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Higher RPMs netting better MPG, WHY???

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Ghost Rider

Ghost Rider

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My current scoot is a 2011 Ninja 1000 (SX1000). It's not a race replica, but rather a more commuter friendly motorcycle. The machine redlines at 10K and I've notice that when I ride with the RPMs in the mid-range of 5k-5.5k, I'm getting better gas milage than when using top gear and keeping the revs closer to 4K. It seems counter intuitive to run more RPMs and get a better return of MPG. 6k RPMs at 86 MPH is better gas milage compared to 55MPH at 4K RPMs. Take it past 6K and you see significantly diminished returns for fuel mileage, but not smiles per mile.

SO... What about the fuel mapping or other aspect of a machine would make it so much more efficient with increased RPMs, rather than sort of loping along. The difference between running at 4K and 5-6K is about 3-4 more MPG in favor of higher revs.
 
maybe in a better power range for efficient operation so the engine is not struggling to keep moving and needing less fuel.
 
Lower RPM's doesn't always mean more efficient. Every engine has a sweet spot where RPM's, fueling and gear ratios coincide to make a bike really sing. Anecdotally, I feel like it is near where horsepower and torque cross on the dyno on most bikes.
 
My guess would be that it has alot more to do with your riding inputs that the bike's RPM. At 4K when you need to make a move, change lanes, pass, whatever; you have to give the bike a heavier throttle input. At lower RPMs at well in a higher gear fueling on FI bikes tend to be a little rich. The higher RPM allows finer/less inputs.
 
Yep, every engine has it's sweet spot. Take it to extremes and it may make more sense:

Ride at 30mph - hold that speed in each gear. You'll find that 1st gear is revving absurdly high, so it is fairly easy to see that even if you aren't putting much fuel in with each revolution, there's a bunch of revolutions happening, and the fuel will be dropping.

2nd or 3rd (not sure about your particular bike) will feel pretty comfortable, but will still have lots of power left to accellerate, and the throttle will be only slightly open, so you have reduced your RPM significantly from first gear, and you aren't dumping much fuel per revolution either, so you're getting significantly better mileage than 1st gear.

Top gear will be on the low end of the RPM range, and even though it may not be low enough that the bike bucks or obviously lags, the bike will be noticeably less responsive to throttle, and the throttle opening required to maintain speed will be more than on the 2nd/3rd gear run. Your # of revolutions has gone down, but you are dumping more fuel and air in each revolution. (and generally the mixture gets richer with throttle opening as well, so not only more fuel/air combo in each revolution, but the fuel/air combo has more fuel than before). So the reduction in RPM is outweighed by the increased throttle opening required..


In other words, don't think of it as strictly RPM, but a combination of RPM and throttle opening. You want the lowest RPM combined with the lowest throttle opening (in general).
 
I knew we had a sharp group of folks. Thanks for the input. I'll take note of the comments and put them into practice as I watch my throttle position.
 
mmmmm I think there maybe a problem with your numbers.
a popular mod of owners of Z1000SX is to go up one tooth on the counter shaft sprocket to lower cruising RPMs and they report no real detectable effect on fuel economy and performance little effected but the reduced RPM reduces buzz.

the ninja turns higher rpm than any other comparable bike at any speed.
enough that many people keep looking for another gear.
 
Howdy! I noticed the same thing with my truck. If I'm cruising around the 50-60mph range, I can sometimes get better mpg if I drop a gear.
 
IndyRC said:
Howdy! I noticed the same thing with my truck. If I'm cruising around the 50-60mph range, I can sometimes get better mpg if I drop a gear.
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if it is a chevy with the V-6 they have way to much over drive. we had a 05 chevy at work and over drive dropped the RPM to the basement well below the torque band and it would struggle to pull. pull the lever down to D and it was much happier.
 
My Super Tenere has an instant and average mpg readout. My best instant mileage, 70 mpg, is loafing along at 45 (~2200 rpm) in six gear. Air and rolling resistance is low, air pumping losses through the throttle body and piston sliding friction are also low. I've explored this while my fuel indicator was blinking and the next gas was miles down the road.

Going up hill against a head wind at 80 it drops to 28 mpg. My average mileage on hard runs will be 40, less than 70 will be 45.

Many variables but ignition advance, cam timing, intake runners optimized for higher rpms, fueling at different rpms could be a factor. Enjoy your increased mileage.
 
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Ghost Rider said:
My current scoot is a 2011 Ninja 1000 (SX1000). It's not a race replica, but rather a more commuter friendly motorcycle. The machine redlines at 10K and I've notice that when I ride with the RPMs in the mid-range of 5k-5.5k, I'm getting better gas milage than when using top gear and keeping the revs closer to 4K. It seems counter intuitive to run more RPMs and get a better return of MPG. 6k RPMs at 86 MPH is better gas milage compared to 55MPH at 4K RPMs. Take it past 6K and you see significantly diminished returns for fuel mileage, but not smiles per mile.

