Under Review | From DVS to DDS (and DDJ)

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Under Reviews

FROM DVS TO DDS (AND DDJ)

Carlo Forni

04 April 2016

TYPE
Like most kart engines, the new TM products are two-strokers. Four-stroker engines are still a small niche in karting

125 CC

DISPLACEMENT
125 cc has been the standard for some time now, while in the past it used to be 100 cc

PUSH

START
Push-mode made easy thanks to a decompression valve on the cylinder head that helps the piston

NON-SHIFTER

TRANSMISSION
OK and OKJ name the new clutch-less non-shifter engines that have replaced the KF and KFJ

HOMOLOGATION
CIK-FIA certified at the first OK homologation session in history, valid for 9 years starting in 2016

More than other motorsport companies, Vortex was able to practice on the new breed of engines, thanks to the experience gained in 2015 on the DVS engine dedicated to the ROK Cup non-shifter class.

In 2015, Vortex was the first company to offer a avvia push-start, non-shifter engine with a decompression valve and the removal of the clutch, starter motor and battery, as well as a return to the external water pump (considered the best in terms of reliability and maintenance). The aim of all this was the introduction to the market of the ROK class DVS engine. This experience was the starting point from which the OTK group company began designing the DDS and DDJ engines, which were very different to the KF and KF-Junior, even just in terms of the changes mentioned above, which had become compulsory.
Aesthetically, the differences are clear, with the new engines appearing both simpler and more compact. Regarding performance, the general increase is mainly due to an overall reduction in weight. For the OK, for example, minimum weight goes from 158 Kg to 145 Kg. A lot of that came from increased engine simplicity, which is lighter by about 3.5 Kg and reaches 5 kg if you include the external components, such as wiring and the battery. Furthermore, in contrast to the KF, the OK does not have front brakes, a further saving of about 2 Kg. Of course, there are another 8 Kg to find somewhere… Regarding the OK and the OK-Junior, the former changes most as far as thermal unit and the cylinder are concerned, since the exhaust valve and silencer are now imposed by the regulations, limiting the design freedom that the KF enjoyed.

Both the OK and OK-Junior engines (pictured above, in a comparison with the “old” KFJ, below) are more compact, thanks to the removal of the starter motor, the clutch and the water pump (now fitted externally)

The performance of the new engines mainly improves due to the reduction in weight. The OK class (pictured above, the new DDS engine) weighs a minimum 145 Kg, compared to the KF’s 158 Kg (below, the “old” Vortex RKF)

However, in the case of the OK-Junior, since there is no exhaust valve and the silencer, according to the regulations, was already of only one type on the KFJ, changes to the thermal unit and the cylinder are minimal.
You only have to glance at Vortex engines to note that, as was the case for the KZ, the cylinder is in a vertical position, rather than inclined, in order to optimise the mixture flows through the lateral transfer ports.
Upon disassembling the new Vortex DDS and DDJ engines, you can see how the OTK group company has bucked the trend, persevering with the casting of the cylinder head, consisting of unique piece. There is no machining from solid or the option of disassembling the head, but Vortex claim that there is optimal temperature control. The cylinder ports and transfer ducts have been optimised, while the crankcase incorporates much of the KF/KFJ one inside, except for the reed valve pack inlet.