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Tkart magazine

Under Review | Vortex RSZ e RTZ, the evolution of the World Champion KZ engine

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01 March 2019


Like most kart engines on the market, the RKZ is a 2-S. 4-stroke engines are still a small niche

125 cc

125 cc. Is now the standard cylinder capacity. 100 engines are a thing of the past.


Push-mode as in all KZ engines, with hand-release clutch and neutral to 2nd gear shifting


The RKZ belongs to the gearbox “family” of karting engines.
It has a 6 gear manual transmission


It is the shifter KZ, valid from 2019 to 2021.


Improving a World Champion engine is never an easy task. Perhaps, this is also why for the Vortex technicians, when it came time to present the new evolution of the RKZ (KZ World Champion and winner of the CIK-FIA KZ2 Super Cup in 2018), decided to…double, by homologating  the RSZ and RTZ models.

Provocations aside, the choice of the OTK Group engine manufacturer has been well thought out and the difference between the two engines focuses almost exclusively on the length of the connecting rod: 110 mm for the RSZ and 115 mm for the RTZ.

Generally, a long connecting rod provides increased smoothness at higher RPMs, while shortening it, increased torque is guaranteed with the engine at lower RPMs. Departing from this concept, with the Vortex RSZ the Group tried to optimize the engine for its use on mixed design circuits, normally on medium – shorter length shorter straight stretches; conversely, the RTZ is more functional on faster circuits.

Remembering when the RKZ model was revolutionary compared to the previous Vortex engines, for the RSZ and the RTZ is more accurate to talk about evolution. On the new engines, in fact, all the choices that were made for the RKZ are verified, starting from the free air cooling of the crankcase. The flow of air enters in the opening that is positioned in the front, under the carburetor and through a conduit, to then flow back up around the turning crank mechanism and the gear housing.

The forced air cooling system allows to maintain a more stable temperature when compared to a water cooling system, subject to variations within the cooling circuit depending on the type of track taken on. A more constant temperature is quite useful to achieve a stable carburation which allows to optimize the engine’s performance.
“Evolution”, however, does not mean that innovations are not present.  Let’s start from the head, which is always dismountable and is not offered in a single piece in aluminum alloy, the standard solution for the RKZ. The variation is dictated by the change in the regulation which does not allow any longer the homologation of any variants. The fact that it is dismountable, is an advantage both for clients and trainers, who can inspect the head without having to completely replace it.

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