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Driving report KTM 400/520 EXC Racing
Take it easy
Less can also be more. With the new, feather-light four-stroke sports enduro, KTM immediately landed a world championship title. The production version will hardly differ from the World Cup racer.
Title and runner-up world championship in the 400 four-stroke class, plus second place in the large four-stroke engines over 500 cc – the debut of the new KTM sports enduro bikes could hardly have been better this season. But resting on your laurels is nothing. At least not this Monday after the World Cup final in the north of the Czech Republic.
Press event. But forget the motto: We drive the glorious world championship machines of the factory drivers. For the first year there is no two-class society at KTM. From the slopes to the box, the factory machine is a serial racer, is the motto. Material testing because it has to be. Because time is of the essence. In December, the first of the planned 3200 series machines should be available from dealers. Almost exactly two years after Yamaha (see box on page 171) threw gauntlet down to all off-road forges with the four-stroke crosser YZ 400 F and the Enduro WR 400 F.
The bar is high – and, at least on the construction plans, is easily skipped by the KTM new creation. The new engine weighs 28.5 kilograms – one kilogram less than the Yamaha unit. And yet everything is there. Six-speed gearbox, two oil filters that keep the scarce amount of oil of just a single liter (Yamaha: 2.5 liters) meticulously clean, vibration-reducing balance shaft and electric starter. Implanted in the almost unchanged chassis of the in-house two-stroke off-road line, the complete enduro only weighs 112 kilograms according to KTM. The Crosser is said to weigh only 105 kilos.
The first contact with the 400 impresses. EXC Racing is graceful. Not even the voluminous silencer required for four-stroke bikes disturbs the slim line that is familiar from two-stroke bikes. The standard electric starter is even more impressive. The pressure on the button lets even the most hardened mud knights degenerate gratefully into stollen soft eggs. The special test on the meadow attracts with handy residents, sleek driveways and descents and tricky, extremely tight turns.
The first acceleration already confirms: The uncomfortable hardening of the rear wheel suspension, familiar from all two-stroke and large four-stroke vehicles, does not occur. Without being wedged out, the EXC 400 thunders over the bumpy slope with full traction even under full load. Admittedly, the suspension coordination of Sala and Co. is – helpful for this discipline – clearly on the soft side. Its mite also contributes to the characteristics of the 400 propellant. The little four-stroke engine revs up like an electric motor. No sudden hard onset, no unexpected drop in performance. The more speed, the more power. 44 HP, almost as much as the WR 400 in sports trim, should and should be. However, the KTM drivetrain is missing a bit for the extreme revving of the Yamaha unit. Maybe it’s because the KTM’s stroke is four millimeters longer than that of the Yamaha. If you want to move forward, you have to stir the six-speed gearbox a little more often. As a consolation: with or without the hydraulically actuated clutch, the gears slip in without any problems.
But the handling is impressive. As the concept promises, the sports guy can be rocked through corners as nimble as a two-stroke. You only have to be careful when the bend is very narrow and the speed is too low. A brief bump and the engine dies. A concession to the four-stroke engine’s ease of starting, which is kept at a top level by means of a lean carburetor set-up. Simple remedy: more idle, even if the said electric starter can spread the cloak of forgetting about the clumsiness in a flash.
Switch to the 520. Periphery? Everything as usual. Only duller and more sonorous in the sound. And when driving? 510 cubic centimeters. Nobody needs more. Just enough to generate full propulsion from the hairpin bends. And not so much so as not to be knocked about by a kicking hindquarters. The engine revs up cleanly and quickly. No chopping or chain whipping at low engine speeds, acceptable revving and, when flying for longer periods of time, not the compulsory thrust of gas to prevent the stew from dying off, as is the case with very large four-stroke engines. He only does that in very tight turns – slap, and out. The reason and the antidote are known.
Hat’s KTM with the two newcomers now managed to raise the bar even higher in the off-road four-stroke segment? In terms of handling, this is obvious due to the weight advantage of at least eight kilos. When it comes to the engine, the 520 inspires more than the 400 upon first contact. The next comparison test among the respective displacement colleagues will make it clear.
400 cm³: the new trend
The plan was good: In 1997, Yamaha started a 400 cc crosser to combine the advantages of the lively, handy two-stroke speedster with the advantages of the high-traction four-stroke engine. Little displacement for revving and tamed engine reactions; compact motor design to implant the unit in a handy chassis. A year later, the series versions of the revolutionary bike YZF 400 followed. 50 HP and 110 kg total weight for the crosser; 45 hp and 120 kilograms for the enduro. World championship successes and the unthinkable first Supercross race victory of a four-stroke engine proved the power of the design. Two overhead camshafts and bucket tappets for actuating the five valves result in high speed stability. The YZ turns easily up to 11500 rpm. Decisively more cubic capacity – theoretically more power – than the 426 cm³ selected for the 2000 model prevents the increasing mechanical load on the unit. In addition, the inevitably heavier piston and the more stable connecting rod drastically reduce the ease of turning. With EXC Racing, KTM has chosen a conservative approach with just one camshaft and rocker arms to operate the four valves. But the design disadvantages, such as the maximum speed of around 10,000 rpm, also offer advantages: The small space requirement for the cylinder head enables the KTM engine to be installed in an almost unchanged two-stroke chassis. One of the reasons why the KTM is currently the lightest four-stroke off-road machine at just 112 kilograms for the enduro and 105 kilograms for the crosser. The American bicycle manufacturer Cannondale wants a 400 cc four-stroke cross machine with an aluminum frame and in-house engine. The highlight: the outlet is at the back, the inlet at the front. In this way, the double-cam engine can lead the intake tract vertically downwards from the air box placed under the tank, promoting performance. The outlet to the rear allows a large and – ideal for good handling – low-mounted radiator on the two frame front pipes.
Technical data KTM 400/520 EXC Racing
KTM 400/520 EXC Racing engine: water-cooled single-cylinder four-stroke engine, an overhead, chain-driven camshaft, four valves, rocker arms, a balance shaft, wet sump lubrication with two oil pumps, a Keihin flat slide carburetor, 0 39 mm, contactless Kokusan CDI ignition, E-starter, three-phase alternator 80 W, battery 12V / 4Ah.Bore x stroke 89 x 64 mm (95 x 72mm) Displacement 398 cm³ (510.4 cm³) Rated power: 32 kW (44 PS) at 8000 / min (EXC 400) 40 kW (54 PS) at 7500 rpm (EXC 520) Max. Torque: 43 Nm (4.3 kpm) at 6500 / min (EXC 400) 51 Nm (5.1 kpm) at 6250 / min (EXC 520) Power transmission: primary drive via gear wheels, hydraulically operated multi-disc oil bath clutch, six-speed gearbox. Single-loop tubular frame with split beams, upside-down telescopic fork, sliding tube diameter 43 mm, two-arm swing arm made of aluminum profiles, central spring strut, directly articulated, front disc brake 0 260 mm, rear disc brake 0 220 mm. Tires 90 / 90-21 front, 140 / 80-18 rear Chassis data: wheelbase 1481 mm, steering head angle 63.5 degrees, caster 115 mm, spring travel f / r 295/320 mm. Dimensions and weights: Seat height 925 mm, empty weight 112 kg, tank capacity 9 liters Price: still open
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