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General Category => General Discussion => Topic started by: handyandy on May 04, 2016, 03:11:47 PM
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OK Mary and I are planning to go to John Day in June. We live in central Indiana. Elevation about 500 ft. I have heard that 92 octane at high altitude is a waste of money. What is the story?
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500? Maybe 5000 ft. I noticed out west in the higher altitudes they sell lower octane. If you use premium here you'll find premium along the way but at altitude the number will be lower.
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Andy, I live at 4000ft elevation and regularly take the 20 minute ride to Bisbee which is 5000-5200 ft I have to run high octane premium in my Lemans, and Eldorado, or they will ping. On my hydro, I can run any gas, no pinging, no difference. I am not sure if its the gas, the altitude,or the more advanced engine controls on the 2003hydro,
Rick.
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My hydro is as good at sea level as at
(http://thumb.ibb.co/kGBJdv/berthoud_pass.jpg) (http://ibb.co/kGBJdv)
It simply does not care about altitude. It also runs on whatever I feed it. I have occasional disagreements about the suitability of gas at a particular fillup, but overall, if I can pump it I can run it.
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Mine gets high on whatever gas I put into it.
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The higher the altitude the thinner the air = you need less octane. So at higher alt. you get the highest octane they sell, which might be 87. 5K' isn't that high in the overall picture. It's when you get to 7K' or higher that you feel power loss in your bike unless you have CV carbs or closed loop EFI.
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My Bassa never had a problem in the Rockies and mileage was increased to well into the 50mpg range.
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I always use the cheap stuff. It is generally a waste to use anything better.
But more than once I have traveled to the coast in Florida, gotten detonation on my 2004 EV, and had to bump up the octane. At 1000 feet and higher here in Georgia, it isn't an issue.
I have also had that EV to Wyoming, Montana and Colorado, towing a camper, and used the 85 octane stuff they have, with zero issues.
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I suppose the argument goes, for a normally aspirated engine, if you go high enough, it will effectively lower the compression in the engine as the air is thinner. With lowered compression, theoretically, it might be able to run on lower octane. (This argument probably sounds better after a few beers.)
In practice, it would be hard to keep the right fuel in the tank if you're travelling.
I haven't heard of any stations systematically offering lower octane in their fuels at higher altitudes. This is a good thing as there are plenty of turbocharged engines that would maintain the same compression in the engine regardless of the altitude.
Just keep using the same grade of fuel you're used to.
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Cool, an octane thread.
An "oil thread" for the less lubricious among us... Yeah, I know.
Todd.
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I haven't heard of any stations systematically offering lower octane in their fuels at higher altitudes. This is a good thing as there are plenty of turbocharged engines that would maintain the same compression in the engine regardless of the altitude.
Just keep using the same grade of fuel you're used to.
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Then obviously you have never ridden to areas of higher altitude where 86 or 85 may be the highest octane offered. :wink: I have.
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I live at 6700ft. My local gas station is just a bit over 7000ft. High octane is 92. Don't remember any gas stations I've stopped at in NM, UT, AZ or CO where they did not have >90 octane. Maybe just the places I picked to stop at.
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I haven't heard of any stations systematically offering lower octane in their fuels at higher altitudes. This is a good thing as there are plenty of turbocharged engines that would maintain the same compression in the engine regardless of the altitude.
I had never seen or heard of 85 octane until I got to the Rockies. There, 85 octane was common from stations that carried 87 octane elsewhere.
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Yep. In The Rockies, stations will usually have several options: 85, 87, 89,90. Sometimes 91 or 92.
A few of the old dumpy stations may only offer 85 and 87.
I try to use 88 or higher, at high altitudes. My bikes usually go up into the 50s on mpg.
Down here in The Ozarks at 500-2500 feet, I run 91 or 93.
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I haven't heard of any stations systematically offering lower octane in their fuels at higher altitudes. This is a good thing as there are plenty of turbocharged engines that would maintain the same compression in the engine regardless of the altitude.
85 is the "standard" all up and down The Rockies... I had never seen that until my first trip there..
Shell, Conoco, Exxon... They all "systematically" supply lower octane fuels at mile-high-plus altitudes in The Rockies..
(http://theautorules.com/wp-content/uploads/2014/07/HPIM2444.jpg)
(http://farm4.static.flickr.com/3050/2626886947_5ef83ddd0c.jpg?v=0)
(http://www.durangoherald.com/storyimage/DU/20151019/NEWS01/151019725/AR/0/AR-151019725.jpg&ExactW=620)
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I suggest some of you guys go to places like Glacier National Park and see what your octane options are. Maybe if you stay on high volume roads like freeways you have more choices, but when you get on a 2 lane road/hiway, your choices are few. Your bike still runs OK.
