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OK, the M695 is my first bike and soon it's going to need gas.

Question #1: Here in CA 91 octane is as good as it gets. The manual calls for 95, but that must be one of the alternative calculation methods, right? Any reason not to use 91?

Question #2: I've never gassed up a bike before. :-[ Is the proper technique to hold back the vapor thingy and visually check the level as it fills? Short of fuel spilling all over, will it be obvious when I'm topped up and not overly full?

BK
 

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Welcome and congrats on your monster! You should come join the gang at Zeitgeist in SF on the last Thurs of each month. [thumbsup] We'll be there on the 30th. Check the Bay Area local board (MOB -- look below) for more info as the date gets closer.

1) You've stumbled onto a much debated question (see the ultimate gas thread). The reason not to use 91? It costs more and some say it can cause carbon build up. The 95 does not refer to US standards of gas. I *think* it converts to somewhere between 89 and 91. Most people will tell you to use 87 unless you hear a pinging. Some will only use 91 on their babies. I use 87, but that's not because I know anything special. It works just fine, so that's what I do.

2) Yup, you've got it right. Just pull back the black gas pump foreskin and hold it back while you fill. Don't fill it up at full blast or it might splash everywhere. Go like 3/4 strength. And don't stick the pump as far in as it will go, like you would with a car. Put it in at an angle, and only a few inches. [Jeez, sounds like I'm talkin' about something else here, don't it? >:D ]

It will be obvious when it's nearly full. You will hear it start to fill up and see gas well before it tops off. Don't try to squeeze every last bit in there. Inevitably, you'll overfill and get gas on your tank. Not a big deal if it happens.
 

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BK_856er said:
OK, the M695 is my first bike and soon it's going to need gas.

Question #1: Here in CA 91 octane is as good as it gets. The manual calls for 95, but that must be one of the alternative calculation methods, right? Any reason not to use 91?

Question #2: I've never gassed up a bike before. :-[ Is the proper technique to hold back the vapor thingy and visually check the level as it fills? Short of fuel spilling all over, will it be obvious when I'm topped up and not overly full?

BK
Sorry, I have the title of Ultimate Noob here. Why? Cuz I asked the same fueling question few weeks ago :p But what Spidey said.

My retarded refueling thread: http://www.ducatimonster.org/smf/index.php?topic=64160.msg798199;topicseen#msg798199

As for Octane, I use 87 on my '01 750. After 800+ miles of daily driving with all 3 types for approximately 1 week each, I see no difference in performance except in gas mileage. Here are the results for me:


Driving Style: Few miles of surface street and rest cruising at about 6-7k rpm on freeway.
91 Octane: Approx 3.1-3.3 gallons. Light up at 90-100 miles.
87 and 89 Octane: Approx 3.1-3.3 gallons. Lights up at about 135+ miles.

Logical choice was to save and use 87 for me.
 

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Vicynax said:
Sorry, I have the title of Ultimate Noob here. Why? Cuz I asked the same fueling question few weeks ago :p But what Spidey said.

My retarded refueling thread: http://www.ducatimonster.org/smf/index.php?topic=64160.msg798199;topicseen#msg798199

As for Octane, I use 87 on my '01 750. After 800+ miles of daily driving with all 3 types for approximately 1 week each, I see no difference in performance except in gas mileage. Here are the results for me:


Driving Style: Few miles of surface street and rest cruising at about 6-7k rpm on freeway.
91 Octane: Approx 3.1-3.3 gallons. Light up at 90-100 miles.
87 and 89 Octane: Approx 3.1-3.3 gallons. Lights up at about 135+ miles.

Logical choice was to save and use 87 for me.
Something here doesn't add up...changing gas will not give a bike a 40% increase in fuel efficiency
 

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OT said:
Something here doesn't add up...changing gas will not give a bike a 40% increase in fuel efficiency
I got about 30%, but why not?
 

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Here's how I understand it:

* The energy content of gasolines (BTU/gal) is fairly uniform, so engine will combust the gas in similar manner (and same mileage)
* Octane number in gasoline is a measure of antiknock properties, not energy content, to address range of engine compression ratios encountered in motor vehicles
* Additives, such as ethanol, might change the energy content but would have to be added in significant amounts (>5%) to see a difference. Ethanol would tend to lower the energy content.
* Unless the lower octane fuel burned much hotter, which would improve combustion efficiency, the mileage won't change. Major way to make an engine run hotter is to increase compression ratio.
* Based on the gas you both say you're using, the bikes run smoothly on all octanes from, say 89, up. So the compression ratio isn't a factor here.

So, there's gotta be something else going on here than just a change in octane rating of the gas you're using
 

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OT said:
Here's how I understand it:

* The energy content of gasolines (BTU/gal) is fairly uniform, so engine will combust the gas in similar manner (and same mileage)
* Octane number in gasoline is a measure of antiknock properties, not energy content, to address range of engine compression ratios encountered in motor vehicles
* Additives, such as ethanol, might change the energy content but would have to be added in significant amounts (>5%) to see a difference. Ethanol would tend to lower the energy content.
* Unless the lower octane fuel burned much hotter, which would improve combustion efficiency, the mileage won't change. Major way to make an engine run hotter is to increase compression ratio.
* Based on the gas you both say you're using, the bikes run smoothly on all octanes from, say 89, up. So the compression ratio isn't a factor here.

So, there's gotta be something else going on here than just a change in octane rating of the gas you're using
I believe ethanol/methanol blends are in the 10% range. http://tinyurl.com/g4qb9
The lower octane, as I understand it, burns faster. If the higher octane wasn't burning completely there would be a bunch of wasted fuel.

My experience is they run smoother on 89 down with stock compression ratios.
 

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OT said:
Something here doesn't add up...changing gas will not give a bike a 40% increase in fuel efficiency
It doesn't. But somehow it just happens on my bike. I would think 1 week of daily riding about 80 miles daily is enough to justify 91 octane a waste on my bike. I wanted to test out the different octanes since after reading that whole 50 page octane thread, all answers were still pretty vague. Doesn't add up, but I'm happy I run great on 87 ;D
 

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Discussion Starter · #10 ·
Wow! Thanks for the info, guys. My head is still spinning from that mega-thread on gas and octane. I did a double-take when I saw Jim Conforti chime in. When Jim talks, I listen. The man is a legend in tuning BMW Motronic code, and I had no idea was into Ducatis for fun. With 10.5 compression and an air-cooled engine I think I'm going to start out conservatively and go with 91 gas.

Thanks again for the warm welcome and advice - you guys rock!

BK
 

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The difference in fuel economy would come from slight missfire on the 91. The missfire also causes carbon build-up. This is due to the reformulated gasoline used in most of the country. The missfire is not from the higher octane, but from the additive package. The problem seems to be the stuff doesn't want to atomize. I have heard of as much as a 5 HP loss on superbikes on the dyno from reliable sources. If Jim talks about BMWs I will listen, but by his own admission he has never monitored a Duc on a dyno. I might be concerned with the deep sump engines since they are new, but the other ones have been around for years without signs of detonation when cylinder heads came off.
 
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