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Jim_sb
| | Posted on Tuesday, October 25, 2005 - 05:02 pm: | 
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Hello Thunderbox, I thought modern FI engines were generally set to run at roughly a 14.9 (stochiometric) ratio (rough equivalent of peak EGT). (I've heard that it varies with the fuel being used, but this is in the ballpark).
I suspect a 13.8 F/A ratio implies they are running rich of peak EGT (more fuel, less air than a stochiometric ratio) which can lead to higher CHT's, more power and higher internal cylinder pressures. Also can lead to cylinder deposits. Leaner is cleaner.
I thought that due to emissions concerns these bikes were set to run lean and clean (hence my suspicion that, like autos, they're set at 14.9 or thereabouts).
For racing it's my understanding that you want your engine producing max. power at somewhere between 75 and 200 deg. F. rich of peak EGT. For best economy something lean of peak EGT is best.
Obviously modern mapping systems can do both depending on engine rpm and throttle settings.
Just curious where the 13.8 stat came from.
If an engine is set to run at any given ratio, the FI system should be able to maintain that ratio at any altitude. Since there is less O2 at altitude by definition less power is available. Mileage would increase because of A) the engine simply can't make as much power, therefore runs in a more efficient range and B) less parasitic drag (thinner air).
Aircraft cruise more efficiently at altitude as well due to less parasitic drag and less induced drag. If you're turbocharged you can have the choice of using the same fuel (and power) as you would at sea level and going faster, or you can throttle back to the same sea level speed and burn less fuel. Or any other setting that works for your aircraft.
At least that's my understanding of such things.
Regards,
Jim in Santa Barbara |
Buelldyno_guy
| | Posted on Tuesday, October 25, 2005 - 05:06 pm: |
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Just got back from a 530 mile day with the first tanks at about 45 MPG if I keep it between 65 to 80 MPH. On the way home I twisted it a little and ran between 85 and 105 MPH, the range dropped down to 135 miles before low fuel light, then I slowed down to 55-60 and ran 15 miles before a 4 gal fill up so that makes it 37.5 MPG. I am happy with what I saw. ... Terry |
Bienhoabob
| | Posted on Tuesday, October 25, 2005 - 05:20 pm: |
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I rode a FI Road Glide, and a friend was on a FI Ultra and did a Western tour. Through the plains at sea level, both bikes were in the mid to low 40 mpg. We did about three tank fillups in the Rockies and consistently hit 58 mpg. Once I hit 61.5 mpg. Speeds were much slower in the mountains (site seeing), 45-50 mph verses 70-80 mph thru the plains. That would cause part of the increased gas mileage. Overall, less air density requires less fuel delivery, but equals less power.
CV carbs would compensate for altitude changes, similar to FI set-ups.
Thunderbox is right. |
Thunderbox
| | Posted on Tuesday, October 25, 2005 - 05:40 pm: |
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Hi Jim, actually the best air fuel ratio for power production is not 14.8 to 1 but 13.33 to 1. This is between .07 and .08 pounds of fuel for each lb of air. 14.8 is a bit on the lean side but will give you better economy. Modern engines try to get close to 14.5 for emissions and economy reasons. For power we try to get closer to 13.33 to 1. Myself I like to compromise and get about 13.8 or 14 to 1. I wasn't saying 13.8 as a matter of fact it was just a number I picked to illustrate the discussion.
Many things are not as they seem on the sites. I know you probably have read to change the main jet when a performance exhaust is put on a bike. That only alters the fuel ratio at WOT, not what you would really want. That is not the correct way to improve the performance but it is the excepted procedure for most carb tuners. So you see that just because someone said it doesn't make it correct. Just because it is in print doesn't make it right either. We must either follow someone elses lead or think it out ourselves. I follow and think, then if need be, I change my mind. Too easy. |
Branebanger
| | Posted on Tuesday, October 25, 2005 - 07:16 pm: |
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is it my imagination, or does the fuel efficiency have alot to do with how hot the engine's running? |
De50man
| | Posted on Tuesday, October 25, 2005 - 07:40 pm: |
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Fuell efficiency is affected by the heat of the engine. The heat coming from the engine heats up the air coming into the intake of the bike. Hot air is less dense than colder air, and provides less combustion power.
For instance, the volume of air can be the same, but the density of the air can be different. More oxygen means more powerful combustion, which equates to more horsepower. And say you require a given HP number to keep you at a constant speed, that HP is reached more easily when the intake air temperature is lower.
So yes, how hot the engine is running does affect fuel efficiency.
I work at Wild Boar Harley-Davidson ( Huddsonville, MI) as an Intern. And we tune all our bikes on the Dyno to a air/fuel mixture ratio of 13.2 to 1 give or take .1
I have personally been getting mid to high 40mpg, with mixed city and highway driving. Keep in mind lately it has been less than 50 degrees ( ambiant air temp). I am also running a Jardine exhaust system currently, but am waiting on my ECM and air filter. |
Blake
| | Posted on Wednesday, October 26, 2005 - 12:42 am: |
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All vehicles no matter their method of fuel delivery will achieve improved fuel mileage at higher elevations. It is not due to the thinner air affecting engine performance, thought that is indeed the case; the improved fuel mileage is due to the thinner air requiring less HP to maintain the same speed, on account of there is less aerodynamic drag.
