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Old 07-04-2011, 11:42 PM   #76
110Mike
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Hilarious!

"Fuel economy". And "Airhead" are words that should not be in the same sentence.....

Seriously though my R100RS gets 31 -32 mpg but can be better. I have seen 35 - 36 mpg before the previous carb adjustment. I usually goes better than 90 mph

My R80ST returns about 35 mpg. Also mostly at 90 mph.
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Old 07-04-2011, 11:53 PM   #77
supershaft
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Wait a minute. I reported usually getting high twenties and that is not even on the chart. 29-31 is not high twenties. Put a slot on there for me. 26-29.
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Old 07-05-2011, 05:38 AM   #78
Big John Sny
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Quote:
Originally Posted by Wirespokes View Post
I'll bet those of us with higher compression engines get the better mileage.

Vehicles in Brazil and elsewhere in S Amarica burn alcohol, not gasoline. The Vincent Black Shadow (or was it the Lightning?) was set up for alcohol and had a 5mph higher top end.

So it's not true that alcohol won't work as a fuel. But what is important is that engines running on alcohol require higher compression - like 14:1 - to extract the energy from it.

Not even considering the alcohol, higher compression ratios are more efficient and return more miles per gallon, besides having more horsepower.
A properly set up alcohol engine can perform very well. Alcohol has a naturally higher octane rating.

"As a fuel, methanol and ethanol both have advantages and disadvantages over fuels such as petrol (gasoline) and diesel fuel. In spark ignition engines, both alcohols can run at a much higher exhaust gas recirculation rates and with higher compression ratios. Both alcohols have a high octane rating, with ethanol at 109 RON (Research Octane Number), 90 MON (Motor Octane Number), (which equates to 99.5 AKI) and methanol at 109 RON, 89 MON (which equates to 99 AKI).[2] Note that AKI refers to 'Anti-Knock Index' which averages the RON and MON ratings (RON+MON)/2, and is used on U.S. gas station pumps. Ordinary European petrol is typically 95 RON, 85 MON, equal to 90 AKI. "

BUT alcohol still has less energy per volume. This means in an engine that does not run higher compression ratios, to take advantage of the higher octane, the engine will produce less power per volume of fuel and get worse fuel milage. In a higher compression engine the higher compression advantage and lower energy density balance each other out and it is a wash. The alcohol will produce less emissions either way.
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Old 07-05-2011, 11:33 AM   #79
BrokenR80RT OP
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Laugh

Quote:
Originally Posted by supershaft View Post
Wait a minute. I reported usually getting high twenties and that is not even on the chart. 29-31 is not high twenties. Put a slot on there for me. 26-29.
Supershaft!

Sorry....but it was difficult to decifer your information Vs. ranting about the question...Next time, buddy.

BRT
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Old 07-05-2011, 12:05 PM   #80
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Thumb John...

Quote:
Originally Posted by Big John Sny View Post
A properly set up alcohol engine can perform very well. Alcohol has a naturally higher octane rating.

"As a fuel, methanol and ethanol both have advantages and disadvantages over fuels such as petrol (gasoline) and diesel fuel. In spark ignition engines, both alcohols can run at a much higher exhaust gas recirculation rates and with higher compression ratios. Both alcohols have a high octane rating, with ethanol at 109 RON (Research Octane Number), 90 MON (Motor Octane Number), (which equates to 99.5 AKI) and methanol at 109 RON, 89 MON (which equates to 99 AKI).[2] Note that AKI refers to 'Anti-Knock Index' which averages the RON and MON ratings (RON+MON)/2, and is used on U.S. gas station pumps. Ordinary European petrol is typically 95 RON, 85 MON, equal to 90 AKI. "

BUT alcohol still has less energy per volume. This means in an engine that does not run higher compression ratios, to take advantage of the higher octane, the engine will produce less power per volume of fuel and get worse fuel milage. In a higher compression engine the higher compression advantage and lower energy density balance each other out and it is a wash. The alcohol will produce less emissions either way.
Big Johnny,

I'm with you. I think in the case of airheads, you'd need to increase the compression ratio so much to take advantage of the ethanol, you'd never get to use gasoline again. Ethanol by volume has about 32% less BTU output than the same volume of gasoline, leaving the CR and possibly a turbo the only way to become as efficient with the ethanol.

