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/cgi-bin/YaBB.pl General Category >> Rubber Side Down! >> Octane Question. /cgi-bin/YaBB.pl?num=1372605611 Message started by gerald.hughes on 06/30/13 at 08:20:11 |
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Title: Octane Question. Post by gerald.hughes on 06/30/13 at 08:20:11 I was taught that the only reason for octane in gas was to retard ignition, specifically pre-ignition in a cylinder. I was also taught that if the compression ratio was 10:1 or lower in the cylinder, then gas with an octane rating of 87 would be sufficient. Lately, I have been looking at bikes with compression ratios below 10:1 where the manufacturer is recommending 91 octane for the engines. Can anyone explain the reason behind this to me? Thanks |
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Title: Re: Octane Question. Post by Serowbot on 06/30/13 at 09:34:51 I suppose some might recommend it at 9.5 compression...,10:1 is not set in stone... ... but,... most performance vehicles today will be fuel injected, and will have an automatic timing retard if the CPU senses engine knock... so the vehicle won't suffer any damage with regular... it might take a slight performance hit under load... climbing a steep grade with 2-up or something... No matter what the compression is,... if it don't knock under load, higher octane isn't needed... JMHO... |
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Title: Re: Octane Question. Post by Gyrobob on 06/30/13 at 10:58:29 Octane does not retard ignition. A higher octane rating simply makes the mixture less susceptible to detonation,... it resists exploding all at once and tends to make the mixture burn more evenly. The higher the octane rating, the less energy is in the fuel. As long as the motor is not knocking, you should always use the lowest octane rating you can. The higher octane is there simply to allow a higher compression without detonation. This is why high-performance cars (Corvettes, WRXs, M3 BMWs, etc.) call for premium,... not because it has more energy, but because these high-compression motors need it to suppress detonation. Putting 89 or 91 or higher octane in a Savage is like putting a drag chute on your bicycle,.. just because high-speed vehicles use it doesn't mean it'll make you go faster. |
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Title: Re: Octane Question. Post by gerald.hughes on 06/30/13 at 11:15:32 Gyrobob, I am a little confused. Could you please explain the difference to me between, "retard ignition", and "makes the mixture less susceptible to detonation."? |
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Title: Re: Octane Question. Post by verslagen1 on 06/30/13 at 11:40:57 Your statement is a little bit true. Premium burns a little slower. Would you or I be able to tell... Probably not, would it retard the timing enough to tell? Don't know. |
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Title: Re: Octane Question. Post by apache snow on 06/30/13 at 12:18:19 Since the flame front travels in milliseconds that would be no. Fuel cannot advance or retard timing. Unless you claim that pre-ignition advances the timing. High octane fuel has a resistance to knock. http://auto.howstuffworks.com/fuel-efficiency/fuel-consumption/question90.htm http://www.streetrodstuff.com/Articles/Engine/Detonation/index.php Detonation Detonation is the spontaneous combustion of the end-gas (remaining fuel/air mixture) in the chamber. It always occurs after normal combustion is initiated by the spark plug. The initial combustion at the spark plug is followed by a normal combustion burn. For some reason, likely heat and pressure, the end gas in the chamber spontaneously combusts. The key point here is that detonation occurs after you have initiated the normal combustion with the spark plug. Pre-ignition Pre-ignition is defined as the ignition of the mixture prior to the spark plug firing. Anytime something causes the mixture in the chamber to ignite prior to the spark plug event it is classified as pre-ignition. The two are completely different and abnormal phenomenon. Detonation Unburned end gas, under increasing pressure and heat (from the normal progressive burning process and hot combustion chamber metals) spontaneously combusts, ignited solely by the intense heat and pressure. The remaining fuel in the end gas simply lacks sufficient octane rating to withstand this combination of heat and pressure. Detonation causes a very high, very sharp pressure spike in the combustion chamber but it is of a very short duration. If you look at a pressure trace of the combustion chamber process, you would see the normal burn as a normal pressure rise, then all of a sudden you would see a very sharp spike when the detonation occurred. That spike always occurs after the spark plug fires. The sharp spike in pressure creates a force in the combustion chamber. It causes the structure of the engine to ring, or resonate, much as if it were hit by a hammer. Resonance, which is characteristic of combustion detonation, occurs at about 6400 Hertz. So the pinging you hear is actually the structure of the engine reacting to the pressure spikes. This noise of detonation is commonly called spark knock. This noise changes only slightly between iron and aluminum. This noise or vibration is what a knock sensor picks up. The knock sensors are tuned to 6400 hertz and they will pick up that spark knock. Incidentally, the knocking