21 replies to this topic

[Nira]

Having completed the 500th win in the first GP of this season when Valentino Rossi crossed the line in Suzuka, the decision was taken that this should be the occasion to bring out the highly publicised machine, the day before Yamaha intend to have their new four-stroke bike circle the Montmeló track. The engine distinguishes itself from the current two stroke machines for a number of technical reasons. The name of the new machine is RCV211. RC represents the traditional Honda racing brand, with the V representing its V5 configuration, whilst the number 211 stands for their first motorcycle of the new 21st Century racing generation. The V5 engine uses circular pistons (3 in front and 2 behind), despite speculations over them being oval. There are 4 valves per piston featuring a PGM fuel injection system. The weight of the engine is that of the NSR 500 x 110%, and it has a capacity 990cc.

Can anyone explain the advantages and disadvantages of oval pistons? There was talk that both Honda and a German manufacturer planed to release cars with oval pistons a few years back, but I have not heard anything lately.

[Top Fuel F1]

Other than Oval Pistons not being legal in F1, there must be some reason to even have some people thinking about them. One thing for sure, it would make the block's dimension greater in one direction and shorter in the other, depending in which way it was orientated. For that matter it could in any orientation. That is not just with the oval's longest dimension facing either to the front of the block nor to the side of the block. Also I don't know if the is any significant tendancy for any given round piston to try to rotate in a round cylinder .ie exerting some twisting force on the rod. If there is maybe that would be a reason.

[MN]

V8 engines are not allowed therefor oval V4.
8-valve/cyl, 2 con rod/cyl, short stroke, high rpm, V8 effect with V4 configuration... maybe ;)

[GSXRTURBO1]

Oval pistons allow a LOT of valve area, so they have the potential for flowing massive amounts of air. The drawbacks are expense, for one, and complexity/difficulty of making the oval rings to go with the pistons. Honda had an oval pistoned motorcycle awhile back - I believe it was the NC30? It had 8 valves per cylinder!

[BRG]

It was Honda's oval pistoned bike engine that made the FIA (farsightedly for once) ban it for F1 purposes before anyone in F1 had even realised that it was possible...

[marion5drsn]

The manufacture of the oval pistons and cylinders must by its very nature present a lot of problems. The measuring of the internal surfaces at the machine offer a lot of complexity. A cylinder is very easy to machine even at the tolerances of todays engines. This may be a case of making something just to prove you can do it, but does it have any practical value other than that?
It may be similiar to making a ball on a jig boring machine with a rotary table. Its possible but very expensive! Yours, M.L. Anderson

[MN]

Expensive indeed!

They were selling 750cc V4 oval street legal bike in Japan.
It was called NR750 or ZR750 or NZR750 or something like that and price tag was about 50K US$.

[GSXRTURBO1]

NR750, that must be it! I don't know why I thought it was the NC30, that must be something else Honda made.

[leegle]

Maybe there are benefits in the combusion chamber that help the combustion process, or greater control of the gasflow to benefit combustion.

[desmo]

There is some inexplicable fascination out there with the Honda NR engines. Like the Tyrell six-wheeler, they keep popping up on F1 fora. I maintain that the engine and it's derivatives were nothing more than a half-clever workaround of the FIM's 4-cylinder max for the 500GP class. Fun and exotic, yes absolutely. But there is nothing inherently superior about non-cylindrical cylinders.

[Yelnats]

So true Desmo. If Honda had their druthers they would have built a V6 or V8 to achieve the short stroke and valve area they needed. But because the rules limited them to 4 cylinders they siamesed the cylinders together and in effect produced a 4 cylinder V8.

[leegle]

I have to agree that it would have been a tricky thing because the piston rings for instance would have been very difficult to make for it.

[Dolph]

Don't oval shapes have more surface than round ones and therefore cause more ware?

[Halfwitt]

As far as the regualtions were concetrned, when Honda ran the bike like-for-like, i.e. a 750cc oval-piston versus 750cc cylindrical piston, the oval piston bike was FAR quicker. I think it was the 1987 Bol D'Or endurance race, but I'm not sure.

As for wear, if the loads are similar, for more surface area, the pressure is decreased. Therefore, I would expect wear would be less. Also, the likelihood of gross and total mechanical seizure would be less.

Incidentally, either Triumph or one of the other British motorcycle firms tried this in the 1920's or 1930's and gave up becuase of difficulty with piston rings.

[marion5drsn]

. Pistons have been made for years with cam shaped “Out side diameters”. I don’t believe that making the “Rings’ would be a problem either as that is also the same as camshaft lobes. The big problem I believe is the precise machining of the Cylinder. An ordinary cylinder is machined to a very close tolerance, then honed with fine hones and then roughed (Cross hatched) up with coarse stones to help seat the rings. One can see this at the bottom of an old cylinder below the compression ring travel. Just how one would do this in an oval “Bore” in the manufacture of millions of autos is an enigma! To the best of my knowledge even simple machines with computer controls have not been “Lazerized” to produce “Zero” tolerance lead screws. But then again someone is probably working on it. Yours, M.L. Anderson

[RJL]

It was the NR750, I believe; and it was done to circumvent the maximum four cylinder rule. There was no honda NC30 that I am aware of, but there was an RC30 (750cc V4). ZR 750 was a Kawasaki.

[MN]

Yes, NR (New Racer).

1979 500cc racing version
100 degree V4 oval
32 valve
499.5cc
115ps/19000rpm


1992 Street legal version
90 degree V4 oval
32 valve
747.7cc
125ps/14000rpm


Piston ring sealing was the biggest problem.

[Darren]

NC30 (VFR400R) is the baby brother of RC30, at least in a marketing sense. Pretty nifty little 400cc V4 16 valve machine with a single-side setup from the factory. Conventional pistons from memory. Heaps of them around everywhere, I'd imagine.

[Halfwitt]

Originally posted by MN
Yes, NR (New Racer).

1979 500cc racing version
100 degree V4 oval
32 valve
499.5cc
115ps/19000rpm


1992 Street legal version
90 degree V4 oval
32 valve
747.7cc
125ps/14000rpm


Piston ring sealing was the biggest problem.

Everybody thought NR was Never Ready

1987 Endurance Racer version
90 degree V4 oval
32 valve
747.7cc
155 - 160 hp /14000rpm (allegedly, although probably right)

There were rumours years ago of a 250 Turbo v-twin oval piston bike with ridiculous power, but this never got any further than the rumour department.

[RJL]

Oi, I remeember the NC30 now! I don't think we got them in Canada. I remember really wanting an RC30, though. There was a used one available recently at my fave bike shop and I felt the pangs all over again. Maybe NC stood for "Not Canada"?

[MN]

[GSXRTURBO1]

Ah yes, almost forgot about the 2 rods per piston...