Similar to BMW with its horizontally opposed twin-cylinder boxer motors, Ducati has built a tradition, now going for more than 40 years, on its 90 degree L-Twin motors and desmodromic valve actuation. Traditions build history, develop a following, and become one and the same with the brand. Although being great marketing tools, tradition can also become a hindrance to development and innovation when the original format imposes physical challenges when the time calls for evolutionary change.
But just when you think Ducati and BMW have been cornered by an old format, ingenuity and technology have paired up to leap frog these old motors into innovative machines. That was the case for BMW when they developed the mixed liquid and air cooled boxer motor for their 1200 line which resulted in a more compact package than the original, despite the introduction of water cooling. And it has been the case on several technological evolutions to Ducati’s L-Twin motors during these last 40-something years. The introduction of variable timing to its desmodromic valves, what Ducati now calls Desmodromic Variable Timing, or DVT, is probably one of the most outstanding evolutionary upgrades to the L-twin motors. More than that, it will be a new platform for more innovation for the Ducati motors.
There is no question about the benefits of variable valve timing. Valve timing has been a challenge on the design of internal combustion motors since its invention, where a compromise has always been imposed: you want no overlap on timing for intake and exhaust valves for low speeds or street applications and for better fuel economy, rideability, and emissions, and you want maximum overlap for more horse power on higher RPMs for racing applications. As a result engineers configure motors to operate somewhat in the middle, getting an overall good performance for road bikes. But as result the motors get denied of the benefits given by operating on either end of the intake/exhaust valve overlap spectrum.
Ducati’s Superbike 1198 motors which are the basis for the 1200 Multistrada motors are a great example of how manufacturers have been operating under this challenge. The 1198 Superbike motor operates under a wide 41 degree overlap on intake/exhaust valve operation. The street variation of this same motor, the Testastretta (Testastretta means narrow head in Italian), operates at a narrow 11 degrees of overlap.
What makes Ducati DVT so exciting
Variable valve timing is nothing new in the motor industry. And it has been in motorcycle applications for several years already, most notably on Honda’s VFR line and its V-TEC motors. The V-TEC application, however, is in essence two fixed stages of operation. A solenoid in the rocker shaft will activate a different set of rocker arms at a higher and pre-determined RPM level and these different rocker arms are moved by a different set of lobes in the camshaft, with a more aggressive valve operation. That is, V-TEC operates two discrete set of intake/exhaust overlaps. Kawasaki’s VVT (on Concours 14) actuates in a continuous form, but it operates only the intake cam.
Ducati’s DVT is a true continuous variable cam which allows for countless variations on degrees of valve overlap. And it is the only one on the motorcycle industry that operates both the intake and exhaust valves. Although it seems like a small upgrade from what has already been available in the motorcycle industry, and it has been available in the auto industry for a while, it solidifies another threshold for the motorcycle industry. And it will certainly be a platform for subsequent innovations on the programming side of equation, as variable timing of intake and exhaust valves opens up an important set of parameters that can be manipulated to improve a motor’s efficiency and performance.
The intake and exhaust camshafts on the Testastretta DVT are allowed to operate at several degrees of variation from the camshaft pulleys’ position, giving a combined variation of 40-50 degrees of operation when let’s say the intake camshaft is advanced to the maximum position and the exhaust is delayed to its maximum position.
Ducati’s Desmodromic Variable Timing (DVT) Actuator
One of the ingenious elements of this design (although not unique to Ducati, as it has been used in the auto industry) is that this actuator is located inside the camshaft pulleys. The actuator is a very small part, by the way, probably 40mm in diameter since it fits inside the pulleys.
The outside portion of the actuator moves together with the pulley where it is attached by those three bolts clearly seen on the two above photos. According to Ducati, the inside portion of the actuator is moved by a hydraulic system, which is triggered by a set of electronic sensors that compares the cam shaft position with that of the driveshaft to determine the ideal timing according to specific running conditions. Seems brilliant and simple in concept.
At minimal overlap, the intake valves delay their opening and the exhaust valves advance their closure so that the simultaneous open position of both valves does not occur improving the engine’s smoothness and fluidity at lower RPMs.
The system can operate at various degrees of overlap, moving intake and exhaust cams independently and governed by the ECU. The ECU is mapped to select the position that optimizes power delivery, torque, smoothness, and fuel efficiency based on the rider’s varying throttle input and resulting engine loads. Can you imagine how much tuning you can get out of this setup? Or would it be necessary? Maybe you want to create a bias for the lower (urban mode of sorts) or higher RPMs (sport mode) of the spectrum. By the way, will it play a role on the four riding modes with low and high acceleration? Probably yes. And probably with more variation to the tune that at present levels (100hp low and high, 150 low and high).
At maximum overlap the intake valves advance their opening while the exhaust valves delay their closure given the engine its most aggressive performance.
The result of all this? Ducati claims the following figures:
When comparing this motor’s specs to the previous Multistrada models, it shows a great step in horse power and torque performance. And with that it gets closer to the Superbike’s horse power, and even beating it on the torque department, probably a reflection of operation at lower levels of valve overlap on a broad range of RPM. Obviously, defeating compromises this motor brings an overall better performance when compared to both the 11 and 41 degree motors, except on horse power when compared to the Superbike motor. There must be more to it, of course. But this simple comparison shows promising results.