or pinging sound is not the result of "two flame fronts meeting" as is often stated. Although this clash does generate a spike the noise you sense comes from the vibration of the engine structure reacting to the pressure spike. One thing to understand is that detonation is not necessarily destructive. Many engines run under light levels of detonation, even moderate levels. Some engines can sustain very long periods of heavy detonation without incurring any damage. If you've driven a car that has a lot of spark advance on the freeway, you'll hear it pinging. It can run that way for thousands and thousands of miles. Detonation is not necessarily destructive. It's not an optimum situation but it is not a guaranteed instant failure. The higher the specific output (HP/in3) of the engine, the greater the sensitivity to detonation. An engine that is making 0.5 HP/in3 or less can sustain moderate levels of detonation without any damage; but an engine that is making 1.5 HP/in3, if it detonates, it will probably be damaged fairly quickly, here I mean within minutes. |
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Title: Re: Octane Question. Post by ToesNose on 06/30/13 at 13:22:34 As far as the LS650 goes 87 Octane is all you need, anything higher is basically just wasting money :-? |
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Title: Re: Octane Question. Post by jcstokes on 06/30/13 at 15:02:08 It also depends on whether the octane is rated by the research or motor method, or a combination of both. The techies can explain this better than me. The handbook recommends a minimum of 87 octane Research plus motor divided by two method. If you can only get ethanol blended petrol don't go higher than E10. If the pump says 87 you should be ok. If you get audible pinging noises you can go up to 91. |
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Title: Re: Octane Question. Post by paulmarshall on 06/30/13 at 15:31:37 Just a quick question, What Octane would work best for a 97mm piston with a 10.5:1 ratio? |
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Title: Re: Octane Question. Post by Dave on 06/30/13 at 16:30:35 79687C6564687B7A61686565090 wrote:
You have to run premium.....91 or higher. The Savage spark advance cannot react to knock and retard the timing....so you have to buy the best you can and hope it is enough. |
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Title: Re: Octane Question. Post by paulmarshall on 06/30/13 at 16:35:12 09323F2839352E28333B36295A0 wrote:
You have to run premium.....91 or higher. The Savage spark advance cannot react to knock and retard the timing....so you have to buy the best you can and hope it is enough.[/quote] The best in NZ is 98 Octane. We have 91,95 and 98. |
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Title: Re: Octane Question. Post by Dave on 06/30/13 at 16:39:19 5F4E5A43424E5D5C474E43432F0 wrote:
You have to run premium.....91 or higher. The Savage spark advance cannot react to knock and retard the timing....so you have to buy the best you can and hope it is enough.[/quote] The best in NZ is 98 Octane. We have 91,95 and 98. [/quote] I have no idea how the NZ octane number compare to the US ones. If you have a choice between regular, mid grade and premium....use premium. Use the highest grade pump gas that is available at normal retail stations.....not race fuel. |
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Title: Re: Octane Question. Post by apache snow on 06/30/13 at 16:42:55 I believe their 91 is the same as our 87. New Zealand: 91 RON "Regular" and 95 RON "Premium" are both widely available. 98 RON is available instead of 95 RON at some service stations in larger urban areas. |
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Title: Re: Octane Question. Post by WD on 06/30/13 at 16:44:18 Different grading system NZ fuels are roughly 87, 89, 91-93 U.S.A. method. Savage will safely burn USA spec 85 octane. Some parts of the mid-west used to sell 85, 87, 89, my 1998 model was quite happy running the 85 octane "paint brush cleaner" as fuel. About E12-15 range. Want to make your bike really happy? make friends with a crop duster who buys his av-gas in drums. It is hi octane LEADED fuel, real gasoline, not the modern on road imitation stuff that ruins older engines. |
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Title: Re: Octane Question. Post by paulmarshall on 06/30/13 at 16:45:25 665D5047565A41475C545946350 wrote:
You have to run premium.....91 or higher. The Savage spark advance cannot react to knock and retard the timing....so you have to buy the best you can and hope it is enough.[/quote] The best in NZ is 98 Octane. We have 91,95 and 98. [/quote] I have no idea how the NZ octane number compare to the US ones. If you have a choice between regular, mid grade and premium....use premium. Use the highest grade pump gas that is available at normal retail stations.....not race fuel.[/quote] OK I will use the highest Octane. If I had a stock piston would I still be wanting to use the higher octane? |
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Title: Re: Octane Question. Post by apache snow on 06/30/13 at 16:46:34 New Zealand uses the RON method while The US uses AKI. http://en.wikipedia.org/wiki/Octane_rating |
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Title: Re: Octane Question. Post by paulmarshall on 06/30/13 at 16:58:53 6879686A616C7A67667E090 wrote:
