Fuel octane 87 or 93
03-15-2007, 08:17 PM
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RE: Fuel octane 87 or 93
I like to use "unconventional wisdom" but then again I have been known to be wrong before
I do know of at least one manufacturer that recommends against using Coleman fuel.
I do know of at least one manufacturer that recommends against using Coleman fuel.
03-16-2007, 09:07 PM
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RE: Fuel octane 87 or 93
ORIGINAL: rc bugman
Silversurfer,
3ws will run on 87 octane. If you are trying for max rpms to pull things that drag a lot, higher octane will give 300 or so more rpms. The book says 88 is minimum. I always run at least 89 to get max rpms.
In your application where engines are loafing for most of the run, the octane makes little difference.
Elson
Silversurfer,
3ws will run on 87 octane. If you are trying for max rpms to pull things that drag a lot, higher octane will give 300 or so more rpms. The book says 88 is minimum. I always run at least 89 to get max rpms.
In your application where engines are loafing for most of the run, the octane makes little difference.
Elson
Higher octane WILL NOT make more power in any normal situation (the most power you will ever make is the lowest octane at which the engine won't have ping or knock)
Highter octane WILL make an engine run HOTTER (if it is not needed) Similar to retarding the timing
Octane is a stabilizer that makes the gas burn slower
I know many of you know all of this, but for those that don't, I have barely scratched the surface about octane ratings and it might be worth your time to do a google search for octane and the different ways they rate it as there is a lot to learn about the subject.
John
03-17-2007, 01:43 AM
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RE: Fuel octane 87 or 93
Higher octane gas is also used in the cold winter air to produce higher CHT's, permitting an engine to run when it would not with a lower octane fuel. That verifys the hotter part. I know what it says in the books, but actual practice shows that several benefits are to be had in certain conditions. Hot weather and lower octane fuels, in engines designed for lower octane fuels, frequenly causes a loss of rpm. Using the higher octane fuel to delay detonation caused by hotter ambient temps helps recover some or all of the rpm that would have been sacrificed otherwise. Hence, more power.
This is from real world data obtained through many hours of very sophisticated in flight telemetry and lab testing. The carpenter books say to drive a nail you should hit it with a hammer. The book fails to tell you that if you don't want to bend the nail you should lean the nail into the swing. That part is learned from actual practice.
This is from real world data obtained through many hours of very sophisticated in flight telemetry and lab testing. The carpenter books say to drive a nail you should hit it with a hammer. The book fails to tell you that if you don't want to bend the nail you should lean the nail into the swing. That part is learned from actual practice.
03-17-2007, 09:31 AM
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RE: Fuel octane 87 or 93
I'm not going to say your testing wasn't accurate, but I've recently done some rudimentary octane tests on my own. In all honesty, I don't think it will make a bit of difference in our motors if we use 87 or 93 octane as the motor ran nearly identically with both fuels (within 20 rpm of each other at approximatly the same temp or as close as I could measure)
I also ran some 104 octane unleaded fuel in it and it was around 50 rpm less than the other 2 octanes at the same temp levels.
This testing was done with a DA 150.
When you talk about pre-detonation in hotter weather, that still goes along with the "book" and what I mentioned earlier about using the lowest octane possible without predetonation which can cause ping. If it is predetonating, then the octane isn't high enough, but if it runs on 93, without predetonation, it will not make more power on anything higher. I know there is a lot of gray area and special situations, but for most general purposes, and without trying to confuse a lot of people, this is true.
The main thing I wanted to point out by even posting to begin with was to point out why it was incorrectly stated that a 300 rpm increase (roughly 5%) would be had by buying more expensive fuel if the engine was running properly before raising the octane.
I also ran some 104 octane unleaded fuel in it and it was around 50 rpm less than the other 2 octanes at the same temp levels.
This testing was done with a DA 150.
When you talk about pre-detonation in hotter weather, that still goes along with the "book" and what I mentioned earlier about using the lowest octane possible without predetonation which can cause ping. If it is predetonating, then the octane isn't high enough, but if it runs on 93, without predetonation, it will not make more power on anything higher. I know there is a lot of gray area and special situations, but for most general purposes, and without trying to confuse a lot of people, this is true.
The main thing I wanted to point out by even posting to begin with was to point out why it was incorrectly stated that a 300 rpm increase (roughly 5%) would be had by buying more expensive fuel if the engine was running properly before raising the octane.
