Reciprocating piston engines have changed a lot over the last 100 years or so. Fuel injection, variable valve timing on overhead cams, and distributorless spark ignition are just a handful of technologies that have revolutionized the way engines work. Despite so much change, though, one thing has remained the same in all this time—pistons have stayed round.
Ferrari is eager to change that, however. As covered by AutoGuide, the Italian manufacturer has filed a new patent for a V12 engine with pistons of a very unique shape. You might call them oval, but more accurately, they’re a “stadium” shape—featuring rounded ends with straight sides.
The simple fact is that round pistons exist for a reason—they’re easy to manufacture and they do the job well. Regardless, Ferrari has its reasons for going off-book. In this case. It all comes down to packaging.
Ferrari loves V12s, but they have one major drawback—they’re quite long. The hope is that by switching to these straight-sided oval cylinders, it would become possible to pack them closer together without reducing total cylinder volume. This could help reduce the length of the engine, enabling a large-displacement V12 to fit in a smaller engine bay.
Funnily enough, one could argue that you can’t call them “cylinders” in an engine like this, since they don’t have a round cross-section. Geometrically speaking, they’d be… stadium prisms? Argue about the terminology in the comments.
The innovation doesn’t stop there, either. In tandem with the oval cylinders, Ferrari has designed the engine so that opposing pistons can share a single connecting rod. Normally, each cylinder would be a little offset (i.e. not directly across from) to the one in the opposing bank so that each piston’s connecting rod could mate with its own spot on the crankshaft journal (sharing a crank journal isn’t uncommon).
Ferrari was able to combine the connecting rods for two pistons by adding a pivot on one side. This allows pistons to mate with the crankshaft with a single bearing. This allows further reduction of the engine’s total length.
Overall, the idea isn’t entirely novel. Honda famously built an oval-piston engine in the late 1970s. It was employed in the company’s NR500 racing bikes, which competed in the World Motorcycle Grand Prix series.
Notably, Honda followed this route for different reasons. The oval pistons were selected to allow room for eight valves per cylinder, which Honda believed necessary for its four-stroke engine to produce more power than its two-stroke rivals. Primary challenges involved figuring out how to machine functional oval piston rings [Ed Note: This was my first thought: Oval piston rings?! -DT] and to build robust dual connecting rods for the unique engine. The engine notably also aligned the pistons with the long edge parallel with the crankshaft, so it didn’t feature the packaging benefits of the Ferrari design.
There are no major mentions of the valvetrain in Ferrari’s patent. Regardless, it could follow in Honda’s footsteps and leverage the oval piston shape to fit more valves into each cylinder.
It’s unclear at this stage whether Ferrari plans to put such an engine into production. If it wished to do so, it would have to solve the issues around sealing oval pistons in their bores, and master the construction of the complicated pivoting connecting rods. Even with due attention, it seems unlikely such a complex engine design would reach the same longevity as a conventional round-piston engine. Still, given the low mileage seen by so many Ferraris, it might not be a major concern.
Image credits: Ferrari, European Patent, Honda, Ux z CC BY-SA 3.0
It’s all fun and games until someone shows up in a Speirling. I’m sure Ferrari can also build a car that exceeds the drivers ability to withstand the forces. At some point, we’re back to slot cars watching from the outside.
I’ve been taught to call that a complex linear extruded shape. Both the Honda and Ferrari implementations offer more displacement in the same block volume, similar to square bottles in a box. Then compound that with two pistons on one rod bearing?;If cost, complexity of manufacturing and cost of required precision all fall under “no object” it’s brilliant. Outside of F1/luxury performance….
I wonder if it will have a unique sound?
The connecting rod solution is the real story hear. Oval pistons are certainly VERY clever packaging, but I absolutely love that connecting rod solution, EXPERTLY clever.
Well, Lancia and Volkswagen came up with best solution for shortening the long engines…
If I recall, the NR500 engine had one of the highest specific power per litre for the production vehicle: 130 bhp from 499cc (1983), 261 bhp per litre. Currently, Mercedes-Benz comes close to that with its 350 kW M139L engine fitted to C 63 S E Performance (248 bhp per litre).
The VW “VR6” is a cheaper V6, not a shorter straight six. Great marketing though.
