MPG?

[helicopterjim R.I.P.]

I may have mentioned this before but I get my best and worst gas mileage after installing 11:1 pistons, AND way more fun.

[johamilt]

I think I'm getting the lower-end figures for my 2002 scura (stock): about 25 mpg in-town and 40 mpg on the highway @ 3000 miles on odometer. However, I'm a grad student and ride to school daily in extremely stop-and-goish traffic, keeping rpms around 2-3,000 most of the time

 

My question for this forum, though, is how much the octane figure affects the engine/mpg. I use 90+ octane, but with prices soaring, the lower octanes look tempting (did I mention being a grad student?). I haven't seen but one reference (someone said they used 89 octane) to octane figures. Does lower octane create greater engine wear?

 

chau!

[Lex]

I think I'm getting the lower-end figures for my 2002 scura (stock): about 25 mpg in-town and 40 mpg on the highway @ 3000 miles on odometer.  However, I'm a grad student and ride to school daily in extremely stop-and-goish traffic, keeping rpms around 2-3,000 most of the time 

 

My question for this forum, though, is how much the octane figure affects the engine/mpg.  I use 90+ octane, but with prices soaring, the lower octanes look tempting (did I mention being a grad student?).  I haven't seen but one reference (someone said they used 89 octane) to octane figures.  Does lower octane create greater engine wear?

 

chau! 

35072[/snapback]

 

Octane has no effect on mileage (or power) unless the engine management systems uses knock sensors to run as much advance as the fuel will tolerate. The Guzzi doesn't have this kind of system so your mileage will not be effected. Engine wear is in no way connected to octane rating. That you think either of these might be true shows you what a great job the oil companies have done lying to the public about fuel.

 

What lower octane can do is allow the fuel to either burn before the spark (pre-ignition) or spontaneously explode while the mixture is burning. Both of these will produce a sharp sound like somebody hitting your bike's head with a hammer. It sounds like that because that is basically what is happening. Instead of smooth burning and expansion the force of the abnormal combustion is like a hammer blow in the cylinder, strong enough to crack a piston or head. This is especially nasty since the pinging (American slang, I think the Brits call it pinking) also exposed your cylinder, piston and head to more heat. Since heat is part of the problem the next time around pinging is more likely. Finally, aluminum gets weaker quickly as temperatures rise. This a vicious cycle that can destroy an engine. Priced a set of pistons and heads lately?

 

How much octane do you need? Enough to stop abnormal combustion. On the type of short rides you are talking about (very short) you could probably run 87 octane without problems since one of the major factors is heat. On a short ride your engine doesn't have time to get hot. You can also add air temperature, the cooler it is the less octane you need to avoid problems. Other factors are time, the slower the engine is turning the longer the fuel has to explode, and throttle, the bigger the throttle opening the more mixture you get into the cylinder making the pressure higher spontaneous combustion more likely.

 

Airhead BMWs have a truly poor combustion chamber. Even with an 8.7 to 1 compression ratio on 91 octane fuel they ping at certain throttle position/ RPM combination on a hot day. The solution is to cool the combustion chamber by adding fuel (normally changing the needle jet from a #266 to a #268) since this is illegal here in the Golden State people often deal with this by not riding in the RPM range (around 3500 RPM) where this happens. An interesting side note is that adding a second spark plug lets the needle jet be reduced to a #264, even leaner than stock, and banish the pinging. Why? Because the timing is retarded since it takes less time to burn the fuel when the burn starts in two places. I've seen the combination of dual plugs and bit more compression, jetted properly and with the timing adjusted, add a nice power increase and a 30% improvement in mileage. Hum... My GS had a 9 gallon tank, at 35 MPG I could go a bit over 300 miles on a tank, with a few modifications I could have done a 1000 mile day on only 2.5 tanks...

 

The bottom line is how risk adverse you are. You can take a chance and run lower octane fuel. If you engine runs well you will save a few bucks, if you let it ping your potential down side is huge. Feeling lucky?

 

Lex

[johamilt]

How much octane do you need? Enough to stop abnormal combustion. On the type of short rides you are talking about (very short) you could probably run 87 octane without problems since one of the major factors is heat.

 

The bottom line is how risk adverse you are. You can take a chance and run lower octane fuel. If you engine runs well you will save a few bucks, if you let it ping your potential down side is huge. Feeling lucky?

 

Lex

35082[/snapback]

 

Thanks very much, Lex, for such a complete and detailed response! I have a much better idea of what to listen/look out for when choosing my gas. Since winter riding here in Indiana is fast approaching, I think I will try a lower octane--with caution, since my risk adversity lies somewhere between the delicious, sharp corners of a country road and an instructor's bread-crumb stipend.

 

jh

[robbiekb]

I'm getting about 120 miles before the low fuel light flickers to life, mostly sitting around the 4500 - 7500 rpm levels in my backroads commute.

[Guest rosso mandello]

My mileage is getting worse, last time i got constant light on was around 170 km, that is about 10 km/liter, remind you that the gasoline in Denmark is 10 kroner/liter I am almost ruined. I spend a lot of my ridning time around 5000 to 6000 rpm.

 

I have ordered time at my repair shop, hoping he can tweek the PCIII to get my mileage up.

 

My 4000 km trip to Italy in june is not in danger, but could be more fun at 16 - 18 km/liter.

