How the Honda RC213V 90° V4 Engine Makes Us Rethink the Problems with the Ducati Desmosedici

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Just over 18 months ago, I wrote a long analysis of what I believed at the time was the main problem with Ducati’s Desmosedici MotoGP machine. In that analysis, I attributed most of the problems with the Desmosedici to the chosen angle of the V, the angle between the front and rear cylinder banks.

By sticking with the 90° V, I argued, Ducati were creating problems with packaging and mass centralization, which made it almost impossible to get the balance of the Desmosedici right. The engine was taking up too much space, and limiting their ability to adjust the weight balance by moving the engine around.

Though there was a certain logic to my analysis, it appears that the engine angle was not the problem. Yesterday, in their biweekly print edition, the Spanish magazine Solo Moto published an article by Neil Spalding, who had finally obtained photographic evidence that the Honda RC213V uses a 90° V, the same engine angle employed by the Ducati Desmosedici. Given the clear success of the Honda RC213V, there can no longer be any doubt that using a 90° V is no impediment to building a competitive MotoGP machine.

The photographic proof comes as confirmation of rumors which had been doing the rounds in the MotoGP paddock throughout the second half of the 2012 season. Several people suggested that the Honda may use a 90° angle, including Ducati team manager Vitto Guareschi, speaking to GPOne.com back in November.

I had personally been lucky enough to catch a glimpse of a naked RC213V engine at one rain-soaked race track in September, but while the glimpse through the window may have been good enough to form the impression of an engine that looked like it may have been a 90°V, it was a very long way from being anything resembling conclusive, and nowhere near enough to base a news story on.

Spalding’s persistence has paid off, however. The British photographer and journalist is a common sight wandering among the garages, either first thing in the morning, as the bikes are being warmed up, or late at night, while the mechanics prepare the machines for the following day.

At some point, the Honda mechanics and engineers – protective to the point of prudishness of displaying any part of their machine to the outside world – would let their guard slip. When they did, Spalding pounced.

So why did Honda elect to use an engine layout which is blamed for causing Ducati so much trouble? And how does Honda make the layout work where Ducati have continued to fail? The first question is relatively simple to answer; the second is a good deal more tricky.

There are many reasons to use a 90°V for both four cylinder and two cylinder engines. First and foremost is that such an engine layout offers perfect primary and secondary balance – put crudely, the vibration caused by the mass of the piston moving, and the vibration caused by the difference in motion between the crankshaft and the piston (see animation here) – which means that no extra measures are required to balance the engine out.

Adding a balance shaft – as is needed for a 75°V, as the previous RC212V was, and as is needed for Yamaha’s big bang inline four – saps power, requiring around 1-2% of the engine output to drive the balance shaft at sufficient speed.

In addition to that, a 90°V also has perfect inertia torque: the torque created by the movement of the pistons all balance each other out — the same reason Yamaha chose to use the big bang firing order for the M1 inline-four. There are more reasons as well – more even cylinder firing means more manageable intake pulses in the inlet tract, from air intakes to airbox, among other reasons.

Rule changes also made a 90° V more attractive. When Spalding spoke to HRC boss Shuhei Nakamoto about the engine, Nakamoto explained that the maximum bore size of 81mm – primarily introduced to act as a rev limit – had allowed Honda to think of expanding the engine angle when they switched from 800cc to 1000cc.

The fixed bore meant that the engines required a longer stroke, moving the exhaust ports further away from the crankshaft, and making the cylinder heads higher. This gave more room for locating the rear shock; with the 800cc, the exhausts had to be kept away from the shock to prevent the shock oil from absorbing too much heat and losing damping; on the long-stroke 1000, this is less of a problem, as the exhausts are routed further away from the shock anyway.

The taller cylinders also moved the center of mass significantly; with a narrow V, that weight would have been further up; having a wider V, 90°, the weight is distributed a little better, Nakamoto explained to Spalding.

So why does the Honda work, while the Ducati doesn’t? For a number of reasons, few of which have anything to do with the engine angle. Contributing a small amount is the fact that the Honda engine appears to be rotated slightly further rearward than the Ducati Desmosedici.

Ducati had abandoned its more L-based approach, with the front cylinder bank close to the horizontal, at the end of 2011, choosing to rotate the engine back to close to 45° from the horizontal. But far more important is the location of the engine in the frame, and the arrangement of the gearbox and output shaft.

On both the Yamaha and the Honda, the gearbox is more compact, and everything is packaged more tightly. The Ducati engine and gearbox takes up more physical space, leaving less room for maneuver in terms of frame and swingarm design.

