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Old 04-30-2011, 11:07 AM   #1
BloodRedSandman
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Default Getting bad gas mileage. Is this normal?

Hey guys I got an 03 CBR 600RR. Mods include a power commander, Two brothers slip on or full exhaust (IDK, can someone tell me how to find out) K&N air filter, GPR stabalizer, bigger rear sprocket or whatever. etc. Anyway my bike is my main commuter to school and work. about 20 miles of city driving per day. Stop light to stop light, crappy traffic and all that, but anyway I filled up about a week ago and reseted my odo to 0. I put exactly 3.5 gallons of regular 87 octane for like $15 and ldidnt last long. I checked today and my gas bar only had one bar left and my ODO is at like 102 miles. So its pretty much like 29MPG! I dont even ride hard nor redline the bike! I shift at about 4 - 5k and mostly cruise at 6th gear but if I pass I do pull back the throttle. Anyway is this normal? I read on some forums that you get more MPG if you put 91 octane but that doesent make sense to me. Also if I take off the PC and convert my sprocket to stock how much MPG will I get out of it? Also whats the best sprocket size for better gas mileage.
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Old 04-30-2011, 12:10 PM   #2
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Default Re: Getting bad gas mileage. Is this normal?

Go refill your tank to the top and see how many gallons you've actually used before you start freaking out too much.

Also, some power commanders are set up to run ultra rich, and use a ton of fuel.
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Old 04-30-2011, 01:09 PM   #3
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Default Re: Getting bad gas mileage. Is this normal?

If you have a CBR, you REALLY should put 91 octane fuel in your motorcycle. These Honda 600s have at the least a 12:1 compression ratio!
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Old 04-30-2011, 02:36 PM   #4
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Default Re: Getting bad gas mileage. Is this normal?

Our bikes have 12:1 and there's no need to run anything higher than 87.

You have a super sport with a lot of mods that lead to crappy gas mileage. In stop and go traffic 29 mpg doesn't really surprise me.
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Old 04-30-2011, 03:44 PM   #5
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Default Re: Getting bad gas mileage. Is this normal?

Go back to stock gearing if you're above 50 much if you really want to get the most. But yeah, fill up to the neck every time and figure out exactly what's going on. It's probably a slip-on. Not too many people splurge on a full system unless they buy it in a kit. If it is just a slip on, get a stock air filter and pull the power commander and that will probably help, or switch it to a leaner base map.
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Quote:
Originally Posted by carlitos_92 View Post
Dude. You could say your mom has a dismal power/weight ratio, but I ride her year-round, too.
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Old 04-30-2011, 05:46 PM   #6
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Default Re: Getting bad gas mileage. Is this normal?

I used to get 52mpg highway, 42mpg mixed City and Highway. Add Jet Kit with Micron exhaust and drop to 44mpg highway, 38 mpg mixed city and highway. Change to 39 tooth sprocket... same mileage ??? WTF. Figured Id get a 7th gear and save on gas. Well, it seems miles traveled are reduced by 10% because of 39 tooth gear, a 20 mile trip now registers 18 miles on the speedo. BUT if I use top gear on the freeway and not go over 65 mph I get 52 mpg. Go figure.

With addition of 39 tooth, transition between first and second and downshifting is greatly improved for everyday driving, but not for the speed racer or the track.

Last edited by Billy from Philly; 04-30-2011 at 05:49 PM.
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Old 04-30-2011, 07:50 PM   #7
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Default Re: Getting bad gas mileage. Is this normal?

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Originally Posted by bokeh View Post
If you have a CBR, you REALLY should put 91 octane fuel in your motorcycle. These Honda 600s have at the least a 12:1 compression ratio!
Uh, no. That would make the mileage worse, anyway.

http://www.cbr600rr.com/forum/index....c,18413.0.html

Quote:
Originally Posted by JHenley17 View Post
Go back to stock gearing if you're above 50 much if you really want to get the most. But yeah, fill up to the neck every time and figure out exactly what's going on. It's probably a slip-on. Not too many people splurge on a full system unless they buy it in a kit. If it is just a slip on, get a stock air filter and pull the power commander and that will probably help, or switch it to a leaner base map.
What he said. You have a bike that has been modded fairly heavily for performance, without regard for mileage. The good news is that it's reversible. Good luck.
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Old 04-30-2011, 09:07 PM   #8
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Default Re: Getting bad gas mileage. Is this normal?

Did I miss something? Who buys a CBR to commute and get good fuel economy?