SO... What about the fuel mapping or other aspect of a machine would make it so much more efficient with increased RPMs, rather than sort of loping along. The difference between running at 4K and 5-6K is about 3-4 more MPG in favor of higher revs.
Click to expand...

Yur test must be flawed. Maybe you were going uphill when riding at lower RPM. Maybe there's more head wind. Maybe you just had a feast. Maybe the pump at the gas station is wrong, or there's no ethanol in it than usual. Etc.

RPM is inversely proportional to MPG.

I think your 3/4 MPG loss/gain is just normal variation.
 
TwoSmokeDS said:
Yur test must be flawed. Maybe you were going uphill when riding at lower RPM. Maybe there's more head wind. Maybe you just had a feast. Maybe the pump at the gas station is wrong, or there's no ethanol in it than usual. Etc.



RPM is inversely proportional to MPG.
Click to expand...


[ame="http://youtu.be/Txta4uThApE"]South Park Mr Mackey mmkay - YouTube[/ame]



Signatures ???? We don't need no stinking signatures !!!!!
 
TwoSmokeDS said:
Yur test must be flawed. Maybe you were going uphill when riding at lower RPM. Maybe there's more head wind. Maybe you just had a feast. Maybe the pump at the gas station is wrong, or there's no ethanol in it than usual. Etc.

RPM is inversely proportional to MPG.

I think your 3/4 MPG loss/gain is just normal variation.
Click to expand...

Wrong. Way, way, wrong. Two years of dyno and application testing dozens of vehicles ranging from a 50cc moped to a semi with 1600lbs/ft of torque on a variety of bio-fuels says you're wrong.

Summing it up, fuel efficiency is a function of speed and throttle position. The higher the speed without changing throttle position, the better the economy. The closer to closed the throttle position without changing speed the better the economy. Almost all passenger vehicles and light trucks are geared to excel on the EPA's emission tests which is lugging the engine in most practical applications. Most modern vehicles would return better efficiency if their final drives were actually lower, though the mandated fleet fuel efficiency standards have brought final drives down a bit.

Tdub has been fitted with a plethora of devices for measuring all kinds of variables, and with the dyno set at 50mph WOT in 5th, a downshift to 4th needed only about 3/4 throttle to generate the same torque at 50mph, with a corresponding 19% decrease in fuel flow. Yes, we were measuring actual fuel flow rates, wheel speeds, and torque. We were also measuring unburned hydrocarbons, which fell dramatically when downshifted. The carb was properly tuned.
 
So you are saying all these squids running around on the highway with no muffler in second gear engine screaming at 8000 rpm, are actually being smart and getting crazy high fuel economy?


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focus frenzy said:
So you are saying all these squids running around on the highway with no muffler in second gear engine screaming at 8000 rpm, are actually being smart and getting crazy high fuel economy?


Sent from my iPhone using Tapatalk - now Free
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Well, if that's what you want to believe. :rolleyes:
 
i'm gonna engineer this crap a little bit... SO this may be why as well.

Usually an engine's power curve is pretty much linear. AKA you gain horsepower linearly as RPMs increase. If your bike has a non-linear power curve, then horsepower likely increases more than a linear power curve. IE LINEAR: 2000 RPM 20hp --- 3000 RPM 30 hp --- 6000RPM 60 HP

Non-linear is like 2000 RPM 20 hp ---- 3000 RPM 35 HP ---- 6000 RPM 75HP

Also, I'm assuming that an engine at higher RPMS runs overall more efficient than at lower RPMs. By efficient i mean, more hp vs the amount of gasoline used.

SO... now aerodynmics come into play. As a really good example I found out with my Dorsoduro recently. My dorso has instantaneous MPG calculation. I find that I get about 6-8 mpg MORE when i have a tail wind at highway speeds. Drag from wind/air is increased non-linearly with speed. IE drag actually increases with a Velocity^2 term. So say drag at 20mph is 20 lbs then drag at 40 mph would be like 60lbs and so on.

So now something else comes into play. You have geared the engine lower. So.... a lower gear puts less work on the engine to fight drag AND increases RPM which increases engine efficiency (due to a non-linear power curve).

So all these factors come into play. And more than with a car/truck because a motorcycle has a much lower hp vs drag ratio than a regular vehicle (at highway speeds).

I hedge my bet that you had tail winds/head winds messing with you a bit.

