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test OK VS KZ THE CHALLENGE

TKART Staff

28 April 2016

The karting scene is essentially divided into non-shifters and shifters. There is often a kind of competition between aficionados of the two classes: the former know that they belong to the original philosophy behind karting, i.e. no gears, just brakes and accelerator so that the focus is on the perfect trajectory. The latter, however, add the complexity of gearshifts and achieve the best performance. But is that really the case, especially after the advent of the new OK engines? We went out onto the track with two professional drivers to find out

test in points

Comparing performance and driving styles with the new OK engines and the KZ

Test 1: ok engine with Flavio Camponeschi, official CRG team
Test 2: kz engine with Simo Puhakka, official CRG team

At South Garda Karting in Lonato (Brescia, Italy)

Well looked-after and smooth tarmac, good grip, during the weekend following the 21st Winter Cup. The test was carried out using a CRG chassis and Bridgestone tyres.

15°C

IN THEORY

SET-UP

The kart equipped with the OK engine shall never focus 100% on a set-up with maximum grip, because it will always be necessary to avoid the kart “sticking” to the tarmac too much and thus avoid potential loss of acceleration, especially when exiting bends. Therefore, if on the one hand with the OK it is necessary to maintain a high speed, on the other hand the set-up needs to be light, to reduce the absorption of power by the wheels when they come into contact with the tarmac. The KZ, however, needs to be able to transfer all its torque to the tarmac, so it’s set-up will have greater grip, but it will also “stick” more to the track. However, the latter aspect will not result in heavy losses of time thanks to the impressive thrust of the gears.

TRAJECTORIES

Generally speaking, the trajectories of non-shifter karts are wider than those of KZs. The reason? The karts slide far more and high cornering speeds need to be maintained. The latter are also essential to facilitate exiting bends, moments in which the absence of gears means that the rpm must never be allowed to fall too low, otherwise the slower engine speed would mean that the torque is not sufficient for the kart to exit bends quickly, resulting in heavy losses of time. Obviously, having just the rear braking system reduces the ability to brake of the OK, which by contrast is more effective on the KZ.

OK AND KZ ENGINES

The new OK engines have the advantage of a newfound simplicity of construction compared to the “old” KFs. Indeed, the electric starter, consisting of a battery, starter motor and wiring has been eliminated, as has the clutch and the internal water pump. Consequently, the way the engine works has changed dramatically, especially due to the absence of a clutch and, therefore, the so-called direct drive. Another difference compared with the KF, and the KZ, is the elimination of the front brake. The vehicle loses about 7-8 Kg but, according to the regulations, the minimum weight decreases much more, to 145 Kg, which is some 15 Kg less than the 160 Kg KF. Thanks to these new parameters, the OK’s lap times are remarkably close to those of the KZ.

THE OK ENGINE

47”220

Set-up

Driver	Flavio Camponeschi
Chassis	CRG KT2
Set-up	Standard

The tubes of the chassis used with the OK engine were all 30 mm in diameter; in general, this makes it “stick” less and allows the kart to slide more freely, although it provides less grip.

What we expected

The key aspects are trajectory and braking.
The kart with the OK engine can enter bends so that, if necessary it can sacrifice a little speed going in, in order to maintain a higher speed throughout and exit with high rpm. The kart thus maintains significant torque even during the slowest part of the bend.

Analysis

From the telemetry graph that, based on time, compares the rpm of the OK-engined kart with those of the KZ-engined kart, it is evident that the braking of the former (red line) is less effective. A quick glance shows that the speed curve is less inclined at the braking points. it is clear that the braking system limited to the rear wheels is less effective than the one on the KZ, which also uses front brakes.
Even more interesting is the fact that in almost all bends, the minimum speed of the OK kart is higher than that of the KZ, in line with the objective of maintaining the highest possible speed to exit the bend quickly. In order to do so, entry to the bend is sacrificed and acceleration occurs slightly later than it does on the KZ kart.

Trajectories

The trajectories of the OK were analysed using the telemetry GPS system, together with Google mapping, and then compared to the KZ.
It is clear that the trace of the OK (in fuchsia on the chart) is generally more rounded. This is especially evident in the hairpins (points 1 and 2), where the kart markedly widens its entry trajectory in order to maintain a high speed in mid bend.

THE KZ ENGINE

46’’830

Set-up

Driver	Simo Puhakka
Chassis	CRG Road Rebel
Set-up	Standard

The chassis used with the KZ engine is the Rebel Road and its tubes were all 32 mm in diameter. Therefore, the chassis “stuck” to the tarmac a little more, for greater grip, especially in acceleration, where the KZ’s impressive torque must somehow be tamed and transferred to the track.

What we expected

Gears are a great help, especially when exiting bends, as well as achieving maximum speeds that are higher than those of the OK. It is evident that the key is to enter bends as fast as possible and accelerate just as quickly, while decreases in speed will not be a critical aspect, given that the gearbox means that the rpm can be kept high and torque will remain impressive during acceleration. The trajectories will be sharper, so that there is less distance to cover.

Analysis

The telemetry graph, based on time (horizontal axis), shows how in this case braking is more effective: the yellow line, which refers to the KZ’s speed, is more vertical during deceleration compared to the red line, which is the OK’s curve. Although braking from top speed that were always higher, the KZ took less time to decrease its speed compared to the OK. Speed at mid bend, the slowest point, is lower than the OK’s, but early acceleration follows immediately afterwards, which allows a gain in time.

Trajectories

The KZ focusses on fast cornering and covering less distance: the trajectory (yellow) is clearly sharper when entering bends. Indeed, on the hairpins the kart (the small deviations in the tracking of the trajectories need to be taken into account on the graph) tends to go close to the inside curb at entry (points 1 and 2), which is practically impossible with the OK. On the double inner bend (4), it is quite evident how the trajectory of the KZ, in the second part, is more angled, with greater speed which then decreases in the “V” cusp. On fast bends, especially the one on the main straight, the KZ has a higher speed compared to the OK and tends to be pushed towards the outside, in this case with a wider trajectory.

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