im using the good gas
#21
08-13-2008 | 05:01 PM
Member
Joined: Feb 2007
Posts: 689
From: Alabanana
Right-O
Lowest I've paid lately was $3.59 last weekend in LA (Lower Alabama).
#22
08-13-2008 | 05:27 PM
And things have come to a pretty sad place when we are all jubilant about gas that costs less than 3.75 per gallon
I owned a Jetta 1.8T and when it was gone I lost all interest in ever buying premium fuel again.
I owned a Jetta 1.8T and when it was gone I lost all interest in ever buying premium fuel again.
#23
08-13-2008 | 06:17 PM
You seem to be confused, so let me see if I can help.
About gasoline, octane rating measures one thing and one thing only: resistance to detonation (knock, or compression ignition). Higher octane fuel does not explode more powerfully, it contains the same amount of energy as regular gas. It is possible to have a high octane fuel that contains less energy than a lower octane fuel (diesel vs. gasoline is a good example of this).
About ignition timing, advance refers to the number of degrees before top-dead center that ignition occurs. More advance is required for lower octane fuels as obviously the closer to TDC the greater the compression and the greater the chance of detonation. Conversely, higher octanes can run with less advance, as they can come closer to TDC without detonating.
About ECUs and ignition timing: Detonation is bad for an engine. If you've ever looked at the pistons and heads of an engine that's been knocking, you'll see tiny balls of metal stuck to them that were blown off the combustion chamber during detonation. To think that the engine in any modern car is constantly reducing advance until it hears detonation is laughable and a recipe for an unreliable engine (not something that Honda is known for).
That's not to say that knock sensors don't exist or that the ECU doesn't adjust ignition timing, it just works the opposite of what you seem to think. A modern car has a default ignition map designed for its recommended fuel. When the knock sensor detects detonation, ignition advance is increased until it goes away. This allows a car designed for premium to run regular when no premium is available (the original purpose behind the system). It has the added benefit of keeping a car from knocking if the compression ratio changes (say, from carbon deposits building up in the combustion chambers).
Finally, you can't tell from a compression ratio alone whether an engine would benefit from higher octane fuel. Displacement, combustion chamber shape, number of spark plugs per cylinder and bore:stroke ratio have almost as much effect on detonation as compression ratio. But the real trump card is whether the ECU is programmed by default to take advantage of the higher octane; in the case of the Fit it is not, or significant MPG gains could be realized just by switching to premium.
About gasoline, octane rating measures one thing and one thing only: resistance to detonation (knock, or compression ignition). Higher octane fuel does not explode more powerfully, it contains the same amount of energy as regular gas. It is possible to have a high octane fuel that contains less energy than a lower octane fuel (diesel vs. gasoline is a good example of this).
About ignition timing, advance refers to the number of degrees before top-dead center that ignition occurs. More advance is required for lower octane fuels as obviously the closer to TDC the greater the compression and the greater the chance of detonation. Conversely, higher octanes can run with less advance, as they can come closer to TDC without detonating.
About ECUs and ignition timing: Detonation is bad for an engine. If you've ever looked at the pistons and heads of an engine that's been knocking, you'll see tiny balls of metal stuck to them that were blown off the combustion chamber during detonation. To think that the engine in any modern car is constantly reducing advance until it hears detonation is laughable and a recipe for an unreliable engine (not something that Honda is known for).
That's not to say that knock sensors don't exist or that the ECU doesn't adjust ignition timing, it just works the opposite of what you seem to think. A modern car has a default ignition map designed for its recommended fuel. When the knock sensor detects detonation, ignition advance is increased until it goes away. This allows a car designed for premium to run regular when no premium is available (the original purpose behind the system). It has the added benefit of keeping a car from knocking if the compression ratio changes (say, from carbon deposits building up in the combustion chambers).
Finally, you can't tell from a compression ratio alone whether an engine would benefit from higher octane fuel. Displacement, combustion chamber shape, number of spark plugs per cylinder and bore:stroke ratio have almost as much effect on detonation as compression ratio. But the real trump card is whether the ECU is programmed by default to take advantage of the higher octane; in the case of the Fit it is not, or significant MPG gains could be realized just by switching to premium.
let me make a few corrections/ misunderstandings maybe you read me wrong
1.yes ignition happens before tdc. 0 degrees ignition advance means the spark is firing when the piston is at tdc, 20 degrees advance means the spark is firing 20degrees BEFORE the piston gets to tdc. to make power you need to increase ignition advance the higher you go on octane the higher you need to increase ignition advance. proof for this 110 octane on a k series requires about 34-37 degrees advance at wot.
