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TKART magazine Under Review | The KZ 2016 by Modena Engines
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18 January 2016
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2-stroke engine, like the vast majority of kart engines. 4-stroke is a small niche

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125 CC

125 cc has become the standard displacement. 100 cc engines are a thing of the past.

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Starting is the same as always, the push start, with the clutch being released by hand in second gear.

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Two “large families” of engines for karts: single speed and gears. The KZ is a 6-speed unit.

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The approval is for the KZ with gears, valid for 9 years starting from 2016.

Under the guidance of R&D manager, engineer Roland Holzner, Modena Engines, a company that recently entered into karting but has already scored some notable victories, supported by a group such as ASPA, revamps its offering thanks to the approval of the new KZ engine: 2016 MKZ

The KZ category has changed little over the years, providing regulatory stability and performance. However, thanks to the flair of its designer, engineer and R&D manager Roland Holzner, Modena Engines has mixed things up a little by introducing several innovations, albeit in a controlled manner to avoid unnecessary risks. In addition, following complaints concerning some of the technical solutions used on the previous approval (initially approved by the CIK, then challenged on some aspects), Modena Engines has attempted to steer clear of all possible disputes.

Fluid dynamics is at the base of the new MKZ’s improvements, starting with the intake of air and then mixture into the carburetor and the reed valve pack, through to the crankcase. A new height and tilt of the reed valve pack has been set, widening the angle between the valve pack and the cylinder to the extent that the Schnuerle portings can be seen from the reed valve pack. In so doing, the intake flow uses a straighter, and therefore more efficient, path to reach them.

Among the more innovative aspects is the V-Flow reed valve pack that, compared to the traditional type, avoids the impact of the mixture flow with the lower part of the piston and directs the flows directly towards the Schnuerle portings.
Holzner, the designer, has shortened the intake duct, so the air doesn’t heat up upon contact with the walls of the duct and the frequency of the incoming pressure waves is improved
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To improve thermal transmission the exhaust duct has been shortened and the first section of the silencer has been lengthened, with both being connected directly to the cylinder with an O-ring instead of a gasket
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The “scarf” is a sort of shell covering the cylinder. It is designed to prevent excessive cooling of the cylinder when air hits it with the kart in motion, especially in winter
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The flow sections have been increased and the final profile reed valve seats is wing-shaped to stop the flow line from detaching, which in turn would cause turbulence and reduce the section through which the mixture flows. The disputed plastic insert located in the intake duct on the previous approval has been eliminated and the duct itself has been shortened in order to keep the air temperature down, allowing more into the crankcase and the combustion chamber (cool air is denser, which is to say more concentrated).
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