Using 93 octane in the mazda 3
12-16-2009, 07:16 AM
#27
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Yeah! And good beer money. My wife has a 4 cyl Tribute and been running on regular with no problems. My wife has a definite understanding on how important Beer money is. Also cigars.
12-16-2009, 08:52 AM
#28
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thanks for the input everyone, sorry i havent checked on htis in awhile. since posting I have, at different times, considered ALL options presented in your responses but have yet to folow through with any of them...maybe i will just do a combination of each. another question though...this morining i started her car for her while she was getting ready, when i did this i turned on her rear window defroster and her cab lights dimmed a little...i am pretty sure it was normal. I mentioned it to her later and she now thinks there is a major problem with her car and it needs to be taken into the shop....it it really that big of a deal?
12-16-2009, 09:31 AM
#30
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I mean seriously how much money are you saving by running a lower grade fuel? What $2.00 a fill-up. I mean when gas was over $4.00 a gallon and I was driving 70 miles a day it was a bitch running 93 but......... Let her put what she wants, at least she is thinking about her car.
And.... Not that it is a huge issue for new cars but premium fuel does generally have more detergents than regular gas.
And.... Not that it is a huge issue for new cars but premium fuel does generally have more detergents than regular gas.
Last edited by 9krpmrx8; 12-16-2009 at 09:36 AM.
12-18-2009, 01:23 AM
#31
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12-18-2009, 02:15 AM
#32
I mean seriously how much money are you saving by running a lower grade fuel? What $2.00 a fill-up. I mean when gas was over $4.00 a gallon and I was driving 70 miles a day it was a bitch running 93 but......... Let her put what she wants, at least she is thinking about her car.
And.... Not that it is a huge issue for new cars but premium fuel does generally have more detergents than regular gas.
And.... Not that it is a huge issue for new cars but premium fuel does generally have more detergents than regular gas.
the savings is 832 bucks. or say a really good set of tires.
but again i always use 93 for track events, and known hard driving..
beers
12-18-2009, 09:37 AM
#33
Administrator
nvrfalter being one of them and apparently this person in the next quote
this is such a jumble of incorrect and partially correct statements that I find it difficult to keep my head from exploding.
lets get this out of the way first-
OCTANE IS NOT A MEASURE OF THE SPEED AT WHICH THE FUEL BURNS. Octane is the anti-knock index. Knock occurs when as yet unburned end gasses in the combustion chamber ignite BEFORE the propagating flame-front reaches them. Octane says nothing about the speed of the flame front propagation.
Higher Octane fuel doesn't have an "albeit more concentrated combustion" than lower octane fuel. the "concentration" is a factor of the engine not the fuel.
I'm not sure what you mean by purpose built engine. Clearly there are an incredible large amount of high compression engines on the road that need either fuel with a high anti-knock rating or very good anti-knock systems. so possibly that's what you mean. So if you meant high compression engines then i guess were right. it seemed more like you were saying specialty engines.
Then you went on pretty good until you wrote "cheap fuels" which muddles it. If by cheap you mean "less expensive" than a higher octane fuel than that is correct. But often cheap is used to mean less desirable and you cant judge fuel that way. If your engine requires high octane it s better to by the off brand high octane than the more desirable brand's lower octane.
Hmm the next paragraph is pretty good and i dont feel like picking the nits in there.
Knock sensors don't retard timing if use use a lower grade of fuel. They cannot detect your fuel grade they are acoustic sensors and actually listen for the noise of knock. The pcm retards timing if the engine experiences knock heard by the knock sensors. Knock can occur for other reasons besides fuel grade.
Then you went into that "however compression ratio and volumetric efficiency" stuff and the "however" links it to your knock sensor line but it has no clear connection. what does the volumetric efficiency as you have described have to do with the workings of the knock sensor in the first sentence of that paragraph?
Then in your summation you use that purpose built and "cheaper fuel" again in the first sentence. And the last sentence you equate octane with the amount of cleaning detergents in the fuel. it simply has nothing to do with each other. That totally depends on the company making the fuel. Octane level is not a measure of detergents. Some companies include less detergent in the costlier grades to improve their margin. Others include the same percentages in each grade.
