Lower Emissions

by Daniel Callaghan
(Charleston, W,Va)

Now Tim, has a catalyst been tried to lower emissions? That we have in our cars, that creates a chemical reaction to kill some pollutants? If this was used on our exhaust systems, wouldn't we lower fuel emissions, allowing us to go further with two stroke motors? We could build bikes putting out lower emissions, or make a faster bike, putting out the same emissions as a comparable 4-stroke.


Would this work?

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Aug 08, 2011
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The Cat
by: Tim Hickox

I did not say much about catalysts. We must draw a distinction between engine-emissions and tailpipe-emissions. For the sake of this discourse, I wanted to talk about engines, not what could be done to exhaust gases, which is a problem in chemistry.

Most cars today do NOT have clean engines, but rather, clean exhaust - due to very effective after-treatment. But catalysts have been used on two-strokes. The (now) old RZ350 Yamahas came with a cat. An oxidizing cat actually works better (is more efficient) on a two-stroke than a four-stroke because there is more oxygen in the two-stroke's exhaust.

From the standpoint of the government, a cat is not very good, because people can just swap the exhaust system and eliminate it - which is what many RZ350 owners very quickly did. I am now in Malaysia and I just saw a new-looking Yamaha road bike with a cat - it said so where it might have said "Four-stroke". (I think this was a 125, but it didn't say that; it was a small single.)

I will also mention that there is a two-way cat (that lowers only HC and CO2) and a three-way cat (that also lowers NOx). The latter is a much more complicated and expensive system. At this time, I don't think a three-way cat is practical for motorcycles. There is a point here: two-strokes have (engine emissions) much lower NOx emissions than four-strokes.

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