Many good points made here.

With regards to roller bearings in 4-stroke engines:

Interestingly enough, many aircraft and Grand Prix racing engines before and just after WWII utilized main and rod rollers bearings. Some had split roller bearing and some used dismountable Hirth crankshafts.
The direct injected and inverted V 12 DB 601 of the Messerschmitt 109 and 110 (appx 1940) were roller bearing engines. Later going to hydrodynamic bearings after the fall of their bearing manufacturer in 1942. Engine development had produced a more powerful engine regardless.

Early Fiat 2 liter engines (appx. 1922), Bugatti 35 B & 35 C (~1930), AlfaRomeo P2 (1932), Tipo 159 (~1951)
Merecedes W 25 (1934), M154, M163 (1938-39), W125 (1939), M 196, were all examples of engines using roller bearings. Many of which were upon consequent rebuilds changed over to fluid-film.

The Porsche 356 unit which was another example, with a Hirth manufactured crankshaft. It was used in early Porsche racing and some street engines (1500cc, Carrera, etc.) into the mid 50's. Very reliable engines too.

Honda has released alot of data in regards to engine performance testing utilizing roller bearings and the results are rather interesting. Seems the largest gains are not necessarily in reduced friction (as a hydro bearing is extremely efficient) but in the reduction of power required to move the oil. Many engines are still using roller bearings, mostly of the hybrid angular contact type... and ceramics look promising.

On V-angles:
There have been engines built on just about every v-configuration imaginable. 15º Volkswagen VR and W-series, 60º, 72º, 75.5º (Honda RC211V 5-cylinder four-stroke), 80º, 90º and wider. Problem with the wider-than-90º engines is in the harmonics, countershafts help the situation but it generally gets worse the wider the angle. The engine also loses a good deal of ridgity in those configurations. Lower center of gravity... yes, just as Bret mentioned. But it comes at a price. With some work it can be made to work as Renault has shown, but is it the right direction???

To reduce frictional losses (fmep)... you can use low tension rings as mentioned, you can use shorter piston skirts, coated piston skirts or pistons of special metal matrix composites. Gets expensive in a hurry. You can also coat cylinder bores with nikasil as Porsche and many high end racing engines have done for a few years now to lower the friction coefficients. As the saying goes, "Every little bit helps". Reductions in crankshaft windage, improvements in counterweight aerodynamics, all add up to very small gains. Not feasible for production level engines but in motorsports where money is no object, these are very feasible areas of development.

The rest is pretty much limited in the design. Ever wonder why anyone would build a small displacement V12 or V10 engine? Take your 350 cid and divide it up among 10 cylinders and you have a much shorter stroke, you have smaller cylinders and better combustion, better piston cooling, inertia forces which are easier to balance, reduction in thermal stresses.... the list goes on.

Maybe some more on this later.

Take care

 

Always wanted to learn more about that. The other things, like piston coating is easier to do, but I never got into in the nikasil. For me that's up there with the laser etched cylinder walls.

BTW you mentioned the additonal cylinders for better combustion. What do you think is where the law of diminshing returns comes in on bore size w/ a single plug? I've read things mentioning 4.500" could be before that or after that. Seems to me that the width of the chamber makes more sense, but 10-20 deg before/after TDC you far enough into the cylinder where the bore would matter more I guess.

Bret

 

An interesting note in regards to the post above by SStrokerAce. They are running dual plugs on these very small chambers, which I thought was odd. I think they were 1.3 liter motors.
Are there any disadvantages to offsetting your piston pin, such as odd loads on the piston at other points besides the power stroke? What about shortening the piston skirts? Would the piston have a tendency to rock in the bore?

Thanks!


Don

 

Not sure about the pin locations short commings.

The dual plug idea is really good, causes a more efficent burn of the fuel by having two flame fronts. F1 guys must be doing this to burn the fuel faster to allow that kind of rpm with that big of bore (around 3.7", if they have as small of strokes that I think they do)

Yes, if you cut down the skirt to much it will cause a rocking of the piston in the bore. The rings and the skirt are basically what prevents that. Having a N2O or Boost ring pack and a short skirt cause the piston to rock in the bore alot more than a low power NA ring pack and a long piston skirt.

Bret