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Old 04-30-2011, 10:42 PM   #9
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Default Re: Getting bad gas mileage. Is this normal?

I'm no expert on fuels, but I would like to share some things I do know:

HEATING VALUE OF THE FUEL: The power produced by any given engine in a set configuration (set cam timing, set point of ignition, set carburetor jetting, etc.), is determined by the amount of fuel put through it (per minute, or whatever), the heating value of the fuel, and the efficiency of the combustion process producing the expanding gases driving the piston down its cylinder. All other things being equal, the torque produced is (approximately) directly proportional to the heating value of the fuel. The same is generally true for gas mileage.

The heating value of gasoline is in the neighborhood of 120,000 Btu/Gal. Whether it is 87 octane, or 93 octane, the heating value is in that same neighborhood. While the higher octane* blends could be lower in heating value than lower octane blends, it doesn't have to be the case. In any case, the difference would likely be a small percentage. As stated in a previous post, running higher octane than necessary could produce less horespower, and inferior gas mileage, but not necessarily, and the differences should only be measurable with the engine on a test bed running controlled tests.

GASOLINE WITH ETHANOL ADDED: The heating value of ethanol is only around 75,000 Btu/Gal. When pump gas is 10% ethanol, the heating value of the blend drops to around 115,600 Btu/Gal. Expect power and gas mileage to be 3.7% less than with pure gasoline.

RACING FUELS: I have not conducted the research (if only because I never expect to use one), but when I asked my cousin, a retired senior chemical engineer at Chevron Research, what might be the formula for a racing gasoline, he suggested: probably higher octane, of course, because then all of the customers at the track could use the same fuel, however the manufacturer could produce racing gasoline in multiple grades. The Cuz imagines the racing gasoline blend first of all is free of ethanol, duh. He also speculates the gasoline blend might contain a higher percentage of the shorter-chain hydrocarbon molecules such as butane, pentane and hexane and less of the longer chain hydrocarbons, which have a lower heating value. He imagines the possibility of producing a gasoline of as much as 130,000 Btu/Gal or more. If so, more power for any particular carburetor jetting.

SPROCKET SIZE: The effect of the number of teeth on the rear sprocket on gas mileage only pertains to riding in sixth gear. In sixth gear, either could be better, but the smaller sprocket could be expected to win out the majority of the time, producing better gas mileage. Around town, in gears 1-5, you might be in a different gear through any section of the same ride depending on the sprocket size, and either a larger or a smaller sprocket could be the winner for that portion of travel. Different streets, different speeds, uphill, downhill... it's too complex to evaluate. And not really worth evaluating. Based on the heating value of gasoline (its energy content), it should take around the same quantity of gasoline (in gears 1-5) to propel yours and the weight of the bike, at the same speed, from here to there - same amount of energy required. Choose a rear sprocket for the performance you want. If you want high gas mileage, buy a 50cc scooter, eh?

*note from second paragraph: the reference is to "octane rating," not the actual percentage of octane molecules in the blend.
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Old 05-01-2011, 11:10 AM   #10
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Default Re: Getting bad gas mileage. Is this normal?

Yeah this has been a really heated debate man! I still put 87 but sometimes I am thinking of putting maybe 91? IDK man.
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Old 05-01-2011, 01:37 PM   #11
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Default Re: Getting bad gas mileage. Is this normal?

Ugh. Your engine was designed specifically for one octane rating. Find the manual and run that fuel, and that fuel alone.
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Old 05-01-2011, 01:43 PM   #12
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Default Re: Getting bad gas mileage. Is this normal?

Quote:
Originally Posted by BloodRedSandman View Post
Yeah this has been a really heated debate man! I still put 87 but sometimes I am thinking of putting maybe 91? IDK man.
Ever hear of the saying "Give a man a fish, he eats for a day, teach a man to fish and he eats for a lifetime?"

Use that Google thingy, and look up octane rating, and find out what it means. Then look up articles on octane and fuel economy.

Hell, search on this site alone and you'll find those answers.


Or if that's too hard, then just drop 91 in your bike and call it a day. Makes no difference to me.
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Old 05-01-2011, 02:01 PM   #13
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Default Re: Getting bad gas mileage. Is this normal?

Quote:
Originally Posted by Lestus View Post
I'm no expert on fuels, but I would like to share some things I do know:

HEATING VALUE OF THE FUEL: The power produced by any given engine in a set configuration (set cam timing, set point of ignition, set carburetor jetting, etc.), is determined by the amount of fuel put through it (per minute, or whatever), the heating value of the fuel, and the efficiency of the combustion process producing the expanding gases driving the piston down its cylinder. All other things being equal, the torque produced is (approximately) directly proportional to the heating value of the fuel. The same is generally true for gas mileage.

