Tech Talk: Kart engine tuning – Part 1

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One of the most interesting and mysterious topics in the kart World is engine tuning. Two stroke-engines are so simple yet have so many parameters to tune and optimize. Performance can change from engine to engine, and from a simple new engine to a tuned one. What is true though is that engine tuning, done of course by keeping engine parameters within values given by technical rules, can give some additional horse power, increase torque, but this will result in 2 to 3 tenth of a second lower lap times. Halves of a second or even greater lap time reduction cannot be determined by the simple tuning of an engine, but is the sum of some other additional parameters like driving capacities and chassis setup (including tire performance).

What kind of tuning?
What is engine tuning, what is there to modify? Well one important aspect is that kart engines, especially the latest homologated ones, have already great performances and are tuned by the engine manufacturer. Finer tuning can be done by the engine tuner, but must be extremely precise in order not do spoil engine performance. Working on different parameters and elements of the engine without the right knowledge of engine functioning and possible tuning tips can only bring to a reduction of performance of the engine. Such reduction will easily be greater then the increase in performance we can generate with the right tuning.
The possible actions on the engine can be focused on some main aspects:

1. Acting on engine geometrical parameters such as: tolerances between piston and cylinder, piston ring gap measurement, phasing, squish height, compression ratio. These parameters can be regulated as indicated by the engine builder to have precise settings and good performance or they can be varied to increase performance (if one knows how to vary them correctly). Most of these parameters will also have to be checked each time a piston is changed or the cylinder is honed, so you will have to learn to deal well with all the phases of basic tuning.

2. Varying some engine components to permit best performance (spark plugs, reed valves, lubricating oil). These elements permit better performance and sometimes also better reliability of the engine.

3. Acting on shapes of the engine as ducts and ports. This action determines irreversible changes to the engine and must be done with extreme care, even more than with all the other tuning actions. Any mistake will damage the engine definitely.

4. Tuning external parameters like exhaust pipe length, transmission ratio, carburetor. The regulation of such parameters is not usually considered tuning, but their importance is so high that really an engine can express all its potential only if all the parameters, these ones included, are perfectly tuned. Also these parameters must be adjusted for example every time we go on a different track. In particular carburetion regulation must be controlled every time we change track, or weather changes, or the weight of the driver changes. Carburetion is probably the main parameter to regulate that sensibly effects both engine performance and reliability.

First step
Since competition kart engines are built to produce extremely high performance, they already are very close to maximum power output as they are when sold by the constructor. Mass production can though generate some small misalignments of geometrical parameters of the engine. The first step is then to measure all the main quotes of the engine. Squish height, piston and cylinder tolerance, phasing (opening and closing of exhaust, inlet and transfer ports), compression ratio and combustion chamber volume.

All engine builders homologate their engine (following the rules of FIA) indicating the basic parameters. These homologation data is present on “Homologation fiches”. The indications on the Homologation fiches are a base from which to start verifying the above indicated parameters. A more precise indication of the values of the engine parameters can be obtained directly by the engine builder or by the dealer that has sold you the engine.

Instruments for parameters check
To examine and measure all the parameters of the engine listed in the first step of engine tuning we have to be equipped with a caliper, a Palmer caliper, a graduated wheel (for measuring of crank-shaft rotation), a comparator for cylinder diameter measurement, thickness measurement plates, a graduated pipe for combustion chamber volume measurement. So find the parameters that are the right ones for your engine and next issue we will start with the first phases of tuning taking each single parameter at the time.