Tell her:
Higher octane 93 fuel actually burns SLOWER than 87 octane fuels. Since gasoline is a mixture of several different hydrocarbons that burn at different rates, the cheaper lower octane mixture will start burning faster but with a less concentrated BOOM.
With a higher octane fuel, the slower burning, albeit more concentrated combustion, allows for a more controlled explosion. This in itself doesn't necessarily yield more power or better economy by itself but it can be exploited to do so assuming you have a purpose built engine.
For a purpose built piston engine this means higher compression ratios starting at 10:1. Higher compressions means higher squish and hence more torque IF you can protect against early detonation which becomes a problem since higher cylinder pressures also mean more heat. This heat contributes to early detonation on cheap fuels due to a lower ignition temp. Therefore, the use of a higher octane fuel is required with it's slower burning but more concentrated combustion.
There are many other factors affecting an engines octane needs: Advanced spark timing, short stroke vs long strong relative to bore sizing, cam timing: lift, duration, overlap; small bore vs large bore, cylinder filling, swirl etc etc with compression ratio and ignition timing being the main factors.
Today, all cars come with a knock sensor that senses pre ignition signaling the computer to retard timing should you use a lower grade of fuel than your car requires. However, compression ratios are fixed but the actual volumetric efficiency (or amount of air the engine actually ingests) often improves at higher RPM's (depending upon tuning) or with the addition of a turbo. Just because your cylinder holds 100 cc's of air doesn't mean it ingests 100 cc's at every intake stroke. This volumetric efficiency changes over the RPM band.
So really it is really comes down to this: If you have the purpose built engine that requires a higher octane fuel, then your car may drive better than if you used a lower grade, cheaper fuel. But if your car doesn't need a higher octane fuel, aside from extra cleaning detergents, you might actually find worse gas mileage off.
For the RX-8, I find mid grade fuel to be the best for me here in PA.
Higher octane 93 fuel actually burns SLOWER than 87 octane fuels. Since gasoline is a mixture of several different hydrocarbons that burn at different rates, the cheaper lower octane mixture will start burning faster but with a less concentrated BOOM.
With a higher octane fuel, the slower burning, albeit more concentrated combustion, allows for a more controlled explosion. This in itself doesn't necessarily yield more power or better economy by itself but it can be exploited to do so assuming you have a purpose built engine.
For a purpose built piston engine this means higher compression ratios starting at 10:1. Higher compressions means higher squish and hence more torque IF you can protect against early detonation which becomes a problem since higher cylinder pressures also mean more heat. This heat contributes to early detonation on cheap fuels due to a lower ignition temp. Therefore, the use of a higher octane fuel is required with it's slower burning but more concentrated combustion.
There are many other factors affecting an engines octane needs: Advanced spark timing, short stroke vs long strong relative to bore sizing, cam timing: lift, duration, overlap; small bore vs large bore, cylinder filling, swirl etc etc with compression ratio and ignition timing being the main factors.
Today, all cars come with a knock sensor that senses pre ignition signaling the computer to retard timing should you use a lower grade of fuel than your car requires. However, compression ratios are fixed but the actual volumetric efficiency (or amount of air the engine actually ingests) often improves at higher RPM's (depending upon tuning) or with the addition of a turbo. Just because your cylinder holds 100 cc's of air doesn't mean it ingests 100 cc's at every intake stroke. This volumetric efficiency changes over the RPM band.
So really it is really comes down to this: If you have the purpose built engine that requires a higher octane fuel, then your car may drive better than if you used a lower grade, cheaper fuel. But if your car doesn't need a higher octane fuel, aside from extra cleaning detergents, you might actually find worse gas mileage off.
For the RX-8, I find mid grade fuel to be the best for me here in PA.
lets get this out of the way first-
OCTANE IS NOT A MEASURE OF THE SPEED AT WHICH THE FUEL BURNS. Octane is the anti-knock index. Knock occurs when as yet unburned end gasses in the combustion chamber ignite BEFORE the propagating flame-front reaches them. Octane says nothing about the speed of the flame front propagation.
Higher Octane fuel doesn't have an "albeit more concentrated combustion" than lower octane fuel. the "concentration" is a factor of the engine not the fuel.
