After a great 2010 of testing with our Tony EVR motorized with Rok engine, we decided for a step forward with a Super Rok mounted on a Tony Kart EVRR, the new Tony 2011 chassis, an evolution of the EVR. The Rok Cup kart, as we have already commented, has done a great job in 2010 giving excellent reliability and good performance.
New EVRR chassis
The RACER EVRR, available both for KF and KZ categories, is the refined evolution of the EVR model, which is the chassis that in the last years has allowed Tony Kart to stand out and win the most important CIK-FIA and WSK Series races.
The EVRR is composed by a frame realized with 30 mm diameter tubes. Novelties are solutions such as the lower tank, the new bearing carrier supports that now are one only piece instead of two.
The axle supports are new too, with more holes allowing to adjust the seat in many different ways, which permits quick and fine tuning operations and a big difference in allowing to fix weight balance more easily.
Super Rok increases power and revs
Compared to the Rok engine the Super Rok shows a more developed design with the cylinder head very compactly shaped with the new Vortex design just as for KF1 and KF2 engines. Another immediately visible difference of the Super Rok compared to the Rok is the exhaust valve which can be regulated manually. This surely improves torque curve.
Proceeding along the exhaust side, differences are also in the exhaust system and silencer, which is integrated in the exhaust pipe, more compact and less heavy compared to the one of the Rok, which has the silencer at the end of the exhaust pipe.
Technical data shows maximum revs regulated at 16.700 rpm compared to the 13.800 of the Rok and a maximum power output of 26.5 kW (37 Hp) at 12.500 rpm compared to the 22 kW (30 Hp) at 11.500 rpm. Max torque increasing slightly from 19.6 Nm at 10.000 rpm to 20.2 Nm at 11.500 rpm. Still the higher maximum revs will permit to use shorter transmission ratios (bigger rear sprocket or smaller front sprocket) and so have much better acceleration.
Weight of the engine is 15 kg, excluding the exhaust system, just as the Rok.
Shifting to the internal part of the engine the Super Rok has a 30 mm high reed valve passage (for each reed petal), compared to the 27 mm of the Rok, for a total height of the Super Rok reed block of 72 mm compared to 65.5 mm of the Rok. Also the length of the openings of the reed valves changes from 20 mm in the Super Rok to 17 mm in the Rok reed block.
While conrod length, bore and stroke are almost equal between the two engines, it is clear that the different maximum revs, and different torque and power curves, ask for different opening and closing of exhaust and transfer ports. The exhaust port will open earlier (194¡ duration) on the Super Rok to help performance at higher revs, vice versa with the Rok (184¡ degrees duration for exhaust). For similar reasons the Super Rok cylinder has 5 ducts and ports transfer system, while the Rok has three, with a bigger TT central transfer duct.
As said the conrods are identical and so are the pistons and the crankshafts in the two engines. Small differences in the crankcase. The carburettor is a DellOrto VHSH 30 in both cases. Ignition systems vary for max revs limitation, but are both variable.
First sensations on track
Once looked at the data of the Super Rok versus the Rok enthusiasm increased in me going to the Lonato track to collect and test the new creature. We arrived Saturday morning in a very cold day at the track near Brescia, cold but no rain and that was the first important aspect for our test day! Most importantly we were on the track where all the main Italian kart companies do most of their testing.
Kart was ready with Bridgestone tyres used for the Rok and Super Rok categories. We just set tyres at 0.55 bar and as always just filled the tank with fuel-lubricating oil at 6% and greased the chain. Water in the radiator and cooling system, connected the battery for the starter and I was ready to go. Some few laps just for a quick review of the track and feeling was immediately great. Especially exiting curves acceleration was strong, with more push compared to the Rok engine and no problem in the very first acceleration, which was somehow present in the Rok. This was mostly dew to the high ratios the Rok needs because of the strong limit to maximum revs.
After the first laps I started pushing strong also along the main straight and I felt all the power of the engine and all the great acceleration at all revs of the curve. And this was maybe one thing that you miss with the Rok, the sound at high revs! Still it is not the sound of a 100cc direct drive engine, which also gives a more immediate push just in the few instants when pressing on the accelerator, this also dew to no clutch present.. But finally Super Rok shows great performance and, most probably, this will be combined with the excellent reliability of the Rok family. This we will start testing in the next months.
Chassis also showed great balance as we experienced with the EVR, but more detailed sensations and behaviour of the chassis will be done with fine tuning of the different parameters of chassis setup.
A whole day at the track with absolutely no problem at all and, as usual, no real need to touch carburetion to have a great test of almost 80 laps!