The conversion can be accomplished but it is involved and would likely end up costing more than purchasing a horizontal drive engine and rebuilding it to suit the specifications of a certain competition class.
Again the sources for small engines are numerous and finding an engine that’s close to the horsepower and displacement that’s desired is relatively easy to do. There are schematics and spec books on engines of all sizes and changing the bore and stroke on one of these engines out to accommodate a competition class is not a difficult endeavor.
By pulling the cylinder head and removing the crank case pan one has access to the crankshaft and combustion chamber. The valves can be removed and polished and the cylinder sleeves changed out from aluminum to steel. New pistons, crank bearings and valve guides can be installed and this will add durability and longevity to the racing engine. And be sure to implement an exhaust system with minimum bends to minimize back pressure and increase the efficiency of the engine.