 

My plugs are black, not brown or grey, so I hope the tweeking helps

 

In Denmark summer is up, up to 20 degrees in the next 5 days, no rain.

 

Life is good

 

Mogens.

[Alex-Corsa]

 

My plugs are black, not brown or grey, so I hope the tweeking helps

 

Life is good

 

Mogens.

 

Seems like your bike is running rich miture of fuel.Well, before doing anything on the mixture , be sure about your injection system being adjusted and working correctly.i.e. synchronisation , TPS voltage at least, they

play significant role to the consumption. In my experience these can effect on fuel consumption 0-10%(of course in same setup,before-after situation)

I have an approximate 6-6.5lt/100km on autobahn speed travel (120-160km/h) and about same on country sport (not extreme) riding, and a 6.9-8 in city

even though I have programmed my chip on the injection to get a 12.2 -12.9AFR at the exhaust.

[Skeeve]

Seems like your bike is running rich miture of fuel.Well, before doing anything on the mixture , be sure about your injection system being adjusted and working correctly.i.e. synchronisation , TPS voltage at least, they

play significant role to the consumption. In my experience these can effect on fuel consumption 0-10%(of course in same setup,before-after situation)

 

Black spark plugs? All of the above, & let's not forget the obvious: what's your air filter look like/when was it last changed or cleaned? Definitely running way too rich w/ black plugs; something is amiss!

What about spark? Got a known good ECU that could be swapped in quickly? You mention a PCIII; unplug it, & see if that's the source of trouble; no way your plugs should be that dark if the bike is running properly. No wonder your mileage is shot!

 

[Guest Nigelstephens]

I always thought my Sport I gas mileage was poor but reading this thread I feel more happy.

On Sunday last I acheived 44mpg (imp) on a tank. This was mostly crusing at 60-70mph. That is about 180 kms on the clock before the light comes on. Sorry about the mix of units but the speedo is in kms and I tend to think in mpg for consumption figures.

 

Have recently advanced ignition by about 2 degrees from the std my16m map at crusing speeds and seen an improvement of about 2mpg! AFR is set for 13.1 when crusing and 12.5 for power.

 

My plugs can appear sooty sometimes but this is when I have been going slow before parking in my garage. If I stop quickly and kill the engine from a crusing speed the plugs look spot on.

[Guest rosso mandello]

i run an K&N filter, new from last year. For storeage this winter i cleaned it with the original cleaner supplied from K&N, is there a chance I got too much oil on it by mistake.

 

For the other tecnical stuff i go to my dealer soon, he has a computer and a dyno so I hope......

 

 

mogens

[Skeeve]

Have recently advanced ignition by about 2 degrees from the std my16m map at crusing speeds and seen an improvement of about 2mpg! AFR is set for 13.1 when crusing and 12.5 for power.

 

With EFI, you should be able to run at least 13.5:1, if not 14:1, in a cruise. Stoichiometric is 14.7:1 (ie, d@mn close to 15:1) Try a colder plug if need be, but you should be able to get better mileage when cruising & save the over rich conditions only for when running in "power" mode, I should think...

 

[Guest NotRight]

i run an K&N filter, new from last year. For storeage this winter i cleaned it with the original cleaner supplied from K&N, is there a chance I got too much oil on it by mistake.

 

For the other tecnical stuff i go to my dealer soon, he has a computer and a dyno so I hope......

mogens

You are now in Denmark? Very cool concept....... Lovely area too. Suppose I have nothing to say about your question though.

[Guest Nigelstephens]

With EFI, you should be able to run at least 13.5:1, if not 14:1, in a cruise. Stoichiometric is 14.7:1 (ie, d@mn close to 15:1) Try a colder plug if need be, but you should be able to get better mileage when cruising & save the over rich conditions only for when running in "power" mode, I should think...

 

 

I have tried an AFR of 14 -13.5 but I did not gain any improvement in consumption, only hesitancy.

[luhbo]

I have tried an AFR of 14 -13.5 but I did not gain any improvement in consumption, only hesitancy.

 

Yes, I think I experienced the same. The hesitancy is compensated by a wider throttle opening. There is no gain without some mental training, means you just should accept the weak feeling.

 

Can you accept the hesitancy when you want to correct your corner radius?

 

It may be the same effect that gives a better mileage with dual pluged heads. The engine responses quicker, so you can leave the throttle more closed for the same acceleration.

 

Hubert

[Alex-Corsa]

Octane has no effect on mileage (or power)

 

Dunno how exact , but I start believing that it does, after my yesterday's experience to "feed" my bike with lower octan (still OK for the bike) of 95 unleaded, had a 8-10% more lean indications in my AFR instrument,(where I was having 12.8 was getting 13.9-14++) and the bike wouldn't go as good as before with the 98 or 100 octane I used to do my tunning an measurments. For a moment I though WTF but then I remembered

I went that ride and burned that fuel ,and on the return just filled up , with 100, bingo! the bike came back up as alive and good functioning as before.

Dunno what all that translates to power and or miliage but for sure there must be something hiding there.

 

I have tried an AFR of 14 -13.5 but I did not gain any improvement in consumption, only hesitancy.

 

This AFR on and steady when cruising , or when accelerating? you see there are different throtle openings for that. A throtle opening on the 5th speed on the 1100i when cruising (about straight)at 4000rpm is at around 18-20deg. when accelerating is a bit wider and then depending on the gear and or load..