Reclaiming Drive

Columns: Track Test
We tested the karts for the OK and KZ2 classes driven by Basz and Hajek in Kosmic colours, great help given by OIP telemetry. this is what we noticed in the differences between the direct drive and gear class.

We just couldn’t refuse this occasion, nor could we minimise it, so when the OTK group gave us a chance to try, immediately after the Winter Cup, the official Kosmic-Vortex karts that had raced driven by Karol Basz and Patrik Hajek, we did more than just do a few laps. A chance of lapping with the help of the most winning team spurred us to try and get more out of this test, and our friends from Officine in Progress came along to help us, they filled the kart with sensors, connector and data acquisition blocks. Often under watchful eyes, at times playful and at times a little bit worried, but at the same time interested, not only of the two mechanics who helped marvellously with all the operations (Alessandro Fracasso and Thomas Mardaga) but of also others who were working under one of the best tents in the world karting circus. However still appreciating the skill of assistant mechanics, the support of the official drivers, with whom we worked to take these karts to the limit, is priceless. Also because, obviously, besides being professionals they know their “work instruments” inside out and in any case, at a level that people like the person writing and the other test driver, Daniele Parravano, could ever dream of reaching. On the other hand, it is up to us to describe those sensations that skilled “regular” drivers have long metabolised to be able to explain properly. And the fact that after the test we all practically agreed on everything only confirms this. Let’s take a closer look at what we got emotionally and technically from these two karts.

Actual Original Karting
Starting from Basz’ kart number 209, we can but confirm that drive of the OK kart is something that reconciles you with karting in general. It’s reactive, with a firm character and without too many uncertainties. A small beast that has to be tamed without the danger of necessarily finding yourself mangled. And yet there have been lots of small things that have made something that, even just by watching these karts lapping you get a very good impression. It all mainly concerns weight, it is lighter, but also for who like me was 10kg over minimum weight allowed by regulations, and things weren’t at all depressing, on the contrary. There is also a limiting device set at 16 thousand revs to help us too, and this allows for better ratios without being condemned to suffering ignition cuts, that we did however feel it just before entering the “big turn”. We must underline that ratio on our kart was that used during the race, so there were no “discounts” at all: the lads from the Brescian team aren’t that type... So with exciting acceleration, we got a taste of the kart’s excellent response round turns. Here in fact, the engine, which although “set up for racing without any compromise”, is always reactive and in torque between one turn and another, without any drop. Obviously you have to take great care as you drive along so as not to go below a certain value. However, this we find to be positive, meaning that we go back to find that, what makes the difference is managing to “find” those 100 revs more round the turn, without being hopelessly under-torque “always & however” like it used to be
with the KF. To be clearer, round the last turn in Lonato we found that the engine was already in torque well before reaching the external curb – this was so even when the turn in question wasn’t tackled in the best of ways, otherwise you have everything already when you “open” – while the engines from the previous generation gave “signs of life” also only when you were at the end of the external curb. We got the impression that delivery is distributed much better over the revs, and it is good that this result has been reached apparently without any important changes.
You must be phisically fit
Thanks to this engine response, it is also much easier to find the limit for chassis response too. As usual for chassis made in Prevalle, among which Kosmic is one of the main brands, physically speaking you have to have excellent steering wheel control. Doing this, when you are physically fit, forecarriage response is guaranteed; also because you have the right evaluation for tackling turns neither too fast nor to slow. We all know the reason for not arriving too fast; rather, talking of “too slow”, the thing is arriving with sufficient speed you can allow the kart to work as it likes, that is loading forecarriage well to give the right direction on corner entry (and hence increase exponential speed on corner entry) and lifting internal left wheel properly. This way you also get improved ground rest and stability when you accelerate again, the chassis is released so as to give a progressive glide on exit. If, instead there has been some hesitation, it’s easier not to get enough wheel lift, or it comes down too soon, ruining set up and the kart starts jumping. The overall candour of the kart does so, however, it allows you to “start off” well and get better and better as you lap. To give you a specific example, it’s the same kart that makes you feel how, at the part of the track after the first turn when you go onto the old track, there is no need to brake too soon and it’s better to enter the turn with as much speed as possible, for you “to rest” well on forecarriage in release and join the two turns that take you to the downhill part.

Wicked braking
Talking about the chassis, Kajek’s kart number 117, the basic chassis response doesn’t alter, although we are talking of two distinct classes, seeing that
in this case it’s the DZ2 class with gears. What you feel immediately just one rear disc to a system that works on all four wheels, but the usual power of the OTK brakes is something that at first, always takes you a bit by surprise that you have to remember to support yourself resting quite a bit on the steering wheel when you brake. In any case they are quite modular during the turn entry phase. Davide who felt less at ease with some of the delivery characteristics of the powerful Vortex RKZ also found this response exciting. On one hand it’s evident that set up to the limit bring about more power, but also a more restricted area of use, that only the best drivers in the world manage to make the most of this power. In fact, luckily there are gears, because in this case each time there was a hesitation the engine stalls and it wouldn’t pick up
again if we couldn’t drop a few ratios. This is quite
a difference compared to the response of its “little brother” for the OK class.
Nevertheless, in this specific case, we even found that to make everything even more “explosive” was the sudden delivery, when we opened throttle, was a minor problem concerning carburetion. An effect that probably official drivers manage
to overcome thanks to their aggressive use of the acceleration pedal like “full down immediately”,
but that requires a rather cantankerous drive style when tackling turns. And this also reflects on chassis behaviour along the straights. Furthermore, at higher speed you notice, besides so much thrust also a tendency to “stall” once you have gone
over the power peak that you have to change gear promptly without any hesitation. Obviously we are all well aware that “professional” engines make things more difficult for amateur drivers, but it’s always hard to run into this “technical truth”. But it’s also exciting...

OTK as it should be
Vortex and Kosmic are two well known brands that depend
on the OTK group, with separate manufacturing sites: everyone knows that the chassis are made in Prevalle, near Brescia, while the engines are made near Pavia, now at the
new factory in Campospinoso. Among the characteristics of the Vortex DDS for OK classes – available also in versions for the Junior DDJ without a valve on the exhaust – there is an aluminium cylinder with five transfers (instead the exhaust is oval with two boosters) with cast iron barrel machined on a numerically controlled machines. According to regulations it has reed induction (in this case with horizontal reed pack) and bore/stroke ratio is “square” (54.00x54.29 mm); there’s the balancing countershaft in the base and there is the housing
for a water pump if needed, which is usually left externally though. Cylinder and cylinder head are very similar, at least theoretically, for the Vortex 125 RKZ with gears: compared to the DDS, looking you only notice that the valves are missing, from the one on the exhaust to the decompressor valve that characterises the OK direct drive engines. However the barrel isn’t made of cast iron but with a Nicasil insert. In this case in the besides, obviously the gearbox in the base there’s a reed pack that goes better with the 30mm Dell’Orto carburettor. While the driving shaft offers 54.45 mm stroke and it is connected to a 115 wheel base connecting rod made from a solid.

Created by: - 17/03/16

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