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QUOTE=darcane;261151]The premise seems to be testing whether cars or bikes produce lower emissions (I presume this is a question because bikes have better mpg but less pollution controls). Looks like they put it to an "ultimate" test by streamlining a bike.[/QUOTE]
Mythbusters can be fun to watch once in a great while, but their science is often deeply flawed, and half the stuff they do can be answered without the theater and within a minute on the web.
Bikes emit far more criteria emissions than cars, because they are allowed to do so. (There are not as many bikes; it's harder to clean up a high-specific-output-engine; some of the manufacturers are small and would be burdened; etc.) Ironically, the fastest bikes now owe part of their speed to technologies that came from the implementation of emission controls in cars.
It used to be true to say "A Jet Ski emits more pollution in and hour of operation that a Volvo emits in an entire year." The differences in emission standards are narrowing, but a 50cc scooter is allowed to emit on the order of 10 - 50 times as much (measured in grams per mile) as a 7 series BMW. All cars have to meet one regulation; bikes have three levels, with bigger bikes required to emit less (even though they obviously burn more fuel).
So if you streamline a bike to get 150 mpg, The bike will still emit more criteria emissions than any car... even the very biggest, heaviest gas guzzlers.
However, CO2 is now considered a "pollutant" but is not regulated. In this sense, a 150 mpg motorcycle emits one third the CO2 of a Prius. (CO2 is not only conveniently tied to MPG, it is actually the thing measured in EPA dyno tests to indicate fuel burned.) (I used to use a pipette when I ran motorcycle dynos in the dark ages.) CO2 is probably more important these days. The criteria emissions are easy to deal with -- they are all but eliminated in cars (and bikes could be equally clean if we wanted to make them so). But CO2 is nearly impossible to deal with -- none of the sequestration methods seem to be likely to work well.
So today, knowing what we do, it is probably better to get 150 mpg in a streamlined bike than to get 50 mpg in a Prius with one person in it. Doesn't really mater what the criteria emissions are, unless bikes get to be a significant part of the whole.
The Montracer gets 53 mpg at a constant 75 mph, and emits fra more criteria emissions than a Prius in the process. This is about equivalent to 53 mpg in an EPA highway fuel test cycle. So getting 150 mpg in a streamlined motorcycle is more than a no-brainer -- and some claims are not measured in accordance with the EPA test cycle.
Having built a tiny enclosed motorcycle, I can say it is not easy to get over 100 (real) mpg in anything that most people will want to ride.
BSFC remains a challenge, as the Monotracer shows. If you have produced a bike that requires only 10 hp to maintain 75, then a 100 hp bike engine is far too large, and engine operating efficiency might be 8%. Make the engine 10 hp, and then acceleration is rotten (and top speed is 75) -- but you've bumped the engine efficiency back up to 25%.
No free lunches today.
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