What’s so good about V4 engine?

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We’re living through exciting times in the motorcycling world. With all the big factories spunking massive amounts of cheddar on R&D, engine technology (as well as electronic and chassis tech) is improving year by year by year. Ducati in particular, famed for pioneering technology such as Desmodronic valves systems, have more than done their bit. Now, not only are they slotting V4 motors in their superbikes, but their adventure bikes (the Multistrada V4 range) are benefitting from them too. But why? What’s so bloody good about the V4 engine configuration, anyway?

Aprilia have been using a V4 engine for a decade in their flagship litre sportsbike, and it’s worked pretty well. And as we all know the V4 is starting to become more prevalent in superbike showrooms. Some say it’s only a matter of time before we see a V4 Fireblade. Don’t forget, an important element of Grand Prix bike racing (and car racing for that matter) is to develop new ways to push the boundaries of performance with a view to having that tech eventually trickling its way down to production models. We’ve seen it in tyres, electronics, aerodynamics as well as engines. Now with so many top GP teams running a V4 engine there’s little doubt that we’ll be seeing more and more in the years to come. But where did it all begin?

In the beginning

Well the first V4s were designed and manufactured by a Parisian bloke called Emile Mors, but he only used them in cars, for some reason. It wasn’t until the 1930s when Matchless started to use them in models like the Silver Hawk, that they were considered suitable for bikes. Fast forward 50 years though, and although there had been a spattering of V4 motorcycles in the meantime, the 1980s was the golden era of sexy new two-stroke and four-stroke V4 bikes. I’m talking about things like the Suzuki RGV 500, Honda VF1000R and the Yamaha V-Max, to name but a few.

Since the ‘80s there’s been a real smorgasbord of V4s spilling out onto the racetracks and the roads. And plenty of them have captured the hearts and minds of motorcyclists the world over. It’s easy to see why, with their perfect balance of torque and power. Not to mention the erection-inducing sound. What’s not to like? It’s a fact that there has been some jolly impressive motorbikes utilising V4 engines.

It’s true that, as well as the orgasm-inducing noise, there are some real advantages in the performance department. For starters, there’s the lack of ‘inertial torque’. In simple-ish terms, this is the turning force applied to the crankshaft due to the mass of a ‘slowing down’ piston acting against the accelerating mass of a ‘speeding up’ piston. When these two (effectively) opposite forces are applied to the crankshaft in different places it creates a large turning force. Think of it as the pistons giving the crank a Chinese burn. Because in a V4 engine, opposite pistons are linked to the crank at the same point, they don’t try and twist anything, they just work together to turn the crank.

Chinese burn

Not only does that give the rider a much better feel for the tarmac, it gives the tyre and the entire drive train an easier time because all the ‘pulses’ from the engine are acting in the same direction. A lot of the other manufacturers have emulated this by using cross-plane cranks in inline-fours (like the Yamaha YZF-R1); a crank with 90° between crankpins alleviates this ‘inertial torque’ in exactly the same way.

Another way that the cross-plane crank engines emulate the V4 is in their firing order. A conventional inline four fires every half a rotation of the crank (every 180°). A V4, on the other hand, has an uneven firing order, typically having a 270° pause between the fourth and then the first cylinder firing (so, once every two turns of the crank). The theory is that this pause gives the tyre time to ‘relax’ back to its original position and key into the road surface, giving you more traction when really getting the hammer down.

Size matters

One quality of the V4 engine that the cross-plane crank can’t mimic is its size. Because in a V4, two conrods can be connected to the crank at the same place, the crankshaft can be shorter. So the shorter crank means a more compact engine, right? Well yes and no. It means the engine, and therefore the bike, can be narrower. That gives the bike a tighter feel and allows bonkers amounts of lean angle. But the length (the front to rear dimension) is massive compared to an inline-four which can often command a long wheel base; not always great in a sportsbike. In the case of the RSV4, Aprilia have tightened the V angle to 65° to try and alleviate this; and in doing that, have created one of the best handling sportsbikes going. But tightening up the V angle is not without its disadvantages.

An important consideration during the design stage of a V4 bike engine is the possibility (or probability) of overheating rear cylinders, due to a reduced amount of airflow. A tighter V angle means even less airflow resulting in hotter still rear cylinders. It also means you need small hands if you ever decide to do any work in or around your engine. It can be a tight affair, even before you try and squeeze two banks of inlet systems between the cylinders.

Faux pas

Despite the many and varied qualities of the V4 engine, they don’t come without a faux pas or two. With complicated (therefore expensive) designs and double the ancillaries (i.e. cylinder heads), to date V4 motors are still the reserve of the relatively high end motorcycle. Some say that Yamaha have hit the nail on the head with the best of both worlds cross-plane crank. Others would argue that’s merely a half measure.

So what’s next? Have we had the golden era of the V4 motorcycle? It’s easy to see why the major Japanese manufacturers steered away from V4s over the last two decades; they’re complicated and expensive to manufacture (there’s two cylinder heads to start off with). But will Japan reach the limit of inline four-pot technology as Italy appear to have done with the V-twin? Will we see more V4 motors making their way into genuine production sportsbikes? Or is it just a fringe movement that will never catch on? Well, when you look at how many GP bikes are powered by V4s, it’s a technology that’s hard to ignore. A technology that I think we can all look forward to seeing a lot more of in years to come.


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