I'm not sure what you mean by purpose built engine. Clearly there are an incredible large amount of high compression engines on the road that need either fuel with a high anti-knock rating or very good anti-knock systems. so possibly that's what you mean. So if you meant high compression engines then i guess were right. it seemed more like you were saying specialty engines.
Then you went on pretty good until you wrote "cheap fuels" which muddles it. If by cheap you mean "less expensive" than a higher octane fuel than that is correct. But often cheap is used to mean less desirable and you cant judge fuel that way. If your engine requires high octane it s better to by the off brand high octane than the more desirable brand's lower octane.
Hmm the next paragraph is pretty good and i dont feel like picking the nits in there.
Knock sensors don't retard timing if use use a lower grade of fuel. They cannot detect your fuel grade they are acoustic sensors and actually listen for the noise of knock. The pcm retards timing if the engine experiences knock heard by the knock sensors. Knock can occur for other reasons besides fuel grade.
Then you went into that "however compression ratio and volumetric efficiency" stuff and the "however" links it to your knock sensor line but it has no clear connection. what does the volumetric efficiency as you have described have to do with the workings of the knock sensor in the first sentence of that paragraph?
Then in your summation you use that purpose built and "cheaper fuel" again in the first sentence. And the last sentence you equate octane with the amount of cleaning detergents in the fuel. it simply has nothing to do with each other. That totally depends on the company making the fuel. Octane level is not a measure of detergents. Some companies include less detergent in the costlier grades to improve their margin. Others include the same percentages in each grade.
12-18-2009, 12:41 PM
#35
I don't think this forum as a whole is in any position to mock someone's understanding of octane rating. I'm willing to bet at least 80% of the US could not properly explain the meaning and impact of octane rating. This forum, even as a car forum, is not much better. And really, it's not that important to know. If you put gas in your stock car and it runs fine, the worst case is you waste a few hundred bucks a year. Now most people heavily invested in performance are going to run a ~93 octane rating whether they understand it or not. They just think it's better. The only real issue is when you put a low octane into an application where you actually need the margin against knock/detonation.
Interesting read:
http://www.motorcycle.com/how-to/wre...-gas-3417.html
http://www.motorcycle.com/how-to/wre...tion-3420.html
Interesting read:
http://www.motorcycle.com/how-to/wre...-gas-3417.html
http://www.motorcycle.com/how-to/wre...tion-3420.html
12-18-2009, 01:56 PM
#36
Administrator
you are right. alll of the people who mocked but didn't provide the correct info weren't helping.
but are you suggesting that because "80%" of the country or even most of this forum don't understand that we should stop correcting bad information when its given? I would hope that people heavily invested in performance would like to know the facts about when they are wasting their time effort and money or not.
Maybe we should have just let people go ahead and purchase the K&N version 1 without telling them they were wasting their money and explaining why?
anyway the links you posted to articles about fuel and knock are excellent
but are you suggesting that because "80%" of the country or even most of this forum don't understand that we should stop correcting bad information when its given? I would hope that people heavily invested in performance would like to know the facts about when they are wasting their time effort and money or not.
Maybe we should have just let people go ahead and purchase the K&N version 1 without telling them they were wasting their money and explaining why?
anyway the links you posted to articles about fuel and knock are excellent
12-18-2009, 02:08 PM
#37
you are right. alll of the people who mocked but didn't provide the correct info weren't helping.
but are you suggesting that because "80%" of the country or even most of this forum don't understand that we should stop correcting bad information when its given? I would hope that people heavily invested in performance would like to know the facts about when they are wasting their time effort and money or not.
Maybe we should have just let people go ahead and purchase the K&N version 1 without telling them they were wasting their money and explaining why?
anyway the links you posted to articles about fuel and knock are excellent
but are you suggesting that because "80%" of the country or even most of this forum don't understand that we should stop correcting bad information when its given? I would hope that people heavily invested in performance would like to know the facts about when they are wasting their time effort and money or not.
Maybe we should have just let people go ahead and purchase the K&N version 1 without telling them they were wasting their money and explaining why?
anyway the links you posted to articles about fuel and knock are excellent
I'm 100% all for myth debunking.