The heating value of gasoline is in the neighborhood of 120,000 Btu/Gal. Whether it is 87 octane, or 93 octane, the heating value is in that same neighborhood. While the higher octane* blends could be lower in heating value than lower octane blends, it doesn't have to be the case. In any case, the difference would likely be a small percentage. As stated in a previous post, running higher octane than necessary could produce less horespower, and inferior gas mileage, but not necessarily, and the differences should only be measurable with the engine on a test bed running controlled tests.

GASOLINE WITH ETHANOL ADDED: The heating value of ethanol is only around 75,000 Btu/Gal. When pump gas is 10% ethanol, the heating value of the blend drops to around 115,600 Btu/Gal. Expect power and gas mileage to be 3.7% less than with pure gasoline.

RACING FUELS: I have not conducted the research (if only because I never expect to use one), but when I asked my cousin, a retired senior chemical engineer at Chevron Research, what might be the formula for a racing gasoline, he suggested: probably higher octane, of course, because then all of the customers at the track could use the same fuel, however the manufacturer could produce racing gasoline in multiple grades. The Cuz imagines the racing gasoline blend first of all is free of ethanol, duh. He also speculates the gasoline blend might contain a higher percentage of the shorter-chain hydrocarbon molecules such as butane, pentane and hexane and less of the longer chain hydrocarbons, which have a lower heating value. He imagines the possibility of producing a gasoline of as much as 130,000 Btu/Gal or more. If so, more power for any particular carburetor jetting.

SPROCKET SIZE: The effect of the number of teeth on the rear sprocket on gas mileage only pertains to riding in sixth gear. In sixth gear, either could be better, but the smaller sprocket could be expected to win out the majority of the time, producing better gas mileage. Around town, in gears 1-5, you might be in a different gear through any section of the same ride depending on the sprocket size, and either a larger or a smaller sprocket could be the winner for that portion of travel. Different streets, different speeds, uphill, downhill... it's too complex to evaluate. And not really worth evaluating. Based on the heating value of gasoline (its energy content), it should take around the same quantity of gasoline (in gears 1-5) to propel yours and the weight of the bike, at the same speed, from here to there - same amount of energy required. Choose a rear sprocket for the performance you want. If you want high gas mileage, buy a 50cc scooter, eh?

*note from second paragraph: the reference is to "octane rating," not the actual percentage of octane molecules in the blend.

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Old 05-04-2011, 10:49 AM   #14
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Default Re: Getting bad gas mileage. Is this normal?

The only rational for using higher octane is this--prevention of engine knock/ping/dieseling/detonation whatever you want to call it. If something is a little out of spec for timing or whatever, using higher octane gas will prevent premature ignition of the mixture in the cylinders, as the higher octane rating increases the heat/pressure required to ignite the gas.

For a low-miles, 100% in-spec 599 engine used at lower RPMs, there is no reason to use high octane gas. For a higher-mileage engine ridden at high RPMs, higher octane gas might prevent a small degree of damage to the engine, in exchange for higher price and the possibility of some power loss.

So if I know I'm going to be hooning it up, I use mid-grade. But I don't kid myself that I'm getting more power.

The real thing to watch out for is % ethanol. Hate that stuff. Avoid it if at all possible. Occasionally a gas station advertises no ethanol (like the station near Deals Gap). And the dang corn lobbyists want to increase the federal mandate for % ethanol at stations.

Last edited by Sundog; 05-04-2011 at 10:52 AM.
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Old 04-30-2017, 09:11 AM   #15
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Default Re: Getting bad gas mileage. Is this normal?

That gas gauge is very approximate. The only way to measure gas mileage is to zero one of the trip meters when you fill it up and calculate it the next time you fill up. And the only way to know with any accuracy how much gas you have/how far you can get is to zero it each time you fill up and know what your gas mileage is.
Yesterday I wanted to go to a nearby town where they have corn-free gas but the gauge was on the last bar so I didn't know if it would get there. I put 3/10 of a gallon to make sure, then after the 20 mile ride it only took a little over 3 gallons. So I had over half a gallon when I left the house and could have easily made the trip. I am zeroing trip A from now on every time I fill up, and keeping track of my mileage too so I'll always know where I'm at.
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