Maybe a variable CR engine would do the trick so one could run on gasoline, ethanol or blends. Typically with a single compression ratio set up for gasoline (around 9.5/10.5:1), these E-85 cars you see running around lose about 25% fuel economy with ethanol. They only lose 25% because the blend is still 15% gasoline + the spark timing gets adjusted to optimize performance with the blend.

Ideally for efficiency, one would go with a turbo diesel. I am surprised noone has used the higher deisel compression ratio and turbo to convert one to ethanol, but I doubt the diesel fuel system could handle alcohol. CNG is now showing up on diesels with a simple conversion, maybe ethanol is next?

I've thought about ways to convert an airhead to a turbo diesel, but without some professional help (maybe psychiatric) I'd end up with an inefficient mess. It'd definitely require some torque limitting or the tranny, main bearings, and possibly heads would be shot and I'd be laying somewhere behind my bike, all broken again . The engine would also need to be isolated to keep the frame from imploding under the stronger diesel vibration.

Doesn't look like we are quite there yet.

BRT
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Old 07-05-2011, 03:36 PM   #81
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Just did 8,400 miles earlier this summer. Got between 40mpg (nasty headwinds) and 53mpg on a 72 R75/5 SWB. I averaged around 47mpg though. Cruising speeds consistently averaged 70-75 MPH (except for headwinds) with no fairing. Bike was loaded with a 170 lb rider and about another 70lbs of gear.
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Old 07-05-2011, 04:03 PM   #82
supershaft
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Originally Posted by BrokenR80RT View Post
Supershaft!

Sorry....but it was difficult to decifer your information Vs. ranting about the question...Next time, buddy.

BRT
I bet that's right! Ranting on and on was kind of my point regarding the complexity of a good answer to that simple question. I still think many are describing their best mileage as their average mileage.
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Old 07-05-2011, 04:31 PM   #83
DandyDoug
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Yo, Odinie:

Sounds like the trip of a lifetime, any chance for more detail and some pictures ???
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Old 07-05-2011, 05:14 PM   #84
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46MPG... just like it says in the Owners Manual
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Old 07-05-2011, 06:39 PM   #85
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My '76 R90/6 got around 40 on average.
My '83 R80RT (with fairing removed) gets around 35-37.
Both with easy riding, not loaded or high speed.

The worst mileage by far out of my bikes. Even my 1800cc Stratoliner got above 45. But the airheads sure sound good.
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Old 07-05-2011, 06:58 PM   #86
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Quote:
Originally Posted by bmwhacker View Post
Fuel economy?....... ..... 25 on a good day. The big tank still ain't big enough.

Looks pretty cool doing it, though.

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Old 07-05-2011, 07:34 PM   #87
supershaft
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Why hasn't anyone converted a diesel to alcohol? Mileage. You can't make up for 30% less energy with compression, you have to make it up with volume. There's not enough room to carry that much juice.
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Old 07-05-2011, 07:42 PM   #88
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Originally Posted by DandyDoug View Post
Yo, Odinie:

Sounds like the trip of a lifetime, any chance for more detail and some pictures ???
Yep! I'm scanning film from the trip, and will be starting my ride report next week! Will keep you posted!

_O
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Old 07-05-2011, 08:19 PM   #89
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Originally Posted by Odinie View Post
Just did 8,400 miles earlier this summer.
Earlier this summer? Technically, summer began about 15 days ago and here in Seattle we just had our first 80 degree day in over 300 days this past weekend.

I gotta get outta here because it seems that elsewhere summer begins much earlier. Good to hear that some folks are enjoying it.
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Old 07-06-2011, 07:30 AM   #90
durtwurm
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My '78 RS with the big Bings , tuned and running well never does better than about 35 mpg.

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