United States: in the US octane rating is displayed in AKI. In the Rocky Mountain (high elevation) states, 85 AKI (90 RON) is the minimum octane, and 91 AKI (95 RON) is the maximum octane available in fuel. I just copied and pasted this from the article apache snow posted above. Is 91 AKI really your highest Octane? |
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Title: Re: Octane Question. Post by paulmarshall on 06/30/13 at 17:00:32 So our 98 RON would be 94 AKI if you guys had it? |
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Title: Re: Octane Question. Post by apache snow on 06/30/13 at 17:36:39 We have 93 in a lot of places. |
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Title: Re: Octane Question. Post by Gyrobob on 06/30/13 at 17:36:45 2B293E2D20286224392B24293F4C0 wrote:
Retards ignition = starts the burning later Making it less susceptible to detonation = once it starts burning, it will not be so prone to exploding (detonating). |
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Title: Re: Octane Question. Post by Gyrobob on 06/30/13 at 18:10:59 Premium doesn't burn any slower than regular. This is an old wives' tales spread by the likes of wikianswers, cha cha, ask Jeeves, yahoo answers, most auto and cycle and boat forums, etc. Premium is less susceptible to detonation because of octane additives,.. it has nothing to do with burn rate. For one thing the burn rate of all the fuels available to Savage riders is for all practical purposes, identical. If there is a diff, it would be measured in nanoseconds,.. nothing we would ever notice. If you research what is said by engineers, rather than folks like us blathering about on forums, you'll find statements like this from Jim Wurth from Sunoco Race Fuels. He explains, "A perfect example is Sunoco Maximal, which is our fastest burning fuel, and one of Sunoco's highest octane fuels at 116 (R+M)/2. A lot of Pro Stock teams rely on Maximal for those sub-seven second runs. When they are turning 9,000 rpm or more, the fuel has to burn pretty quickly to achieve complete combustion." The old saw about premium burning slower is one of those "everyone knows" kinds of things, such as in the 1500s "everyone knows the earth is flat" or today, "Everyone knows whole grains are healthy." That said,... it is mostly irrelevant. In any event, here is what matters to us: -- 87 octane is marvy in a stock Savage running properly. -- using more than 87 in a stock Savage running properly is a waste of money. -- using more than 87 in a stock Savage running properly won't hurt the motorcycle any, just your wallet. -- using more than 87 in a stock Savage running properly will not cause any increase in performance or do anything better for the motor. If there is any change at all (unlikely), it will be a decrease in performance. -- if you increase the compression ratio or advance the timing or both, use the highest octane you can get. |
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Title: Re: Octane Question. Post by apache snow on 06/30/13 at 18:44:50 I havn't done much reaserch on the burn rates of different octanes and probably won't as I am well aware of what to run in my motorcycle and automobiles but your perfect example of a 116 octane race fuel designed to run in a 7 second prostock being compared to regular every day 87 federal spec octane fuel is a bit of a streatch. :-? Burn rate of pump automotive gasoline is regulated by US govt and standardised pretty much across the board. High octane simply has a higher resistance to spontaneous combustion than regular gasoline has. Later on in the same article he said this.. What is it that makes race gas so different? What's it made of? Sunoco tells us their GT PLUS 104 octane unleaded race gas is only 15-20 percent traditional gasoline, and about 85 percent additives! Actually there are about 120 different chemicals in GT PLUS. One reason it isn't street legal is the high oxygen content. The EPA requires that the oxygen content of a street legal fuel cannot exceed 2.9 percent. GT PLUS is about 3.5 percent oxygen. This fuel is light in weight at only 6.14 lbs-per-gallon. The high oxygen content improves the octane, and when the induction system is properly calibrated, this fuel will help make additional horsepower. The high oxygen content has a supercharging effect, since 3.5 percent oxygen is the equivalent to about 17 percent more air. Different fuels can actually alter horsepower 5-to-10 percent or more. |
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Title: Re: Octane Question. Post by Serowbot on 06/30/13 at 18:52:37 754B405D505D50320 wrote:
That's funny... my Ninja redllined at 11,000+rpm, and it ran fine on regular gas... :-/... |
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Title: Re: Octane Question. Post by Gyrobob on 06/30/13 at 19:30:16 Be that as it may, burn rate diff (be it faster or slower) between premium and regular is so small, it is a non-issue for Savage folks bandying about on stock Savages. For a stock Savage motor running properly, anything other than 87 is a waste of money because it will make no difference in performance, temp, mileage, power, longevity, sound, smoothness, smell, or handsomeness. The only actual difference it would make is having less money to spend on yourself (or your current wife) after each gas purchase. |
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Title: Re: Octane Question. Post by Gyrobob on 06/30/13 at 19:34:02 5543544951444952260 wrote:
That's funny... my Ninja redllined at 11,000+rpm, and it ran fine on regular gas... :-/...[/quote] Your ninja had quite a different set of operating conditions than a 2,000hp 6.9 second pro stock vehicle. the situations are not analogous |
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Title: Re: Octane Question. Post by Gyrobob on 06/30/13 at 19:37:16 263726242F2234292830470 wrote:
Not a "streatch" at all. The only point being made is that octane, and therefore detonation suppression, has nothing at all to do with burn rate,... which, for the fuels available to us,... is pretty much irrelevant since the burn rates are all the same. |
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Title: Re: Octane Question. Post by apache snow on 06/30/13 at 19:41:12 No the fuel you used as an example is designed with a much faster burn rate for racing applications than is allowed in federal spec fuel and has nothing to do with our motorcycles. I understand the burn rates of pump gas and what gives it its resistance to knock. |
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Title: Re: Octane Question. Post by jcstokes on 06/30/13 at 21:05:08 Paul Marshall, the same thing about avgas that applies in the States applies here. You would need to be friendly with a pilot, or join a motorcycle club to get avgas. As far as I'm aware the stuff is low lead petrol of 100 to 110 octane and don't ask me if it's RON, MON, AKI or a combo, it's what is also called race gas here. 95 or 98 pump petrol, which aviators call MOGAS should be ok for you. |
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Title: Re: Octane Question. Post by paulmarshall on 06/30/13 at 21:17:54 5B5242455E5A5442310 wrote:
Cheers for that. :) |
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Title: Re: Octane Question. Post by Gyrobob on 07/01/13 at 07:22:54 263726242F2234292830470 wrote:
Precisely the point. Burn rate (and the infinitesimally small differences of various grades therein) has nothing to do with our motorcycles. |
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Title: Re: Octane Question. Post by Gyrobob on 07/01/13 at 07:24:25 686171766D696771020 wrote:
"As far as I'm aware the stuff is low lead petrol" Everything is relative. Low-lead in aviation gas means huge lead in auto gas. |
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Title: Re: Octane Question. Post by Pine on 07/01/13 at 07:39:18 Avgas: I tired to buy some once.. just out at the airport. They said it was not legal for use in automobiles (I wanted it for my '65 tbird). Then they said be there at 6pm on Friday night, and bring cash. $5.75 per gal. Never did it. Gotta love the car nuts! |
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Title: Re: Octane Question. Post by Dave on 07/01/13 at 08:07:36 142D2A21302B36440 wrote:
Avgas is not legal for use in street driven cars.....as there is no Road Use Tax included in the sales. Also leaded fuel is not legal for use in any car with a catalytic converter....the lead fouls the converter and makes it non-functional. I had a horrible time trying to buy it for use in an antique car once when I went to a major Cincinatti airport. I was buying it to use in a 1906 car as the new ethanol fuel does not vaporize well in updraft carbs and Avgas does a better job. Since then I found a small county airport that is not staffed and they have a fuel pump at the airport that uses your credit card....you just pump you own fuel without any problems or hassles. Avgas does not run all that well in an engine that is not jetted to run it. I used it in my chainsaws for a year and the carbs all had to be set to run leaner.....without adjustment to the carbs they ran richer than on pump gas. You can't use it in fuel injected motors as it will foul the oxygen sensor. Avgas 100LL is not made the same way as auto fuels. Instead of refining crude oil......Avgas is made by blending refined petroleum chemicals back together to make fuel. Avgas 100LL is 70% Alkylate, 15% Isopentane, 15% Toluene...the rest is additives that include dye and antioxidant. Avgas 100LL is not low lead compared to auto fuels.....it has 2 grams per gallon which is equal to the most lead that High Test automotive fuels used. The Low Lead name for this fuel relates to the fact that some of the higher grade Aviation fuels used to have 4 and 6 grams per gallon. There is no need to run lead or Avgas in the Savage. I do keep a small amount of Avgas 100LL in my emergency generator. The fuel never goes bad and does not leave any varnish behind. When the fuel evaporates it leaves nothing behind, and it does not corrode anything. When I need the generator I know that it will start.....if I need to run it for a long period until the power is restored I just use pump gas. Before I put the generator away I make sure it has Avgas in the tank and the fuel is shut off and the float bowl is empty. For our Savage pump gas does jst fine: Regular if the bike has the stock piston. Premium if you have installed a Wiseco. |
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Title: Re: Octane Question. Post by Gyrobob on 07/01/13 at 08:41:52 Dave said: Four our Savage pump gas does jst fine: Regular if the bike has the stock piston. Premium if you have installed a Wiseco. Zackly. 'cep for the four |
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Title: Re: Octane Question. Post by Dave on 07/01/13 at 08:48:40 7749425F525F52300 wrote:
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