12-22-2009, 07:32 PM
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nvrfalter being one of them and apparently this person in the next quote
this is such a jumble of incorrect and partially correct statements that I find it difficult to keep my head from exploding.
lets get this out of the way first-
OCTANE IS NOT A MEASURE OF THE SPEED AT WHICH THE FUEL BURNS. Octane is the anti-knock index. Knock occurs when as yet unburned end gasses in the combustion chamber ignite BEFORE the propagating flame-front reaches them. Octane says nothing about the speed of the flame front propagation.
Higher Octane fuel doesn't have an "albeit more concentrated combustion" than lower octane fuel. the "concentration" is a factor of the engine not the fuel.
I'm not sure what you mean by purpose built engine. Clearly there are an incredible large amount of high compression engines on the road that need either fuel with a high anti-knock rating or very good anti-knock systems. so possibly that's what you mean. So if you meant high compression engines then i guess were right. it seemed more like you were saying specialty engines.
Then you went on pretty good until you wrote "cheap fuels" which muddles it. If by cheap you mean "less expensive" than a higher octane fuel than that is correct. But often cheap is used to mean less desirable and you cant judge fuel that way. If your engine requires high octane it s better to by the off brand high octane than the more desirable brand's lower octane.
Hmm the next paragraph is pretty good and i dont feel like picking the nits in there.
Knock sensors don't retard timing if use use a lower grade of fuel. They cannot detect your fuel grade they are acoustic sensors and actually listen for the noise of knock. The pcm retards timing if the engine experiences knock heard by the knock sensors. Knock can occur for other reasons besides fuel grade.
Then you went into that "however compression ratio and volumetric efficiency" stuff and the "however" links it to your knock sensor line but it has no clear connection. what does the volumetric efficiency as you have described have to do with the workings of the knock sensor in the first sentence of that paragraph?
Then in your summation you use that purpose built and "cheaper fuel" again in the first sentence. And the last sentence you equate octane with the amount of cleaning detergents in the fuel. it simply has nothing to do with each other. That totally depends on the company making the fuel. Octane level is not a measure of detergents. Some companies include less detergent in the costlier grades to improve their margin. Others include the same percentages in each grade.
this is such a jumble of incorrect and partially correct statements that I find it difficult to keep my head from exploding.
lets get this out of the way first-
OCTANE IS NOT A MEASURE OF THE SPEED AT WHICH THE FUEL BURNS. Octane is the anti-knock index. Knock occurs when as yet unburned end gasses in the combustion chamber ignite BEFORE the propagating flame-front reaches them. Octane says nothing about the speed of the flame front propagation.
Higher Octane fuel doesn't have an "albeit more concentrated combustion" than lower octane fuel. the "concentration" is a factor of the engine not the fuel.
I'm not sure what you mean by purpose built engine. Clearly there are an incredible large amount of high compression engines on the road that need either fuel with a high anti-knock rating or very good anti-knock systems. so possibly that's what you mean. So if you meant high compression engines then i guess were right. it seemed more like you were saying specialty engines.
Then you went on pretty good until you wrote "cheap fuels" which muddles it. If by cheap you mean "less expensive" than a higher octane fuel than that is correct. But often cheap is used to mean less desirable and you cant judge fuel that way. If your engine requires high octane it s better to by the off brand high octane than the more desirable brand's lower octane.
Hmm the next paragraph is pretty good and i dont feel like picking the nits in there.
Knock sensors don't retard timing if use use a lower grade of fuel. They cannot detect your fuel grade they are acoustic sensors and actually listen for the noise of knock. The pcm retards timing if the engine experiences knock heard by the knock sensors. Knock can occur for other reasons besides fuel grade.
Then you went into that "however compression ratio and volumetric efficiency" stuff and the "however" links it to your knock sensor line but it has no clear connection. what does the volumetric efficiency as you have described have to do with the workings of the knock sensor in the first sentence of that paragraph?
Then in your summation you use that purpose built and "cheaper fuel" again in the first sentence. And the last sentence you equate octane with the amount of cleaning detergents in the fuel. it simply has nothing to do with each other. That totally depends on the company making the fuel. Octane level is not a measure of detergents. Some companies include less detergent in the costlier grades to improve their margin. Others include the same percentages in each grade.