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I suggest some of you guys go to places like Glacier National Park and see what your octane options are. Maybe if you stay on high volume roads like freeways you have more choices, but when you get on a 2 lane road/hiway, your choices are few. Your bike still runs OK.
I only ride interstates. If I can't see it from the interstate, it doesn't exist...
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Here in mountainous RI, the highest point is Jeremoth Hill, alt. 812 ft. No gas stations there, but the closest one is a run-down one-grade operation that sells only "regular", 87 octane, same as on the coast ;-).
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There WILL be gas stops that only offer 86 octane.
No big deal. Even at higher elevations, I usually use the highest octane available whether it is necessary or not. The extra $0.9 makes no difference to me.
Good on you, Andy, for coming to John Day. You are going to have a great trip!
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Mary will be on a Cal II I will be in a 93 Cal III. My experience last time out west was to be thankful for any gas at all. If you see gas at 100 miles, pull in and fill up.
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No problems using the same grade on fuel injection bikes regardless of the octane number. I use 87 in the Goldwing at 300 feet and get around 45 mpg. Out around 4 corners I was puting in 85 octane and getting 55 mpg. Not a quirk as it was 55 mpg over at least 5 tankfulls. Mileage dropped back down to 45 as I headed back east. On my carbed bikes, the BMW with diaphragm carbs seem to compensate for altitude. The Norton with slide carbs did not and would have required a jetting change if I wasn't just passing through.
Pete
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For those who say a CV carbed bike suffers none at altitude, you will be surprised when it happens. Or disappointed. Or both.
BTDT.
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As higher the field elevation, as lower the air density. A carburator engine has only one setting, the lack of air at high field elevations results in a richer (up to way too rich) air/gas mixture which causes the well known lack of power. Engines with EFI can compensate this by injecting less fuel at higher altitudes, the loss of power is there as well, but not so significant and the drivability remains OK. Octane numbers have no influence on that. Small Cessnas f.e. fly with Avgas 100LL, and planes have nothing else to do than to climb to altitude. The pilot in a piston engine Cessna monitors the exhaust temperature
and has a control knob to lean the mixture more and more as higher he gets - "manual" fuel supply, no octane issues:-)
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For those who say a CV carbed bike suffers none at altitude, you will be surprised when it happens. Or disappointed. Or both.
BTDT.
I rode my Suzuki VX800 2up across Colorado over Vail(10,666') & Loveland(11,990') passes w/CV carbs and no other vehicle could keep our pace including a MB diesel. PeteS made reference to his BMW w/CV carbs(diaphragm). I'm not saying we didn't lose any power but we had more power than anyone else there and power to spare.
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Not because of thinner air its actually lower pressure(atmospheric, less BMEP!). Along I-40 thru NM the places I stop at are 90 tops.
:-)
You must not stop in Albuquerque, Grants or Gallup. Alb is mostly 91 and 92. This morning when I fueled up at a Chevron station on I40 in Alb I got 92.
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As higher the field elevation, as lower the air density. A carburator engine has only one setting, the lack of air at high field elevations results in a richer (up to way too rich) air/gas mixture which causes the well known lack of power.
This demands a little explication. An airplane carburetor has a continuous mixture control. In addition to a tachometer, you have a manifold pressure gauge and cylinder head temp and exhaust gas temp gauges. So you have a pretty clear idea of what's going on in the combustion chamber. The engine's octane requirement is specified for max power at sea level. It wouldn't make sense to fuel with a lower octane at a high-elevation field because some of that low-octane fuel may still be in the tanks when you arrive at a sea-level airport.
Before takeoff, you adjust mixture for best power, and lift off at full throttle (and at highest rpm if you have a constant-speed prop). During cruise-climb you can back off the rpm but usually maintain full throttle. At cruise altitude you level off, reduce rpm and throttle to cruise settings, stabilize airspeed and altitude, then lean out the mixture to peak exhaust gas temp and little beyond -- that is, to about 20F lean of peak. That's the most economical cruise, it gives the cleanest burn (less carbon and lead deposit on plugs, valves and piston) and a cooler cylinder head temp than running a bit rich rather than a bit lean. This all supposes that the cylinders are equidistant from the carb so all cylinders get the same fuel/air mix -- that's more likely to be true of four-cylinder engines than sixes. Six-cylinder engines may be better off with well-balanced fuel injection. Potential mixture imbalance is why it's better to have EGT/CHT readings on each individual cylinder. Adjust for safe running on the hottest cylinder (and this is a good reason not to use one carb on a four-cylinder motorcycle).
On descent to landing, you return all engine controls (except throttle) to take-off power positions, in anticipation of a go-around.
That's for a normally aspirated engine. A turbocharged engine may have different requirements based on boost pressure.