Mythbusters aero cycle tests

[jkv357]

Anyone see the Mythbusters show where they enclosed a Yamaha WR250 with a tube frame shell wrapped in shrinkwrap? They ran some tests to try to increase MPG, but ended-up getting about 70 MPG on their closed course. Stock it got 53 IIRC.

It was pretty crude aerodynamically. They should have done some research on LSR cycles first.

Not sure if it's a new or old show, just saw it tonight.

[Old Mechanic]

As aero is improved it will take less power for the same speed. This reduces engine efficiency, which can be offset by lowering the final drive ratio. Smaller rear sprocket would give lower revs per mile and lower manifold vacuum which would increase efficiency and mileage.

regards
Mech

[PaleMelanesian]

The shape was good, but it was too big. Air drag is cd * A (drag coefficient * area). They greatly improved cd, but added a lot of unnecessary A. A tall and skinny fairing would have produced even better results.

Good on them for testing all the exhaust gases, too. Though the bikes were more fuel efficient (and the aero bike was best of all), the other emissions (hydrocarbon, CO, NOx) were much higher - 5+ times worse.

The test looked reasonably scientific. They used an in-motion exhaust gas analyzer. They used the most popular car and bike model from the 80's, 90's and 00's (6 vehicles total). The drove the cars and bikes together on the route three separate times to eliminate variables.

[LUVMY02CREW]

I was flipping channels and saw part of this. Getting kiddos in bed didn't allow me to see the conclusion.

It looked interesting to say the least.

One thing about the testing that bothers me though...They didn't actually take the aero bike out on the exact course following the same criteria did they??? It might not have made that much of a difference, but that had to flaw the results somewhat.

Otherwise, I will have to keep my eyes open so I can catch the whole episode on rerun.

[dcb]

Originally Posted by PaleMelanesian

...Good on them for testing all the exhaust gases, too. Though the bikes were more fuel efficient (and the aero bike was best of all), the other emissions (hydrocarbon, CO, NOx) were much higher - 5+ times worse...

I don't have access to the episode in question, were the other emissions as a percentage of exhaust gas volume or absolute figures? Because a large displacement single occupant vehicle can easily put out more than 5x the exhaust volume of a small commuter bike. Heck, any engine more than 1250cc can put out more than 5x more exhaust than my 250gs.

Folks who care about the other emissions do also need to care about engine displacement (and vehicle weight/drag), no? Though I would consider retrofitting a cat converter all the same if they were available/affordable. Were any bikes fuel injected with O2 feedback? Most bikes on the road aren't yet, but might be a good "mod" if you want to put a dent in emissions too.

[dcb]

I don't pay much attention to newshiney, but apparently the epa HAS put in regulations for motorcycles and discusses fuel injection and catalytic converters and etc.

It would be good to know if the 5x by percentage of exhaust flow issue is already being corrected and how a 2010+ regulation bike would compare both in percentage and absolute pollution.

http://www.epa.gov/oms/regs/roadbike/420f03045.pdf

[PaleMelanesian]

It was a new episode last night, so likely not available elsewhere, yet.

The bikes were progressively cleaner by date - the 80's bike was the worst. The new 2010 Yamaha 250 was the cleanest bike, and proportionally cleaner with the aero fairing. That's good news. I believe it is fuel injected. Still no catalytic converter I believe, so that's where the emissions came from.

Not sure if it was by total emissions or by percent. Still, even if it was by percent it comes out as worse. At maybe 1/2 the car's fuel consumption but 5x (by percent) the emissions, that's still 2.5x total output. If it was total, that's WAY worse.

[Patrick]

Originally Posted by dcb

Were any bikes fuel injected with O2 feedback?

The "aero" bike was 250cc, fuel injected and had a catalytic converter. I don't know about O2 feedback.

[BHarvey]

A well tuned bike will output the same ppm as a car but will do it without all the emissions equipment, but this will require some dyno time to get it right.

[Old Mechanic]

My 2011 CBR250R has a cat, fuel injection, and an O2 sensor. Also has air injection for deceleration. It would be interesting to test that bike with their aero improvements. The three way cats have required O2 sensors on cars since the early 1990s as a general rule.

When they got the feedback systems working, then they increased the compression and let the cat and sensor clean up the exhaust. The trend went back to performance compared to the early cat cars that were low compression gutless dogs. Injector shut off on deceleration came at about the same time, which allowed elimination of the air injection pump.

regards
Mech