1) First point, I never said that the octane rating of a fuel was technnically defined by the speed at which it burns. However, it is a true fact that higher octane fuels do burn slower and so for ease of understanding how different octane fuels function, I chose to focused on the speed of combustion in my explanation. See here for a dissertation of what I'm talking about: http://www.bajajusa.com/High%20Octane.htm
2) Second point, regarding my comment that higher octane fuels allow for a more concentration explosion----Here again I'm talking about the burn rate of the fuel, not the compression ratio which is a function of the engine. What we really want is a very rapid burn of the fuel, not an explosion. And we want the burning of the fuel to take place while the piston is in a better position to convert this pressure into productive work, like on its way down. Think of this burning as a very fast "push" on the top of the piston. This is what I'm talking about a more concentrated BOOM. A lower octane fuel might start burning too early when the piston is still rising to top dead center and against the piston.
3) By purpose built engines, yes, I'm talking about engines built with high compression ratios with advanced timing that require high octane fuels. These engines are purpose built to take advantage of high octane fuels (including alcohol which is a high octane, slow burning fuel). Most engines are designed to run on 87 Octane, not the other way around. A Corvette engine is purpose built for 93 octane.
4) Okay, maybe my description of "cheap" fuels might have muddied the water a little bit but I think we all know that 87 is less expensive than 93 and hence "cheaper".
5) I don't think I explained really how a knock sensor worked but you did. I thought it was enough to explain that in theory a knock sensor retarded timing if using a lower octane fuel caused any problems.
6) I only mentioned volumetric efficiency because a turbo'ed engine NOT in boost will idle perfectly fine with a lower octane fuel. But the moment you put it in boost, your octane requirement becomes more sensitive. Cam shaft timing also affects cylinder filling over rpm. I guess this supports your assertion that some high compression engines may run perfectly fine with lower octane fuels---But this is going beyond the scope of the discussion and maybe I shouldn't have mentioned it.
7) As a general rule, higher octane gasolines tend to have more cleaning detergents. However, I agree that this is not tied to the definition of octane.
12-22-2009, 08:05 PM
#40
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If anything, since the higher octane fuel will ignite at a higher temperature, it will lead to premature engine part failures, since her engine was not designed for that fuel.
12-22-2009, 08:12 PM
#41
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One of the best same-car examples I ran into that can be applied for regular vs Premium is the Miata.
Miatas run on 87 octane, they were designed to. However, one of the most common mods that people do to Miatas is advance the timing 14(?) degrees. This gets a boost of power, however it also leads to a heavy risk of detonation, and thus requires a change to 93 to prevent it detonating.
Miatas run on 87 octane, they were designed to. However, one of the most common mods that people do to Miatas is advance the timing 14(?) degrees. This gets a boost of power, however it also leads to a heavy risk of detonation, and thus requires a change to 93 to prevent it detonating.
12-22-2009, 08:29 PM
#42
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Octane does not tell you anything about flame speed.
http://www.faqs.org/faqs/autos/gasoline-faq/part3/
6.3
http://www.faqs.org/faqs/autos/gasoline-faq/part3/
6.3
The antiknock ability is related to the "autoignition temperature" of the
hydrocarbons. Antiknock ability is _not_ substantially related to:-
1. The energy content of fuel, this should be obvious, as oxygenates have
lower energy contents, but high octanes.
2. The flame speed of the conventionally ignited mixture, this should be
evident from the similarities of the two reference hydrocarbons.
Although flame speed does play a minor part, there are many other factors
that are far more important. ( such as compression ratio, stoichiometry,
combustion chamber shape, chemical structure of the fuel, presence of
antiknock additives, number and position of spark plugs, turbulence etc.)
Flame speed does not correlate with octane.
Read more: http://www.faqs.org/faqs/autos/gasol...#ixzz0aTW7QfV7
hydrocarbons. Antiknock ability is _not_ substantially related to:-
1. The energy content of fuel, this should be obvious, as oxygenates have
lower energy contents, but high octanes.
