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Old 10-03-2011, 11:00 AM   #331 (permalink)
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Streamlining a Ninja 250 - continued

We have completed the body structure on Alan's Ninja. It definitely holds four bags of groceries. The framework is very strong and the entire assembly comes off with three fasteners.

We are going slow... working off a centerline for accuracy... taking our time. Next, we apply the skin. We want this bike to be ready for the trial Challenge between Las Vegas and Barstow November 20.

I need to see if the route would be appropriate for a Challenge. I have been advised that they drive way beyond the posted limits, which would not be good. We'll see. Anybody care to join us?

Craig

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Old 10-03-2011, 01:30 PM   #332 (permalink)
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Craig,
I lived in Barstow for a few years and traveled to Vegas several times. Yes, speeds are regularly 80+ mph. Slowing to 70 mph puts you solidly in the slow lane.

This would be, however an excellent test bed for the high speed stability of aerodynamic improvements. Winds can vary alot from headwinds, sidewinds and tailwinds and can be pretty strong too. There is a pretty steep pass in there between Baker and Stateline that will tax horsepower, especially with a headwind. I dare say this stretch of road is probably one of the most demanding higher speed roads in America, especially on a 120 degree summer day, and that horrible stuff they call gasoline in California.
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Old 10-03-2011, 01:53 PM   #333 (permalink)
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Thanks for your insight. I know that my streamlined Helix won't go 80 mph up those hills. But I'll bet the streamlined 250 Ninja will. That thing is fast! And, he always burns a little less fuel than I do. Maybe a lot less with his Vetter Streamliner Kit installed.

We will be departing the Red Rock Casino November 20, 2011 at 9 am. Things could be worse. (It could be in the awful heat of summer.) I expect this to be a very informative test of real mileage in "Real American riding."

It would be a great Annual Final Challenge wouldn't it?

We'll see.

PS... The good news is that we will be able to fill up with Nevada gas
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Old 10-03-2011, 02:19 PM   #334 (permalink)
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Gearing and efficiency

Quote:
Originally Posted by alvaro84 View Post
That might be true, yet it's probably a very bad idea to cruise at that rpm: an 1200cc bike engine at 4200rpm needs ridiculously light throttle which gives very bad efficiency, even if the engine could theoretically do its best there. (May not be true at 90mph anymore, but most of its energy will be absorbed by the aero drag then, so it'll be inefficient again.)

Having it spin slower can mean a higher load which, eventually, almost surely leads to much better efficiency.
"Efficiency" can mean many things. It depends on how it's defined

To a racer it can mean how much power can this thing put out, measured in horsepower. It can also mean how full can the cylinder be filled on each stroke, measured in maximum torque. It could also be defined as the area under the torque curve that shows how full the cylinder fills over a useable or defined RPM range. All of these are measured at full throttle, meaning there is little restriction in the intake system. We usually don't ride full throttle for extened periods on the street and expect fuel efficiency so these numbers probably don't apply for our purposes.

Efficiency is also expressed as BSFC or Brake Specific Fuel Consumption. Gasoline ICE engines are most fuel efficient where BSFC is lowest. This can occur at RPM and load points other than the torque maximum (at WOT), usually at a lower RPM than the torque peak, that I've seen. The BSFC chart also considers less than maximum throttle openings so it's directly applicable to real-world loads, not WOT maximum outputs. A small engine running at high RPM and WOT producing 20hp is not always more efficient than a larger engine running slower and producing 20hp. There are factors of mechanical friction at high RPM for the small engine and the energy required to overcome throttling loss at less than WOT for the big engine. Then there is the efficiency of the combustion event itsself.

To manage these factors for the maximum fuel efficiency possible while producing ONLY the power required there is a balance to be found having:
a) a wide throttle opening to reduce throttling loss (tall gearing)
b) a low RPM to reduce mechanical friction
c) an efficient combustion event to completely burn the mixture

Finding an engine with the smallest BSFC for the power required will get you the highest fuel efficiency. Simply operating the engine you have at it's lowest BSFC will maximize your efficiency as we define it. Finding the BSFC for your engine is elusive though.

I suspect the Harley in question has maximum torque (cylinder filling efficiency) at 4200 rpm. Alvaro and most of the rest of us efficiency geeks define efficiency as how much fuel is used to actually propel the vehicle at a given speed.

There are other factors as well, most of which is aerodynamic drag over about 50mph or so.
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Old 10-03-2011, 05:23 PM   #335 (permalink)
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Quote:
Originally Posted by beatr911 View Post
"Efficiency" can mean many things. It depends on how it's defined

To a racer it can mean how much power can this thing put out, measured in horsepower. It can also mean how full can the cylinder be filled on each stroke, measured in maximum torque. It could also be defined as the area under the torque curve that shows how full the cylinder fills over a useable or defined RPM range. All of these are measured at full throttle, meaning there is little restriction in the intake system. We usually don't ride full throttle for extened periods on the street and expect fuel efficiency so these numbers probably don't apply for our purposes.
Actually, it isn't...

Plain and simple, efficiency is a ratio of output to input. Horsepower and torque don't describe a ratio, and thus aren't efficiency ratings. In general, increasing volumetric efficiency will increase horsepower and torque, but that doesn't mean the latter are efficiencies.

BSFC is a measure of efficiency since it is a ratio of output (brake power) to input (fuel consumption).
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Old 10-03-2011, 06:33 PM   #336 (permalink)
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I admit that I do not understand much of what you are talking about. To win a Vetter Fuel Economy Challenge, you simply need to consume the least energy in dollars and cents.

Craig
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Old 10-03-2011, 07:33 PM   #337 (permalink)
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you imply there are no other rules... And I'm not sure they were discussing vetter competitions.

BTW, re: efficiency, from an eco perspective I think it is safe to assume an unqualified comment about efficiency relates to fuel efficiency, since that phrase appears more often than any other by a wide margin here.
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Old 10-03-2011, 10:14 PM   #338 (permalink)
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Quote:
Originally Posted by darcane View Post
Actually, it isn't...

Plain and simple, efficiency is a ratio of output to input. Horsepower and torque don't describe a ratio, and thus aren't efficiency ratings. In general, increasing volumetric efficiency will increase horsepower and torque, but that doesn't mean the latter are efficiencies.

BSFC is a measure of efficiency since it is a ratio of output (brake power) to input (fuel consumption).
Power = work/time, a ratio
Torque = force x moment arm, not a ratio
BSFC = fuel used/torque, if I am not mistaken, a ratio

The word "efficience" is a catch all for everything good in society... and as you suggest it is too often misused.

For us the ratio is Fuel Economy = distance traveled/volume fuel consumed, a ratio

For Craig Vetter the ratio is Economy = $ for fuel/distance traveled...

Last edited by redyaris; 10-03-2011 at 10:34 PM..
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Old 10-03-2011, 10:41 PM   #339 (permalink)
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well it is still a lot about $ here too, but that is achieved through efficiency (preferably in a cost effective manner). The cost of gas makes a poor basis for efficiency comparison on even a daily basis and zip code to zip code basis, but gallons and liters are readily understood across time and space.
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Old 10-03-2011, 10:49 PM   #340 (permalink)
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Considering all the different kinds of fuel... Gasoline, Diesel, direct sun, wood, coal, natural gas, nukes, etc etc... isn't cost a good way to measure?

It only becomes difficult if the government has meddled... subsidizing... depletion allowances... applying road taxes... not applying road taxes...

They wouldn't do that, would they?

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