Wind beneath my wings

           Everyone has an inspiration, a goal, something they want really badly, or want to be with every iota of their being. When I get coffee, I see dudes that are definitely attempting to become Johnny Depp, or Demetri Martin or that really, really want to fall into an Ocean Pacific T-shirt design from when I was 12. When I was 12, I wanted to be Chuck Yeager. I wanted to shoot down Messerschmidts with my Mustang and test-fly rocket planes. Now that I've done all those things, I think I want to be Jan Thiel. Why? Because Mr. Thiel designed probably the blindingest most amazing race engine to date. Now, its possible that he has some competition by way of Yamaha's direct injection boat engines, but I can't find anything with wheels that holds a candle to the RSA. Even the Boffins at HRC & KTM are struggling to match this beast. 

           Some years back the arms race in MotoGP 125 was a dead heat, with bikes from a handful of marques pretty evenly matched. Piaggio / Aprilia was getting feedback from the riders that they wanted an engine with more torque in the upper midrange. Tuning possibilities exhausted with the current RSW engine, they sought to develop a different style of engine, and recruited legendary 70's 80's GP engine tuner/designer Jan Thiel, who happened to be alive and interested in the project. With his genius and Piaggio's resources, the results were unconventional and powerful. The RSA is a 125cc Transverse Rotary valve engine that makes a blistering 56.5hp, with more torque and 3.5 hp more than its reed valve predecessor. Without a new material (carbon this, silicon that) having been invented, a 3.5hp gain is pretty significant in a race class where the blood has been squeezed from the stone for decades. 

              Like many, when I first got into bikes I presumed that the stock rotary systems on my Vespas were garbage and that aftermarket reed valves were the only way forward. The truth as I'm learning is that reeds are the easiest way to access 97% of available horsepower, but that at the tip top, rotary is still the Hp King. Why? Because when a rotary valve opens there is no obstruction (like a reed cage) between the crankcase and the carb, optimizing intake charge velocity. And that miniscule difference in intake velocity is what gives rotary the narrow edge. A transverse rotary is even better as it dumps the incoming charge between the crank webs, just behind the cylinder transfers.  Combine all that with the knowledge that a rotary valve can be independent of piston position, and therefore successfully manage backflow and low-end issues, and you have a very spicy meatball.  Alas, the ship has sailed on all of my current bikes, they will all be reed valves. But now I'm thinking that for future efforts, I'll try to build a rotary bike. 

         I can find very little info on this motor, lots of pictures on complete bikes racing, but very little on the engine itself, or its 250cc brother. I made a graph to illustrate what an efficient powerplant the RSA is. Basically, the total power of the motor, divided by the capacity. As an example, the Yamaha R1 is rated at 172hp. If it were as efficient as the RSA, it would have 280 MORE hp. I realize the logic is kinda flimsy and my numbers are not all official, this graph is more a visual aide than anything. Not pictured: as it didn't fit on the graph is the pokey Harley Sportster 883 with a rating of 19.2. 

   

          In other news, I made another batch of Tomos/Polini/Daelim type intakes and tree'd them up. As I'm writing this, the wax is being cooked out of the mold in my oven. Probably this week I'll cast the mold and see if things are improving. I altered my mold design based on some suggestions from fellow engine nerd / metal caster Graham. Elsewhere, I used a bore bar to enlarge the small end on my Vespa PK crankshaft to fit the new piston for my smallframe racer. I originally bought a 20mm reamer to do this, but after setting everything up, the Adamantium or whatever the con-rod is made of actually dulled the blades on the reamer. The new piston is about 8mm wider than the old one, and should produce a big improvement in capacity.