03-17-2007, 09:46 AM
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RE: Fuel octane 87 or 93
We're pretty much in general agreement. In my original posts, and maintained throughout, it was noted that gains would be minor. The largest benefit is during the hottest weather periods since usually few are out flying when air temps are at 32f and under. Never tried gas blends over 100 octane, so that's interesting about the 104. Either of those are difficult to locate for most people and quite expensive.
03-17-2007, 10:33 AM
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RE: Fuel octane 87 or 93
ORIGINAL: rc bugman
Silversurfer,
3ws will run on 87 octane. If you are trying for max rpms to pull things that drag a lot, higher octane will give 300 or so more rpms. The book says 88 is minimum. I always run at least 89 to get max rpms.
In your application where engines are loafing for most of the run, the octane makes little difference.
Elson
Silversurfer,
3ws will run on 87 octane. If you are trying for max rpms to pull things that drag a lot, higher octane will give 300 or so more rpms. The book says 88 is minimum. I always run at least 89 to get max rpms.
In your application where engines are loafing for most of the run, the octane makes little difference.
Elson
--------------
I run 89 to avoid some of the additives that the EPA insists the oil companies put in their most sold/popular fuel. Many times the higher octane fuels aren't saddled with the oxidizers and such, or so I've heard. Were it not for the additives, I'd run 87 myself. But, I do not own any engines (now) that higher octane is called out for in the engine manual. I'd have to think twice about running lower octane fuel if the manufacturer/distributor specifically said to do so.
My motorcycle manual (vee twin four-stroke) claims 93 octane is needed, while all of the engine rebuilders I have talked to say that running 87 carbons up the rear cylinder in my style of vee-twin. Who do you believe? The manufacturer, or the guys that rebuild them?
I wonder what effect various oils have (used in model gas engines) on the aggregate octane rating of the gasoline? If any.
Ed Cregger
03-17-2007, 10:40 AM
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RE: Fuel octane 87 or 93
ORIGINAL: Silversurfer
We're pretty much in general agreement. In my original posts, and maintained throughout, it was noted that gains would be minor. The largest benefit is during the hottest weather periods since usually few are out flying when air temps are at 32f and under. Never tried gas blends over 100 octane, so that's interesting about the 104. Either of those are difficult to locate for most people and quite expensive.
We're pretty much in general agreement. In my original posts, and maintained throughout, it was noted that gains would be minor. The largest benefit is during the hottest weather periods since usually few are out flying when air temps are at 32f and under. Never tried gas blends over 100 octane, so that's interesting about the 104. Either of those are difficult to locate for most people and quite expensive.
I agree and I know you know what you're talking about, I just didn't want to try and make people reading this trying to learn more confused than necessary.
And yes the 104 was very expensive at $7.15 a gallon.
It wasn't you, but someone did mention a 300 rpm increase from higher octane, and that was the main point I wanted to point out as being wrong and not to let people get misled.
03-17-2007, 06:34 PM
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RE: Fuel octane 87 or 93
3W engines are actually supposed to run higher octane gas, so the big jump in rpm for those engines is not out of line at all had they been running lower octane fuels. There could have been a misunderstanding there. For engines with average compression see that kind of bump by going to high octane... ain't gonna happen.
Those that are desparate for just another 50-100 rpm out of their engines to do what they want to do would be far better off getting a larger engine and not working it as hard to obtain more power than they had before. One thing I have a problem with and that's being on the edge with the amount of available power versus what I need to have for the performance I want. Too much juggling, while it's easier, safer, and more productive just to go bigger. There's the arguements that larger engines are heavier, but too much concern over a few grams or ounces indicates there may be another set of problems. If there's that much concern about the weight, then the power level may be even more marginal than fuel or props could ever hope to overcome.
Those that are desparate for just another 50-100 rpm out of their engines to do what they want to do would be far better off getting a larger engine and not working it as hard to obtain more power than they had before. One thing I have a problem with and that's being on the edge with the amount of available power versus what I need to have for the performance I want. Too much juggling, while it's easier, safer, and more productive just to go bigger. There's the arguements that larger engines are heavier, but too much concern over a few grams or ounces indicates there may be another set of problems. If there's that much concern about the weight, then the power level may be even more marginal than fuel or props could ever hope to overcome.
