THE EXHAUST - ADJUSTMENTS

TKART Staff

15 October 2016

In the previous article “The exhaust - how it works”, we saw how much the exhaust is critical to the timing of a 2-stroke engine. Now, we will be analysing how the adjustment of its length can optimise the phases regarding the “suction” of the burnt gases and “slowing down” the expulsion of the mixture from the combustion chamber

WHAT IS IT?

HOW DOES IT WORK?

IN PRACTICE

As analysed in the TKart article that you will find, again in the “Tech Talk” channel, immediately prior to this, in racing kart’s exhausts optimise the washing and discharge phases of the 2-stroke engine cycle by “sucking” the flue gas from the combustion chamber, due to the negative pressure waves generated by the cone, and “slowing down” the discharge of the fresh mixture from the combustion chamber, due to the positive pressure waves generated by the contracone. These two phenomena can in turn be optimised by adjusting the overall length of the exhaust.
At the time of 100 cc engines, the length

adjusting operation was rather simple, using flexible conduits cut into different lengths and positioned between the bend in the hose and the exhaust. A solution which is still used to adjust engines such as the IAME X30.
Other engines such as the TAG, or like the new OK, adjust the length of the exhaust through the plate mounted on the exhaust and approved in different thicknesses. It must be added, however, that with the advent of the exhaust valve (absent in the 100 cc engines), the exhaust phase is also very much based on this component.

ADJUSTING THE LENGTH OF THE EXHAUST MOVES THE TORQUE CURVE TO HIGH ROTATIONS IF THE LENGTH IS REDUCED; OR LOW ROTATIONS IF IT IS INCREASED

WHAT IS IT?

HOW DOES IT WORK?

IN PRACTICE

EXHAUST

LONGER INITIAL PART

MORE ANGLED CONE AND CONTRACONE

INCREASED LENGTH BETWEEN THE TWO CONES

The variation of the length of the exhaust, as mentioned, results in significant differences in the combustion chamber washing process by affecting the ability to eliminate the flue gases and mitigate, as far as possible, the discharge of fresh mixture. Evidently, any adjustment is more or less appropriate in relation to a given number of revolutions.