I once achieved 73 mpg on two consecutive tankfulls traveling from Sturgis, SD, then south from Rocky Mountain National Park to New Mexico. That was on a bone stock '97 Cyclone. We were taking it real easy, cruising at around 65 to 70 mph.
At WOT I'm not sure how much effect engine temperature has on power output, but a too hot or too cold ending would be detrimental to fuel efficiency. Making the most HP is another matter entirely. In chasing peak HP racers are willing to eject a lot of unburned fuel out the exhaust. That won't do much for fuel efficiency though.  |
Coolice
| | Posted on Tuesday, November 08, 2005 - 12:59 am: |
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How about some mpg updates as the Uly's get some break in miles on them. Also with luggage installed. Anyone getting the 60mpg? My 9r with racekit gets mid 50's on the slab @ 70-80, was hoping the Uly will be close. |
Coolice
| | Posted on Sunday, November 13, 2005 - 11:33 am: |
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Still no updates on mpg? A few have to ridden enough to get a average of their fuel usage, what are you getting? And does the luggage reduce it 10% with the added wind resistance of the saddlebags? |
Dmcutter
| | Posted on Sunday, November 13, 2005 - 11:44 am: |
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Been spending most of my time above 3500 rpm, around town, and am getting fairly consistent 43-44 mpg. |
Dave
| | Posted on Sunday, November 13, 2005 - 12:07 pm: |
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I was getting 48-51 running 80 mph +/- 10 mph interstate, 2-up, and full luggage.
DAve |
Smcnamara
| | Posted on Sunday, November 13, 2005 - 12:43 pm: |
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After 6 tanks full, I'm seeing right around 45 MPG, but my riding has been pretty aggressive with lots of relatively heavy throttle use, and quite a bit of riding at 80+ MPH.
-Sean |
Rkc00
| | Posted on Sunday, November 13, 2005 - 01:17 pm: |
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The last 4 tanks I am only getting 40 MPH around town. I have 2100 miles on mine now. The best I have done is 48 MPG on the highway at 70-80 MPH speed. |
Two_buells
| | Posted on Sunday, November 13, 2005 - 11:06 pm: |
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I did a hwy trip to my sister house in New Jersey
153 miles away.
On the trip home I ran to 169 miles than the low fuel light came on and ran another 22 miles before I filled up. So 200 miles on a tank full is not out of the question....
My low fuel light comes on around 150 miles during my daily ride to work...no hwy |
Jim_sb
| | Posted on Sunday, November 13, 2005 - 11:33 pm: |
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My break-in mileage was in the 45mpg range.
I went out with some friends on a 450 mile ride today. On the "good stuff".
Put the new saddlebags on last night too (but haven't done the top case yet).
Anyway, I was only 30 miles shy of 500 when I left the house this morning, so once I finally got past 500 miles I could let the bike run a bit.
IIRC my mileage today by tank was 44, 40 and 47.
On the final tank I hit 165 miles and the Low Fuel light was still dark. Definitely closing in on possibly getting 200 miles per tank.
Jim in Santa Barbara |
2hogs
| | Posted on Monday, November 14, 2005 - 06:54 pm: |
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I have 2300 miles now and consistently get 50mpg during my 100 mile (round trip commute).
This is with a light hand on the throttle. I got 43mpg last weekend while hitting the local back roads pretty hard.
Cheers |
Electraglider_1997
| | Posted on Monday, November 14, 2005 - 07:56 pm: |
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Is that 50mpg figured with optimistic speedo/odometer readings? The only reason is that if your speedo is reading 60 and your are only going 57 then your odometer will read 60 when you've only gone 57 miles. This would in turn give you higher than actual mpg. |
Stevem123
| | Posted on Monday, November 14, 2005 - 09:02 pm: |
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The accuracy of the speedometers is non linear due to being both analog and electric. At midrange they are quite accurate and only lose accuracy at the upper end of the speedometer ranges. Fuel economy and accurate MPG measurements will vary greatly depending on your riding style.
BC Steve |
Lovehamr
| | Posted on Monday, November 14, 2005 - 09:32 pm: |
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I have to disagree on the speedo accuracy thing. My speedo is always optimistic about my speed to the tune of 2-4 MPH depending on the speed measured. Just in case you're wondering these measurements are with calibrated traffic radars and are really beyond rebuke. Now this doesn’t mean that mine is the same as everyone else’s, so take that info with a grain of salt and do your own measurements before assuming that yours is just like mine. |
Jim_sb
| | Posted on Monday, November 14, 2005 - 11:13 pm: |
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2mph? Do you guys really look at it that closely?
Man, y'all behave really nicely.
Regards,
Jim in Santa Barbara |
Stevem123
| | Posted on Monday, November 14, 2005 - 11:30 pm: |
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Common consumer electronic devices are designed in most cases to be within +/- 10% accuracy.
Medical devices are designed within a +/- 2% accuracy or even 1% for the very critical stuff.
2 MPH error at 60 MPH is only a 3% error. I'd say that's pretty damn close.
And, no I don't worry about minimal errors like that because it aint rocket science, it's just a motorcycle. Besides that, I'm too busy with my attention on my surroundings to worry about my speed. I'm gonna get ticketed anyway if any LEO's are within radar distance!
BC Steve |
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