2. The flame speed of the conventionally ignited mixture, this should be
evident from the similarities of the two reference hydrocarbons.
Although flame speed does play a minor part, there are many other factors
that are far more important. ( such as compression ratio, stoichiometry,
combustion chamber shape, chemical structure of the fuel, presence of
antiknock additives, number and position of spark plugs, turbulence etc.)
Flame speed does not correlate with octane.
Read more: http://www.faqs.org/faqs/autos/gasol...#ixzz0aTW7QfV7
12-22-2009, 09:29 PM
#43
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Although they are independent of each other, flame speed and octane number both impact the amount of power that an engine will develop. To get maximum power from an engine, one must have a gasoline with adequate flame speed (faster is always better), and adequate octane quality to support the combustion process.
Technically by definition there is no correlation between octane rating and flame speed because there exists racing fuels that are high octane but with a fast burn rate. However, the de facto reality is that unless you're running leaded fuels (which I'm pretty sure you're not), the opposite is usually true, i.e., the higher the octane, the slower the flame speed. For street legal street fuels, it's better to think of octane and flame speed as correlated.
FYI: High octane racing fuels typically have a higher oxygen content allowing for a faster burn rate. However, the EPA limits oxygen content to 2.9% making the 3.5% racing fuels illegal for street use.
Read more: http://www.nsxprime.com/FAQ/Miscella...lAdditives.htm
Technically by definition there is no correlation between octane rating and flame speed because there exists racing fuels that are high octane but with a fast burn rate. However, the de facto reality is that unless you're running leaded fuels (which I'm pretty sure you're not), the opposite is usually true, i.e., the higher the octane, the slower the flame speed. For street legal street fuels, it's better to think of octane and flame speed as correlated.
FYI: High octane racing fuels typically have a higher oxygen content allowing for a faster burn rate. However, the EPA limits oxygen content to 2.9% making the 3.5% racing fuels illegal for street use.
Read more: http://www.nsxprime.com/FAQ/Miscella...lAdditives.htm
Last edited by b'Eight'; 12-22-2009 at 10:18 PM.
12-23-2009, 12:19 AM
#44
Administrator
http://www.whitfieldoil.com/www/docs...race-fuel.html
http://www.faqs.org/faqs/autos/gasol.../preamble.html
http://www.rockettbrand.com/techsupp...ationships.pdf
http://cbrworld.net/forums/post/922.aspx
http://www.trx450r.org/forum/index.php?showtopic=72357
http://www.elektro.com/~audi/fuel/Fuel.definitions
http://cranecams.com/?show=newsLetters&no=193
http://books.google.com/books?id=had...gbs_navlinks_s
http://www.mrtperformance.com/perfor...ver3-FINAL.pdf.
i could go on
12-23-2009, 01:36 PM
#46
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Unleaded 93 burns slower than 91 which burns slower than 87. Again, the de facto reality is that for street fuels, octane and flame speed are correlated. If you're talking about leaded gas and high oxygenated racing fuels (both which cannot be legally run on the street), then as I stated, technically the correlation is not true. There is the real world, and then there is the real world.
The links previous links zoom44 provides were to sell racing fuel. Of course they want to advertise that octane rating and flame speed aren't correlated.
The links previous links zoom44 provides were to sell racing fuel. Of course they want to advertise that octane rating and flame speed aren't correlated.
Last edited by b'Eight'; 12-23-2009 at 01:54 PM.
12-23-2009, 01:39 PM
#47
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Shot in the dark, but what the heck.
Anybody with a 5-door Mazda3 that wants or needs a front mask. I got one pretty cheap! Came with my daughters 05 and she's not using it.
Anybody with a 5-door Mazda3 that wants or needs a front mask. I got one pretty cheap! Came with my daughters 05 and she's not using it.
12-23-2009, 02:37 PM
#48
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Another way of looking at this problem is through ignition timing. The general rule states that the higher the compression ratio, the higher the octane fuel you need and hence more ignition timing. If there was no de facto correlation between octane rating and flame speed, why advance the timing??? Is the rule of thumb not true??
