What makes the Wankel engine so powerful? Answer it doesn't have to turn reciprocating mass in to rotating mass. Everything is rotating on the centerline. Energy is transmitted smoothly to its output. Vibration is energy loss. Many engine builders including myself, drill their cranks and counter weight them with heavy metal. There is a strobe machine that we put these cranks in and turn them up to RPM and see where the weight needs to be added to counter balance the the energy displaced by the piston moving in the other direction. This is measured in Grams and if a gram or two can make a difference on a big engine just think of how much difference it will make on a small engine. I do not have the math background to figure out how much a gram off ,would weigh at 10,000 rpm but my guess is,it would be a lot!!

Countless HRS of R&D goes into making these engines run as smooth as possible. I frequently build engine that produce 1.28 HP per C.I.D. And the torque curve is way up there. This is not a guess.

Do I build Model airplane engines? NO! I leave that to the experts, Randy Smith. Just as I do not work on my own car or operate on my self.

I think this is a very moot point. I have thought about it for years. How DO you measure the capacity of an engine? In reciprocating engines we use the total volume swept by by the piston(s) in one turn of the crank. For starters the crank in a wankel does not turn at the same speed as the rotor, which is the equivalent of the pistons. Do we measure one turn of the rotor or one turn of the output shaft? In a wankel the shaft is effectively geared from the rotor. This is equivalent in a car to the drive shaft behind the gearbox. The gearing bears no relation to the capacity of the engine. I think the capacity of a wankel should be the total swept volume of 360 deg. rotation of the rotor. I don't know how wankel volume is conventionally measured, but if only one chamber is considered, that would account for the fuel consumption and power, - your swept volume is actually 3 times what is quoted!

Vibration does rob power, but no single cylinder engine can be perfectly balanced.
Many years ago, I bought a Fox .78 from a modeling friend, he had sent the engine off to some engine guru to supposedly have it balanced and blue printed. That engine did run smooth and my friend Bill had flown it a couple a years and moved on to bigger airplanes and gas burners.....I wanted the engine for a big (9ft span) airplane, Bill, my friend, had flown the engine on pattern type planes. Any way, that particular .78 was installed and made ready to fly and to the field I went. Getting there, I proceeded to start the engine in order to tune it using a 14 x 6 prop that I had always ran on other .78s.....that engine ideled better than any engine that I had ever owned and upon advancing the throtle it was smooth as could be, but acceleration from idle to WOT seemed to be sluggish but I attempted a flight, got airborn and trimed and played a bit and discovered that when I pulled the nose up, that old Fox .78 power just wasnt there......so after thinking an tinkering, I pulled that engine out of the plane and pulled another .78 from another plane and headed back to the field, fired up the old .78 that now resided in the plane , tuned, noticed the old familer crispness in acceleration, old familer level of vibes, and got airborne, old .78 flew that airplane with authority and never slowed down when the nose was pulled up......WHAT THE HECK......the old stock .78 made power much better than the (engine guru)  breathed on one did....called my friend that I had gotten the engine from and questioned him about just what had been done......(balance) was the big thing.....decided to tear the engine down and see if I could determin why it didn,t make power like my other .78s.....Bill flew pattern sized planes with it, 7 - 8 lb range, 11x7, 12 x 7 prop size, I needed to turn 14 x 6 and fly 12 to 14 lb range...
But any way, befor tearing it down, I bench ran that engine trying to determin what ailed it, smooth as silk, ideled fantastic, struggled to turn a 14 x 6 up to where I knew that it should........
Pulled the back plate and immediatly witnessed the problem.....pulled the engine completly apart took the (balanced) crank out and immediatly got on the horn and ordered a new crank......A massive amount of weight had been brazed onto the crank counter weight and machined and dressed to perfection.......looked good, engine was smooth, ideled perfectly, but just didnt make the power that I knew that it should..
And that is what I mean by the term   (over balencing) add enough mass and you can dampen lots of vibration........Phil

Phil C, i have often said that the single best mod that could be done to a Fox Stunt .35 would be to manufacture a light aluminum ringed piston and sleeve for it...

Hey Robert; As far as engine vibes, I have an 84 Sportster. Need I say more. 

Hey Jim, I have had 3 Sporties, 57, 64, and a 74 as well as a 45, a 53 Pan and a 67 shovel.........as well as countless Triumpths, BSAs and other assorted and sundry britt bikes......Never could tell just who was winning the vibration race...:-)
Cheers, Phil

Well lets see You had a K model and two iron heads, a flat head and two more engines that they hadn't re-tooled sense 1937 and counless bikes form the prince of darkness.. What are you saying? That the late model twin cams are vibrators- Or the B engine with the 2 five pound counterbalancers in it vibrate too much?     HMMMM??? 

The K-series modernized Harley's sport bike category. The K-Model had unit construction, hand clutch and foot shift, but still ran a side-valve engine. The racing version was termed the KR, and had hot cams, valves with more efficient flow, ball rather than roller main bearings, and a magneto whereas the standard K carried a distributor. Bore and stroke were 2.75 by 3.8125 inches on the K, exactly the same as on the W-series, introduced in 1941, that the K-series replaced. It weighed 400 Ibs. and ran approximately 30 bhp. It came with a beautiful 4.5 gallon gas tank, and customers had a choice of a solo or dual seat.

Appearing in 1954, the KH had the K's bore, but the stroke was lengthened to 4.5625 inches. Displacement increased from 750cc (45 cu. in.). The transmission was improved as was the clutch. The sportier version of the KH was introduced in 1956, replete with hot cams, polished ports and was called the KHK. By this time, however, Harley-Davidson engineers knawed at the new Sportster on factory drawing boards. The KHK was not built as performance oriented as it might otherwise have been.

The XL-series hit the dealers in 1957. Labeled the Sportster, launching one of the most famous and well-termed motorcycles in history. The XL was a pure, American hot rod motorcycle. It was the first American muscle bike, and today remains the most popular machine in its class.

In 1957, the XL engine was a K converted to overhead valves. It had a larger bore of 3 inches (compared with 2.75 inches for the K), and returned to the original K stroke. The larger bore meant bigger valves and the shortened stroke meant higher rpm. Both created much more capacity for power

By the way the Vrod designed by Porsche IMO is just a water cooled flash in the pan. 63 ft lbs of torque is not going to sell this as a super bike or a touring machine. The reason the did so well in pro stock class is they were allowed an extra 60 inches of displacement over the imports. Otherwise they would still be at the starting line.

I have only been a PHD factory trained Master of technology sense 1974.