All of this is useless, though, if we don’t know what it feels like when riding the motorcycle where this motor will be applied to. The numbers I like to pay attention to are the torque figures. This is what, in my opinion, makes Ducati motors especial – those high torque figures at low RPM give the perception that the motor offers effortless performance on acceleration starting from low down on the RPM engine. By all means, this new motor seems to really benefit from DVT, cranking torque figures to a nice curve and peak level.
I can’t see anything wrong on this, especially because Ducati indicates maintenance service intervals are maintained (15,000 km (9.000 miles) / 12 months), so is valve clearance check (30,000 km (18.000 miles)). Ducati also mentioned an anti-knock sensor for this motor, high compression pistons derived from the Diavel, new drive belts and belt covers, new oil pump with 70% higher efficiency, and improved crankcase for better lubrication.
And let’s not forget the improved fuel efficiency. I’ve gone more than 200 miles with a tank of clear gas on my 2013 Multistrada. But once you approach 200 miles, you better be sure there is a gas station close to where you are. This new motor will be yet more fuel efficient, making a 200 mile range a more common occurrence.
We also want to direct your attention to one number and parameter on the Ducati’s specs, the -78% IMEP COV. It is something that we have not seen discussed anywhere on forums and reviewers of this motor so far. What is IMEP COV, a “smoothness index” Ducati says? And what a 78% reduction may represent from a rider’s perspective?
Of all variables posted by Ducati, IMEP COV shows the largest gain for the DVT motor. Because Ducati thought it important enough to publish IMEP COV numbers we decided to investigate more about it. It is not something sexy like HP, or something serious like torque, or something practical like fuel economy. But it is a fundamental parameter on engine development. Touted as a “smoothness index” by Ducati, our short and superficial research led us to some important and interesting findings.
All of us have learned along the years that fuel injection motors when combined with strict emissions standards have pushed motors towards operating at the lean side of the spectrum, making certain motorcycles, especially single and twin-cylinder bikes but not exclusive to them, practically unrideable at low RPMs. That was especially the case for the first version of the 1200 Testastretta 11 degrees motor. Owners of those bikes spent thousands of dollars, and we are not exaggerating here, on full exhaust systems, re-programmed ECUs, dynamometer time, and some home other tuners gadgets to resolve this issue. And it never completely cured the problem. Despite some improvement on engine stability from all this aftermarket work, the hesitation at low RPMs and abruptness off idle was always there.
The dual spark motor of the 2013-14 models showed great improvement on this issue. When we tested the 2013 bike in comparison to a 2010 bike we noticed considerable improvements on the motor’s rideability. The dual sparks associated with a changed angle of the fuel injection and a few other changes improved torque delivery and fluidity of the motor at low RPMs while increasing torque at the same time. Although the torque increase on the 2013 model was really small, it specifically improved torque delivery at low RPMs. And that motor also improved fuel efficiency by a good 10%.
But with the DVT motor, Ducati is raising this bar to a much higher level, presenting this 78% reduction of IMEP COV which we assume is a figure derived from a comparison to the already improved dual spark motor.
Engineers the world over have been designing motors on the envelope determined by three main conflicting sets of variables: more torque and power; better fuel efficiency and lower carbon emissions; while maintaining the motor’s running stability. ECU-based fuel management systems have optimized motors to expand the limit of lean burn operation to improve fuel efficiency and reduce exhaust gas emissions without compromising power. But lean burns increase cyclical variation in the combustion intensity, which directly affects the rideability. This is what we experienced in the 2010-12 Multistradas for example and so many other motorcycles since emissions regulations have become more stringent. This rideability effect is measured by the coefficient of variation (COV) of the indicated mean effective pressure (IMEP).
Although the consumer has little access to this information, we actually experience it when riding our fuel injected motorcycles and we all know it is a lean fueling issue resulting on cycle to cycle variability. Too much cycle to cycle variability, however, challenges lower idle speeds and engine stability. Therefore, when Ducati claims a reduction of 78% on IMEP COV on the DVT motors, they are basically saying variable intake and exhaust valve timing along perhaps with other parameters, has reduced cycle to cycle variability, as measured by the indicated mean effective pressure or IMEP. IMEP is a measure of the average pressure over a cycle in the combustion chamber of the engine. The pressure stability from cycle to cycle, IMEP COV, shows high correlation to a rider’s subjective rating of an engine smoothness.
As a result, we assume these motors can run a leaner mixture, which explains at least partially the improved fuel economy, without compromising rideability. In fact, it has improved engine smoothness substantially from a more stable fuel burning cycle to cycle which helps with emissions, which we believe is the main push for this technology. A virtuous cycle of sorts.
This motor is going to be introduced as the most important and significant change to the 2015 Multistrada line up which will be announced at EICMA in a few weeks from today if not earlier than that. The 2015 Multistrada will have other changes besides the new motor. We will make sure to report here when the new bike is announced.
How will this new motor relate to the Ducati riding experience? Those high torque figures entice me and likely will improve that effortless power delivery feeling these motors produce. The 78% reduction on IMEP COV will make it much more rideable at lower RPMs. According to Giulio Malagoli, Ducati’s Head of Product Marketing:
…this motor is state-of-the-art with a mission: to be used the way you want, interpreted the way you want, and without compromises.
I will know what these words mean and I will report my experience here as soon as a demo model becomes available at the European Motorcycles of Western Oregon, assuming those nice folks at the shop will let me ride it.