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Today we present the fascinating and multifaceted world of the two wheels. Who chooses to have a motorcycle, wishes to get the best from it because being a motorcyclist is a state of mind, a way of being. The road is not only a strip of asphalt, but a breeding ground for emotions, for life. Many of our technicians are also motorcyclists and for this reason, we also want to give space to this study on a model of Ducati: Scrambler 803cc 74 HP.

Today’s study is a focus on Ducati Scrambler equipped with 74HP 803 cc Twin Engine plus ECU Siemens VDO M3C.

Scrambler by Ducati is a historical model of the Ducati brand; production of the first series started in 1962 and terminated in 1976 with 125, 250, 350 and 450cc cylinder capacities. After about 40 years, Ducati has decided to revive the Scrambler project and create a totally new motorcycle which could also adhere to the scrambler concept of its “ancestor”. (Ducati Scrambler 1962).

Scrambler is not only the name of a motorcycle model, it represents a philosophy and is derived from the English verb “to scramble” which means mixing. Scrambler was the name of road motorcycles provided with handlebars, tires and off-road ratios, in order to easily drive on long dirt roads connecting American “ranches” to public ways.

In fact, the Scrambler model by Ducati was mainly designed for the American market. The reasons for the commercial success of Scrambler were manifold. First, it had an exceptional frame (it was even used for track racing, which is probably unprecedented in motorbike history), and an engine perfectly suited for its function. It was not the fastest bike of its days, but its general performance and absolutely centered riding position, made it one of the most delightful motorcycles of the era. It was also extremely stylish: rounded lines, simultaneously classical and modern, and bright colors contrasting the black running gear and chrome tank.

The Scrambler was universally considered a balance between the American and the European schools of motorcycling. It was an extremely fashionable bike, and remains popular today.

The new Scrambler is powered by a L-Twin, Desmodromic, air cooled engine with 2 valves per cylinder, that cranks out a maximum output of 74HP at 8250rpm and 68Nm at 5750rpm.

In Desmodromic distribution the spring compressing the valve by closing the cylinder opening is removed, and replaced by a complex mechanisms provided with two small arms (leverages) which are connected to the camshaft which, in addition to the usual lobe cam, features a complementary cam, controlling the valve opening and closing.

The current system also uses a spring that actuates on the rocker arm closing the valve, so as to allow the poppet valve to perfectly close.


The benefits of this system are varied:

  • higher engine speed compared to engines equipped with springs or with the more complex and expensive “pneumatic valve” system, this is because the spring return is precise and avoids the impact between the piston and the valve, whereas the other systems imply to respect the valve return speed because flickering occurs at high engine RPM (irregular closing of valves, over-rev).
  • Low consumption: this advantage is modest and is given by the fact that less energy is needed to actuate this system, which energy would be otherwise absorbed by the continuous compression of springs.
  • Higher performance and less friction: compared to an equivalent engine with traditional spring return, an engine can run at a higher speed and, if properly exploited, this allows reaching a higher power rating.
  • Absorption given by frictions among elements is also proportional to the number of engine revolutions. This allows fewer losses at low and medium speed, compared to traditional actuation.
  • Quicker valve closing and elevation: compared to traditional systems, the valve can have a higher acceleration, obtaining a quicker opening and closing. This increased speed enables to enlarge fluid carrying times, which are always critical at high speeds. So, the use of the “desmo” system in motorbike engines reaching higher speeds than car engines, is not accidental.

Let’s now analyze its drawbacks:

  • High design and construction costs: compared to a normal spring return system, the costs for valves and camshafts designing and construction are higher
  • Imperfect closing: compared to the standard spring return system, the valve closing is imperfect because of thermal expansion and production clearance. To solve/limit the problem, the system uses a spring that moves up the lower rocket arm and improves the valve closing, but reducing the advantages of the demodromic system.

How to read and where to find the control unit?

Technical data of the control unit

  • Manufacturer: Siemens
  • Model: VDO M3C
  • Microcontroller: MC9S12XS256
  • EEprom: internal to microprocessor

The driver consists of 16 maps that are divided into the following categories: reference axes, Limiters, Injection System, Advance, Air Control, Deactivation

Focus on mapping // Basic Map Injection

It allows the engine to stop the closed loop function (when the injection is regulated to keep lambda =1), thus injecting more gasoline by high engine revolutions and load. The map depends on the engine RPM and the air percentage.

Desired Motor Load

This map represents the ideal percentage of air entering the engine, depending on the engine rev number and mBar pressure measured by the MAP inside the collector.