Harley Clamping Down on Owners

[finsfanscott]

Something tells me that if your dumping exhaust out at 16 mpg you're creating more pollution than if you were getting 20 mpg, but I guess carb doesn't see it that way.

There are 3 main pollutants that the EPA measures. CO, CO2 and NOx. For gasoline engines, the most difficult one to reduce is the NOx. Air is mainly Nitrogen and Oxygen. When you burn (oxidize) fuel in a closed system, you get very high temperatures and pressures. That's what moves the cylinders. At these high temps/pressures part of the Nitrogen (normally inert or unreactive) combines with the Oxygen to produce NOx (smog). In the past, the limits were high enough for NOx that we could comply with a "lean burn" engines, a good example (if anyone remembers) is the Honda CVCC engine.

Peak engine performance (power and fuel consumption) are optimized with about 2% excess O2 in the exhaust. This means you put (a little) excess air in the cylinder to ensure all the fuel is burned. In 2dogs' example of readjusting timing and carb probably gets him to that 2% O2 level. But as we know, today's emissions controlled engines all have catalysts. Because O2 is way more reactive than the NOx that we are trying to control, all the O2 has to be out of the exhaust before it gets to the catalyst. So today's engines are set to run slightly rich, using a little more fuel than needed to ensure all the O2 is consumed. This produces a "dirtier" exhaust with more NOx that the catalyst can now clean up. This is why today's engines have O2 sensors so they can automatically vary the air fuel ratio (by varying the the amount, timing, and sometimes even the pressure of fuel injection) and the ignition timing to ensure there is almost no O2 in the exhaust. So when you remove your catalyst and don't adjust timing or air fuel ratio, you really won't get much improvement. While I don't know if this is true, but some of the companies offering to re-map your computer could be altered to allow the engine to run slightly leaner and get more power, but that would be illegal in an on road vehicle.

Hope this helps understand some of the dynamics involved and how sometimes using more fuel can result in cleaner exhaust.

[LeftCoast]

thanks, now all my high school and college chem class nightmares are reawakening. And no, I did not do well in my chem classes.

Nice explanation though!

[2dogs]

My chem class in high school was to say the least, a total waste of the teacher's time. I dropped chem class and took typing in the hopes of getting a date with one or two of the girls in that class. Little did I know typing would become a major asset in my future. Possibly the most useful class in HS. My son gave me his left over chem books from his college years which came in useful when I had to take some hazmat classes. I have see explosive, or hazardous material placards and I'd look up the number in my handy dandy reference book to find out what it was. That was the sum total of my interest in chemistry. I think I'm getting what finsfanscott is talking about. I've noticed the tail pipes on my wife's jeep are black looking and the tail pipes on my vet are a light gray color. My tail pipes are much cleaner looking than hers. Thanks to IdahoMtnSpyder and finsfanscott for the insight into info on engine combustion chemistry. Thanks guys.

[Gwolf]

Simple logic would say you're right, but like everything in life, nothing is simple. I'm no smog or chemical expert, but if CO2 and H2O were the only products of combustion we probably wouldn't have a pollution problem at all, except maybe with regard to amount of CO2 being dumped. But because of all the chemicals in the air and fuel the combustion process can get pretty complicated and changes in factors such as compression ratio and fuel to air mixture can change the output significantly. So it's all a balancing act. Remember back in the late 60's and early 70's? MPG was as low as 7 to 8 mpg for ordinary big boat cars. With the technology and understanding at that time excess fuel consumption actually reduced some recognized pollutant output levels. Higher mpg levels may result in higher toxic chemical levels while reducing CO2 and H2O.

I suspect no one yet today knows exactly what all chemicals released into the atmosphere have what kind of adverse impact on plants, animals, and humans. As that understanding evolves so does the target for emissions.

So maybe Fred Flintstone's car did kill off all the dinosaurs?

[IdahoMtnSpyder]

So maybe Fred Flintstone's car did kill off all the dinosaurs?

Probably all the dust from his feet accelerating and braking!!