High vs Low RPM motors

Oneupmanship is everything...
This guy has the right idea.
http://thekneeslider.com/radial-engine-motorcycle-2/

Any chance any of those V12's are based on Straight 6's? Internet didn't turn up much, but there are other benefits to having no bank offset.

Eliminates offsets in intake runners to a common plenum.
Makes exhausts exact mirror images, no offsets to accommodate
Cam drive for both heads 'in plane'.
Block main webs can be thicker, and no piston travel clearance machining.
Faster and easier machining of block bores (remember no CNC in 20s and 30s when many of these were designed).

Interesting, looking things up, that the first Allison V-12 V-1710 had no crank counterweights. Of course with a bore offset, you could also get away with that, but it would take seriously strong bulkheads and main webs to distribute those forces.

...and while I am at it here is a link to something I found that currently holds my fascination...

http://hildstrom.com/projects/boxer/index.html

One thing to consider as bearing width narrows (split rod or even grooved bearings in modern engines) is the hydrodynamic wedge does not have an even load distribution. Near the edges of bearings the oil can leak out the side rather than all be drawn through radially. I've seen load distribution graphs and they look like an upside down flattened parabola. So when you split a bearing into two half width sections, you'll need to add total bearing area.

A benefit to the narrow sections is higher oil flow so they will run cooler than the inner bearing (peak bearing pressure being equal), but as you can imagine if you had old F1 tire like grooves in the bearing, it will run cool until the load capacity is reached and then things get hot real fast no matter how much oil you've got.

Another problem with forked anything is load distribution is never even to the two sides due to dimensional tolerances. So you'd have to protect for some amount more than 50% of total load dependent on tolerances and system compliance.

The enormous diameter main bearing idea is certainly not new. If the mains are made a larger diameter than the crank throws, the crank is installed axially into the end of the crankcase.

The Offenhauser four cylinder race engines were built that way, with splash fed roller main bearings that never wear out. Very strong, very stiff, and low friction.
Here is a picture of a bare Offy crankcase.
http://img.photobucket.com/alb...20Print/IMG_2571.jpg

Forked conrods have been used in quite a few successful engines, and as far as I know have never proved to be a design weakness.

The main rotational conrod bearing surface is always one piece and made full width, the knife and fork part just oscillates back and forth with changes in relative conrod angularity, so lubrication is less critical. You only require one oil hole in the crank, not three.

Yeah the guy who wrote that doesn't have the background to understand the tribology behind it but the the concept seemed sound. Balancing the system wedges would be an interesting problem to work out. Also after seeing the speeds that the Honda oval piston engine were running and the period that the engine was built, a twin rod piston has had some practical success even though a different configuration. The design of the engine would be very interesting if paired cylinders were brought in plane.

When it comes to perfect balance, the ninety degree Vee twin with cylinders in line, and with forked conrods is probably the best solution.
Boxer engines come close, but the crank throws become problematic.

60 degree V12's are smoother in mechanical balance as well as torsional excitation than a V8's. The history of airplane engines as well as race engines have always favored them for that,fashion,etc. Boxer 12's even more so but most flat 12's are actually 180 degree V12's and not a true boxer engine. Here is a neat graphic on it as well as some other great engine links...

http://www.epi-eng.com/piston_...m_piston_engines.htm

...if I had my druthers I would have do 5 liter flat 8 (103mmx75mm) with the Coxial Flat Twin setup so it would fit in my 95 Impreza project car I am building. I would prefer a 12 cylinder but an 8 is the largest that will fit and it would still sound pretty awesome. Here is a 3 liter version...

http://www.youtube.com/watch?v=2lNm_bQEbCM

http://www.youtube.com/watch?v=8Z0rjor-s1w

...and just for fun a very cammy 1.5 liter (180 degree flat 8 i think i.e. not boxer)...

http://www.youtube.com/watch?v=DItHwFZUzk0