I'm a big fan of that link. I have it saved as a tab on my iPhone's browser and check it almost every day for an update. I have to admit, though, I'm a little confused by some of his innovations. In spite of that, it's a brilliant read and gives tons of insight into the situation of two-strokes. That article (series?) is the reason I am boycotting Honda. I will never buy one of their bikes, cars, lawnmowers, etc. This is excerpted from the link toon provided. The last two paragraphs in particular almost made me throw up.
"Compared to Honda's NXR780 four-stroke twin rally race bike," said Kumli, "the EXP-2 has very similar performance, with several advantages. While the single-cylinder EXP-2 produces 54hp to the big NXR's 71hp, they both make 58 lbs-ft of torque, but the EXP-2 is 118 pounds lighter giving it a slightly better power-to-weight ratio. What all this boils down to is that the EXP-2 has about the same real-world performance as the 780, but with substantially better fuel economy and lower emissions."
[...]
Obviously, Honda had a good engineer doing good work. He had one more song to sing before the bean-counters dropped the axe on him.
He did not begin with the long-stroke CR250, but with half of Honda's NSR500V. This was a case-reed road-racing engine with a square bore-stroke ratio - like the McGrath generation YZ250s. Honda said that it made "135-plus horsepower" at 10,500 rpm; about 68-hp for a 250.
[...]
There was a rumor that the NSR500V might be turned into a killer street bike. Of course, that never happened. Instead, Ishibashi was sent off to design Civic door latches, or whatever.
[...]
About now, someone should be asking: "If Honda knew how to make two-strokes that are cleaner and more economical than their four-strokes, that do not require any new technology, and that could win endurance races, why didn't they produce them?"
Back in 1984, Steve Anderson (then Technical Editor of Cycle World Magazine) went to Japan for a VIP tour of Honda's (then) new racing R&D facility. There, Takeo Fukui, Design Director, "...made it clear that Honda views itself as a four-stroke company that will not be satisfied until it wins all of its championships with four-strokes." Simply put, the four-stroke engine has been company policy; in fact, it has been more of a religion. Anderson saw, "...shelf after shelf of oval pistons..." and was told that engines were running "...with at least eight valves per cylinder..." and turbo charging. We haven't heard anything about oval pistons in a long time because, after spending umpteen millions of dollars, somebody saw that it was a really stupid idea. It was a way of getting around the racing rules. Four-strokes couldn't win within the rules, so Honda had to find some way to beat the two-strokes and/or the rules. The trouble was, no matter what the shape of the pistons, or how many valves they could stuff in, or how many rpm they could get out of them, the two-strokes kept getting faster and the four-strokes weren't even able to keep pace. In 1995, Mick Doohan was asked how much power his NSR500 two-stroke made: "I can't tell you that, but I can tell you that if Honda produced a one-liter motor it would make upwards of 400 horsepower."
It was about that time, it seems, when one of the four-stroke monks had an epiphany: "Instead of spending more money on exotic engines," he might have said, "which hasn't been getting us anywhere, why don't we just buy the AMA and FIM and make our own rules? For instance, we could require that all two-stroke riders wear their helmets backward - if they can't find the first turn, we have to win!" And that is - sort of - what happened.
Anyway, after reading through some of Hickox' postings here, I set about thinking of a way to come up with a method for a direct-injected two-stroke that would not lose compression during scavenging. The problem with transfer ports is that you not only lose compression by air escaping out the exhaust, but you also have some sucked back into the crankcase through the transfer ports before the piston can close them off. The result is an engine with notably less compression than a naturally-aspirated four-stroke, because the cylinder is essentially leaking. I wanted to stop it leaking, and maximize compression. This would allow the engine to have just as much, if not more top-end power than it does now, while losing nothing in the bottom-end because you don't need to worry about port timing at all anymore. I also wanted to avoid having the crankcase being used in the process, because I wanted to eliminate the problem of oil coming out the exhaust.
What I did was add a pair of "charging pistons" to the system, hooked directly to the crankshaft in the same manner as the regular piston. Together, their displacement is equal to that of the piston itself. The non-cylindrical cylinders they occupy are sealed by reed valves at both ends - between the charging cylinders and the main cylinder, as well as the charging cylinders and the air filter. As the charging cylinders move down, they close the reed valves to the cylinder and open the reeds to the filter, sucking in air like a four-stroke does. At BDC, the reeds to the filter close and the reeds to the cylinder open, pumping air into the cylinder to scavenge out the exhaust. The piston then closes the exhaust valve, and begins compressing the air as it's coming in. About this time, the charging pistons are at TDC and the cylinder is sealed for compression. A lot of compression! From there, it's a simple DI system.
I'm designing this in Autodesk Inventor as a sort of really fun school project. In addition to the system described above, I've also put a Maico-style clutch on the crankshaft rather than the mainshaft. This means the clutch deals with more RPM but less torque, allowing it to be smaller and therefore lighter. I haven't even started on that yet, though. I'll post some screenshots tomorrow; I've not got time tonight. Stay tuned!