Ducati’s biggest problem, though, remains the concept around which it was built. Ducati appear to have built the most powerful engine they could ensure would be reliable, and put it in a frame. What Ducati Corse did not take sufficiently into account is the fact that a motorcycle is just that: a motor- cycle.

There are two parts to the equation – both engine (motor) and chassis and running gear (cycle) – and getting them to work together is what turns a racing motorcycle into a winner. The synergy between power delivery and handling has always been the Ducati’s weak point, even during the 990cc period.

Then, however, custom-built tires and excessive horsepower allowed riders such as Loris Capirossi to exploit the strengths of the machine – horsepower and drive – to ride around its weakness, an unwillingness to turn. With the advent of the 800’s, the Ducatis lost much of their advantage, and once the spec-tire was introduced, only the combination of the riding genius of Casey Stoner and the set up genius of Cristian Gabarrini could make the bike work, and even then, it remained horribly finicky.

The spec-tire meant that the Ducati could no longer solve the lack of feel from the front end with a specially constructed front tire. The carbon fiber subframe had been a massive improvement in consistency over the steel trellis frame for the Desmosedici, but with the spec Bridgestones built around a standard chassis layout of an aluminium beam frame, Ducati’s frameless design, using the engine as a stressed member, was doomed to obscurity.

That design was scrapped at the end of 2011, and an all-new aluminium beam frame, similar in design to those of Yamaha and Honda, was introduced in 2012. But there is more to chassis design than just copying the layout: Ducati’s previous design, using the engine as a stressed member, had placed a very stiff and inflexible lump of engine in the middle of two more flexible chunks of subframe, connecting the steering head to the front cylinder and the rear swingarm to the gearbox.

Once the beam frame was introduced, the design appeared to follow the same pattern, maintaining a central, extremely stiff section, with two softer sections at front and rear. The chassis changes through the year have had less and less material around the swingarm pivot point, for example, as Ducati searched for more flex in their chassis. The problem, however, may have been in the beams connecting front and rear, rather than in the attachment points for the swingarm and steering head.

The engine, also, retained the solid construction which had previously been required by its use as a stressed member. It was a much heavier lump than the Honda and Yamaha units, as the history of the minimum weight increase for 2012 reveals.

At the end of 2011, Dorna proposed a weight increase from 153kg to 160kg. This proposal could only be rejected by unanimous agreement of the MSMA, the manufacturers. After the MSMA met, they reported to the Grand Prix Commission that the proposal had been rejected by a unanimous vote.

It transpired that the vote was far from unanimous: one manufacturer – though it was never confirmed, it is widely accepted that this was Ducati – had voted in favor of the weight increase, and after they informed the GPC that they had been misinformed, a compromise was reached where the weight was increased to 157kg in 2012, and 160kg for 2013. Ducati had the most to gain by a weight increase, as their bike was already the heaviest of the bunch.

The heavier engine makes weight distribution even more critical. Getting the basic weight distribution right is key, and this is where Ducati have suffered most. How critical this is was demonstrated by Honda in 2012, as they struggled with the added weight and with the altered tire construction.

Both were causing huge chatter for the Hondas, a problem which it took the factory over half a season to get to grips with. Once they did get it under control – or at least, get it under control sufficiently to allow the Honda men to win 8 of the last 9 races – the Hondas were nigh-on unbeatable.

Weight distribution, chassis stiffness and flex, power delivery. These are the variables which a racing motorcycle designer is required to control to build a competitive machine. Ducati’s problems stem from the fact that they have not mastered these three sufficiently to produce a rideable machine.

That Honda should be able to do so, using the engine layout previously blamed for Ducati’s woes, speaks volumes about HRC’s resources, their engineering skill, and their experience. It is a foolish man who bets against Honda when they decide to go racing.

So I was wrong, 18 months ago, to lay the blame at the door of the engine angle selected by Ducati. I should have known better, given Honda’s long history of racing success with V4’s, in World Superbikes and Endurance racing with the RC30 and RC45.

Their 90° V engine will be the basis of their production racer (which writer Mark Gardiner has proposed be named the Honda PVT), as well as the design template for the World Superbike homologation special due to be launched in time for the 2014 WSBK season.

The layout itself is not important: it is not a matter of getting the right engine angle, it is a question of getting the engine angle right for the bike you are building. These remain motor-cycles. The two parts truly create a greater whole.

Photo: Ducati

This article was originally published on MotoMatters, and is republished here on Asphalt & Rubber with permission by the author.