An analogy might help. The law of gravity says that all things fall to the ground. Then someone discovers the helium balloon and up it goes and doesn't fall to the earth. So we revise the law of gravity to mean, anything heavier than air falls to the ground. However, is it incorrect to say that all things fall to ground? In my world, the law holds true 99% of the time. Is there a correlation?? You tell me.
It's the same with compression ratios and volumetric efficiency. Why in a supercharged engine would you decrease the compression ratio? Because the supercharger increases volumetric efficiency over 1:1. So with a lower compression ratio, would you use a lower octane fuel? Of course not.
Rules of thumb are rules of thumb. They hold true over certain conditions. As a rule of thumb, higher octane gasolines have slower flame speed and require more ignition timing. If you are running a highly oxygenated, leaded fuel, I'm sure you can retard the timing more than you would otherwise suspect.
Racing fuel companies stress and advertise that flame speed and octane rating are technically independent because they want to sell more race fuel.
Alcohol is another high octane, high flame speed fuel. However, unless your car is purpose built to run alcohol it means **** and therefore the rule of thumb doesn't apply.
An analogy might help. The law of gravity says that all things fall to the ground. Then someone discovers the helium balloon and up it goes and doesn't fall to the earth. So we revise the law of gravity to mean, anything heavier than air falls to the ground. However, is it incorrect to say that all things fall to ground? In my world, the law holds true 99% of the time. Is there a correlation?? You tell me.
It's the same with compression ratios and volumetric efficiency. Why in a supercharged engine would you decrease the compression ratio? Because the supercharger increases volumetric efficiency over 1:1. So with a lower compression ratio, would you use a lower octane fuel? Of course not.
Rules of thumb are rules of thumb. They hold true over certain conditions. As a rule of thumb, higher octane gasolines have slower flame speed and require more ignition timing. If you are running a highly oxygenated, leaded fuel, I'm sure you can retard the timing more than you would otherwise suspect.
Racing fuel companies stress and advertise that flame speed and octane rating are technically independent because they want to sell more race fuel.
Alcohol is another high octane, high flame speed fuel. However, unless your car is purpose built to run alcohol it means **** and therefore the rule of thumb doesn't apply.
Last edited by b'Eight'; 12-23-2009 at 02:39 PM.
12-23-2009, 03:18 PM
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In this situation I recommend getting some nice 14:1 CR pistons, forged rods, titanium retainers/springs, etc. and a nice tune with engine management for 93 octane
Then pump it full of 93-octane and let it rip the next time your girl is in the car and just turn to her and say
"Wow baby you were right, this 93 octane really makes all the difference!"
OR
"Wow you were right! I bet we could get the CR even higher with 100 octane race fuel! We should start using that"
Then pump it full of 93-octane and let it rip the next time your girl is in the car and just turn to her and say
"Wow baby you were right, this 93 octane really makes all the difference!"
OR
"Wow you were right! I bet we could get the CR even higher with 100 octane race fuel! We should start using that"
12-23-2009, 03:30 PM
#50
Knock/Ping are generally caused by sound wave reverberation causing localized high pressure spots. Sound waves travel at the speed of sound which in a foot race rapes flame front speed. If you have a fuel that is of say 87 octane, it it most susceptible to these tendencies. You use a more conservative timing to delay the pressure waves to later in the cycle. If you use a higher octane (less prone to knock) fuel, you can run the fuel closer to the ideal maximum ignition point. Octane of a fuel can be increased with additives that only reduce knock/ping and do not affect flame front speed or internal energy content. Additionally, tumble and swirl greatly augment the rate of combustion well beyond the speed of the flame front. Think of it as running forward while on a bus.
Combustion energy of the fuel (which generally even) and mass/initial temperature of the agents determines your net final temperature. Raising octane does not raise the heat generated its self.
Ultimately, the only thing octane means is the propensity to knock/ping. It is a measurement of knock/ping. A company can obtain that end result number almost any chemical way that works for them minus whatever regulations there are.
Combustion energy of the fuel (which generally even) and mass/initial temperature of the agents determines your net final temperature. Raising octane does not raise the heat generated its self.
Ultimately, the only thing octane means is the propensity to knock/ping. It is a measurement of knock/ping. A company can obtain that end result number almost any chemical way that works for them minus whatever regulations there are.