Lower Emissions

Aug 08, 2011
Rating

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.

Lower Emissions

Comments for Lower Emissions

Comments for
Lower Emissions