No, you are totally wrong. VR6 isn’t even V6 in a sense of having two separate banks of three cylinders each at between 45 and 90 degree angle along with one or two camshafts per bank. VR6 is a single bank with six cylinders placed in V-form at narrow angle, sharing the common intake and exhaust manifolds as well as camshaft(s).
This design makes VR6 shorter than straight six. Volkswagen call it VR6 since it has cylinders placed in narrow-angle V-form (10.5 to 15 degrees) inside one block (Reihenmotor, German for inline engine).
You need to quit trolling the commentators with idiotic brainfarts…
It’s a V6 engine in the sense that the cylinders are in the shape of a V. It has two banks of cylinders with an angle between them.
A straight six has six cylinders in a single line. There is a fundamental difference in terms of engine balance, but it’s the basic geometry of the layout that makes an I different to a V.
This isn’t a brain fart, this is how engines are classified. I design engines. Having separate heads makes no difference, it’s having any bank angle at all that makes it a V.
Sure it’s shorter than a straight six, a V always will be, it’s why they’re so popular, and also don’t suffer from whippy cranks like an I6.
The clever bit about the VR6 is that it’s much, much narrower than a traditional V, and cheaper, and only has one hot side so it’s easier to fit transversely. The marketing really pushed the comparison to inline engines because that’s what BMW were selling.
VW’s W-12 (etc) engines were also designed to be (relatively) short.
Motherfuckers.
Last year I drew up a proposal for an inline six of the same capacity and length as an inline four. All the smoothness of a straight six, less inertia than a four and no packaging penalty. The trick was the comedy piston shape. Just like this sodding Ferrari V12. I started with a Honda NR and realised they’d “ovalised” it the wrong way (albeit for the right reason in racing). I guess this kills any chances of my project ever going forward.
These aren’t flat sided pistons with a circle at each end. What looks like a flat side has to be a slight convex radius or the rings won’t seal. The Honda was the same. Christ knows what the geometric name is for two opposed pairs of radii with with tangential joints and two planes of symmetry at 90 degrees. Is it a special case of a salinon? We need a bigger geometry dork than I am.
With my engine (2.0 straight six) the long axis of the piston was 86mm, a pretty standard bore for a 2.0 four, so piston rocking isn’t an issue. No issue with the speed of the flame front either.
I went for 5 valves and while the inlet flow area wasn’t an improvement the perimeter flow area was, so you get more flow at lower lift. So overall better gas flow than either a traditional round 4 or 6 cylinder engine of the same capacity.
Dammit. This was the most exciting thing I had in the pipeline, and now Ferrari’s lawyers will be all over it.
How were you planning to deal with the piston rings?
The same way Honda did.
The legend goes that Honda’s engineers were at an impasse trying to fit more valves on a cylinder, then one day one of them was stuck in traffic and looked at the (horizontal) pack of traffic lights, whose housing has the obround shape. It looked like three cylinders in an oval (obround actually) block, and he thought what if this whole area was useful piston area.
I know I’m old enough when I realize that I was an adult when the NR750 was released…
It cost north of $50k back then, and it sold out quite fast. Rumor was that most of the units sold were bought by engine manufacturers. Maybe some patents have expired ?
Besides the complexity and price, it was all pure benefits. The Honda engine was effectively a V8 with siamese-d pistons, mostly in a V4-sized form factor, EXCEPT that it had:
1) More useful cylinder volume for the same physical size of the cylinder (the two extra “triangular” wedges that occupy the space between two round pistons put one next to each other, if you look from the top – an oval has more area than two circles put together)
2) Less friction than if it was two round pistons – once again, if we look at the imaginary almost triangles – with the “oval” piston there’s only one side of the triangle that contacts the cylinder wall – an oval stadium would have a shorter fence than two round stadiums put together.
This… seems entirely too complicated.
If the Japanese did the oval pistoned V12, I’d have some faith in it, but not the italians…
Interesting. Do I trust Italian engineering to make it work reliably? Fuck no.
If you have money for a Ferrari, you don’t care about reliability !
Honda used oval pistons in the NR500 to get around the FIM ban on V8 engines. It was also an opportunity to show off, and Honda’s first product was piston rings. Ferrari isn’t trying to work around a racing rule, so this is a lot of work to save 8 to 12″ but could pay off if there is also a super short V6
I believe the term of art for this shape is actually SQUIRCLE.