MPGs
- Thread starter qman
- Start date
No, then I would have no reason to add useless bits of fluff to my replies.
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BakerBoy
It's all small stuff.
My 98 st11 averaged 50.3 mpg over 85 tanks, 40.4 low, 56.6 high. It had a +2" windshield, k&n air filter, otherwise stock.
My 04 st13 averages 50.3 mpg over 249 tanks, 38.2 low, 61.3 high. It is totally stock other than added fairing and mirror air deflectors.
Both bikes showed 5-10 mpg lower at lower elevations, and 2-5 mpg higher at high elevations.
My 04 st13 averages 50.3 mpg over 249 tanks, 38.2 low, 61.3 high. It is totally stock other than added fairing and mirror air deflectors.
Both bikes showed 5-10 mpg lower at lower elevations, and 2-5 mpg higher at high elevations.
That is interesting !! How do you define lower & higher elevations ??
Like John my bikes and cars get better mpg at higher elevations. So for me I live at about 6700 feet. If I ride all day at 8000 and above like John I get a few mpg better. I used to have a 2000 VW Jetta TDI I would consistently get 43 mpg when I would go to Gunnison, CO a high elevation drive I would typically get 50 to 53 mpg.
That 98 musta' been a distant twin to my 92
........+1 on the higher elev./higher mileage, lower elev./lower mileage.
BakerBoy
It's all small stuff.
There's no elevation that triggers an abrupt change in mileage--it is connected to the fact that oxygen mass per unit volume decreases with elevation, so fuel stoichiometry changes with elevation. If you live at 2000 ft elevation, you'll see higher mileage at higher altitudes from there, and lower mileage at lower altitudes.
If/when you get to Colorado, don't expect the same power output out of your ST11! It will have less power (and use less fuel). Normal.
Someone needs to put a turbocharger on their bike. That would be interesting to see how that would work in higher elevations.
If you ride at the elevations here in Colorado most of the time and them go to 1000 feet or less it is like having a turbo on the bike. Like John mentions more mpg for less HP. Somewhere in the neighborhood of 5% loss of HP per each 1000 foot rise in elevation.
This is related to what I said earlier. Change one of the design parameters and others are affected. Here we are increaseing oxygen in the air per unit volume as we go to lower elevations, increasing the power output, and decreasing the fuel economy. Adding the supercharger (or turbocharger - both do the same but get the power for the compressor differently) simply crams more air/fuel into the cylinder and ups the power. Burn more fuel, get more power, you will lose a few mpg.
An interesting manifestation of this altitude phenomenon is that small planes (normally aspirated) are more efficient the higher they fly but their engines also may put out only 50% of their sea level power at altitude. Eventually, they hit their 'ceiling' and can fly no higher. Same exact behavior as what we are talking about but presumably, planes routinely fly higher than most of us ride.
I read that a turbocharger is ideal for an airplane engine. It is desirable because it "maintains" power at higher elevations ( compared to at ground level ) , rather than increasing power at higher elevations.
For auto's , a turbo is mainly a power adder, without sacrificing mileage ( when driven for mileage ). My 1.4L Sonic w/turbo has decent acceleration for such a small engine, and I get 40 mpg on the slab.
Extra power doesn't necessarily come at the expense of higher fuel consumption, it depends on the compression ratio of the engine, higher compression is more efficient. Supercharging is another way of increasing cylinder pressure, so you end up with the efficiency of a higher compression engine, while also overcoming the effects of lower air density. The tradeoff is being able to avoid detonation as the cylinder pressure increases, but if that can be accomplished you can get more power with the same amount of fuel or less.
Back in the '80s I rebuilt a KZ1000 into an 1100, which upped the compression ratio in the process. Not only did the bike have noticeably more power, my freeway mpg went up by 5-10%.
That's turbonormalizing. I know it sounds like I made that up, but it is the legitimate description.
http://www.aopa.org/Membership/Sweeps/Previous-Sweepstakes/2001/AOPAs-2001-Bonanza-Sweepstakes-Turbonormalizing-vs-Turbocharging
On the off chance that folks are interested in a little more trivia:
For normally aspirated piston aircraft, power drops off with altitude, but so does the difference between indicated airspeed (determined by pitot - static pressure differential) and true airspeed (actual speed of aircraft within the airmass it is traveling). For general light aircraft, it is pretty much the indicated airspeed that governs how the aircraft flies, while it's the true airspeed (that's ground speed in still air) that generally gets you to your destination quicker. The happy zone usually occurs around 7500 feet MSL where you can run full open throttle so pumping efficiency is higher, you generate ~75% power where the motor is happy, and with leaning, you get good true airspeed for fuel consumed along with not needing supplemental oxygen and it's usually not too darn cold. In fact 7000' is often comfy in summertime due to the normal temperature lapse of about 4F per 1000 foot. ie - 28F cooler than on the ground. "Climb and miantain 70 degrees Fahrenheit."
Turbonormalizing allows you to retain higher power availability at higher altitudes, so climb performance doesn't tank so badly and you can cruise quicker and higher. However, you still need to respect the engine's stress tolerance and heat rejection capability so prolonged operation above certain manifold pressures is not good. One benefit of turbonormalizing compared to turbocharging (to a higher than standard sea level pressure) is the a turbonormalizer installation does not stress much of the power train over the core engine's capability; though it does add extra heat in certain areas. All these things are well documented in various charts and placards on the aircraft or in the Pilots Operating Handbook. Some are available online for browsing.