ALSO this can be proven via youtube. Theres some drag race videos of bikes vs vehicles. Watched a video of a GSXR1000 vs a 700hp Toyota Supra. After about 120mph the supra pulled past the GSXR. WHy? The supra has a much better hp vs drag ratio than the motorcycle. GSXR has plenty of power to weight vs the car but at higher speeds drag takes over.

I have a Bachelor's of Science in Mechanical Engineering from Penn State.
 
Oh, goody, an engineer! Please explain the relationship between volumetric efficiency and fuel mileage.
 
RadicalTireSkid said:
i'm gonna engineer this crap a little bit... SO this may be why as well.

Usually an engine's power curve is pretty much linear. AKA you gain horsepower linearly as RPMs increase. If your bike has a non-linear power curve, then horsepower likely increases more than a linear power curve. IE LINEAR: 2000 RPM 20hp --- 3000 RPM 30 hp --- 6000RPM 60 HP

Non-linear is like 2000 RPM 20 hp ---- 3000 RPM 35 HP ---- 6000 RPM 75HP

Also, I'm assuming that an engine at higher RPMS runs overall more efficient than at lower RPMs. By efficient i mean, more hp vs the amount of gasoline used.

SO... now aerodynmics come into play. As a really good example I found out with my Dorsoduro recently. My dorso has instantaneous MPG calculation. I find that I get about 6-8 mpg MORE when i have a tail wind at highway speeds. Drag from wind/air is increased non-linearly with speed. IE drag actually increases with a Velocity^2 term. So say drag at 20mph is 20 lbs then drag at 40 mph would be like 60lbs and so on.

So now something else comes into play. You have geared the engine lower. So.... a lower gear puts less work on the engine to fight drag AND increases RPM which increases engine efficiency (due to a non-linear power curve).

So all these factors come into play. And more than with a car/truck because a motorcycle has a much lower hp vs drag ratio than a regular vehicle (at highway speeds).

I hedge my bet that you had tail winds/head winds messing with you a bit.

ALSO this can be proven via youtube. Theres some drag race videos of bikes vs vehicles. Watched a video of a GSXR1000 vs a 700hp Toyota Supra. After about 120mph the supra pulled past the GSXR. WHy? The supra has a much better hp vs drag ratio than the motorcycle. GSXR has plenty of power to weight vs the car but at higher speeds drag takes over.

I have a Bachelor's of Science in Mechanical Engineering from Penn State.
Click to expand...

ARRRRGH!
head-explode.gif


Hey man, it's Saturday!​
 
KenH said:
Oh, goody, an engineer! Please explain the relationship between volumetric efficiency and fuel mileage.
Click to expand...

i have no idea what volumetric efficiency is. I feel like its made up.


Why are you guys bashing me either way? never said you're wrong.
 
"Volumetric efficiency in the internal combustion engine design refers to the efficiency with which the engine can move the charge into and out of the cylinders. More specifically, volumetric efficiency is a ratio (or percentage) of the quantity of air that is trapped by the cylinder during induction over the swept volume of the cylinder under static conditions. Volumetric Efficiency can be improved in a number of ways, most effectively this can be achieved by compressing the induction charge (forced induction) or by aggressive cam phasing in naturally aspirated engines as seen in racing applications. In the case of forced induction volumetric efficiency can exceed 100%." Wiki... so it's gotta be true.

While not "made up", not quite on target for the discusssion. What I have noticed from earlier in the thread is that loping the engine along is not netting the same level of MPG as picking up the RPMs. The significant decrease of MPG when turning 6K RPM at 86 MPH is probably where wind resistance become significantly harder for the machine to overcome. I could tuck behind the wind screen to eek out another couple of MPG, but I'd pay for in Chiropractic bills; so no savings there. From just being mindful of my throttle position, I noticed an increase of fuel milage. Will report back with more info after the next set of commutes.
 
After six years of owning bikes, and half a lifetime of riding them, I can report that the best mpg is achieved when you don't care about mpg.

YMMV, of course. ;)
 
not sure what the "charge" is.
Based on that explanation, I guess its the efficiency of an engine to run clean air during every cycle. So engines may not release 100% of the exhaust gas in the exhaust stroke and then in turn only let in less than 100% of the volume of the cylinder on the intake stroke. Wierd I had 2 I.C. engine classes and never heard that term or at least don't remember it. Whatevs.

Went for another ride this morning. So, again with the instant MPG stuff. I drafted a lincoln navigator (huge SUV) for like 3 miles or my dorso. Gas mileage at 80mph was 54mpg believe it or not. Lose the draft and im down to 44-46 mpg. Also drafted a rig at 70 mph, this time about 60mpg. Drafting is sweet but yea dangerous.
 
Idk about your bike, but the instant mpg on my car is wildly off.
 
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