93 octane on a k series is happy with 25-28 degrees advance at wot
87 octane doesnt like more than 23 degrees advance at wot. i've proven this on the dyno
with the ignition cleared out lets go to knocking. yes knocking is bad for the engine i agree with you. so does honda engineers but according to them one knock once in a while is ok therefore they have made ECUS to retard ignition once the knock sensor detects a knock. on honda engines the knock sensor is VERY sensible and 80% of the time it reads engine noise as a knock. honda made it that way. other manufacturers are following the trend as well.
as fas as engine compression goes heres the thing: higher compression allows for higher octane when properly tuned. low compression wont benefit that much from a higher octane. dont believe me? go to a nopi/nhra talk to the clutch masters guys or about anyone ask them what gas they are running and whats the compression of the engine.
i agree with you that it goes hand on hand with the map on the ECU. heres a past experience i had: a n/a k20a3 wont make any more power from changing from 87 to 93 octane due to its low compresion on a k20a type R engine you will loose power by switching to anything lower than 93 no matter if you tune to compensate for the loss. why because of the k20a's high compression.
so going back to the fit engine. again while the gains are very marginal and not something you would feel (other than a placebo effect) or unless you are testing on the dyno the relatively high compresion of the engine will allow for a small gain in power and in fuel economy.
i had a huge thread/ writeup on tunning a car for fuel economy on ephatch but it got deleted when the site crashed earlier this year. the conclusion of the thread was that higher octane when properly tuned led to better fuel economy due to the advance in ignition. BUT it was from about 3 more mpg. what made more fuel econ was leaning the mixture as much as possible while retarding ignition on 87 octane. i was able to do 32mpg on the city with no knocks recorded on datalogs.
again you dont have to believe me i say what i've proven myself not what i think it is.
on hondas ecu's and tunning read the tech articles over at hondata. they will give you an idea of how the engine works, how the honda ecu's work and therfore how it should be tuned.
read this articles they are long but its from the series of seminars hondata did back in 06 i attended the one in miami.
Tech - K-Pro training
Hondata Seminar
#24
08-13-2008 | 06:29 PM
Probably all just the placebo effect.
Actually you do, Europe uses a different scale... Same physical properties different units of measurement.
If we all listened to wrussi, then theoretically putting ethanol in your car would result in a huge increase in power and FE (because ethanol has a much higher octane).. which is definitely not the case... With out proper tuning and usually the use of a turbo charger, your HP will drop. Thanks red iron crown for correcting the mess..
Actually you do, Europe uses a different scale... Same physical properties different units of measurement.
If we all listened to wrussi, then theoretically putting ethanol in your car would result in a huge increase in power and FE (because ethanol has a much higher octane).. which is definitely not the case... With out proper tuning and usually the use of a turbo charger, your HP will drop. Thanks red iron crown for correcting the mess..
Last edited by wrussi; 08-13-2008 at 06:31 PM.
#25
08-13-2008 | 06:54 PM
Member
Joined: Feb 2007
Posts: 143
From: Corona, CA
Everything people say on forums is generally based on their own knowledge, which is fine. However if you call Honda of North America they will tell you that the ECU CAN take advantage of the higher octane gas and they actually strongly recommend it. If you don't believe me call their customer service. Remember something else, our engines have technically a higher compression ratio than the C32 in the NSX! 10.4:1 
I've been using 91 since I got my Fit even in the times when it was almost 5 a gallon, who cares? It's give or take 100 bucks a year difference honestly.
I've been using 91 since I got my Fit even in the times when it was almost 5 a gallon, who cares? It's give or take 100 bucks a year difference honestly.
#27
08-13-2008 | 07:02 PM
i have used regular gas for over a year on my fit. but my friend and also the mechanic for my fit, has told me that regular gas causes carbon build up, and premium burns cleaner and years down the road the car will appreciate that you have been putting premium in it. he recommended filling up with premium, or at least midgrade and then premium once a month. im just wondering if anybody can explain why this would be a waste if i chose to do this, if its pointless. i do plan on keeping my fit for a long time, just curious as to peoples ideas and if he is wrong...?
#28
08-13-2008 | 07:08 PM
Member
Joined: May 2008
Posts: 170
From: McDonough, GA
Nobody is arguing your experience with any particular engine here, just your explanation of it all.
First of all, there is no "explosion" taking place under normal operation of an internal combustion engine. It is a controlled burn process that is miles away from qualifying as an explosion. But I digress as it may just be a case of a poor choice of words.
Secondly, we have this statement here;
With your statement of needing more pressure to get the 100 octane to explode,you seem to be talking about a diesel engine here. I know you know this, and maybe you just didn't write what you meant to say, but you don't want the pressure to trigger the ignition process in a gasoline engine as you do with a diesel. Furthermore, high octane gas is not less flammable than low octane gas, it is simply more resistant to autoignition.
I also have a question about your timing example. If you tested the exact same engine with three different octane rated gasolines, it stands to reason that the higher octane gas could withstand more compression (read as less ignition advance) before autoignition than the lower octane gasoline would, yet you stated that the higher octane gas required more ignition advance. Could you explain this? Are you comparing apples to oranges here or what?
Again, no disrespect intended towards you or your experience with engines. It just seemed that the way you described things was going to confuse some people who don't know how this stuff works.
First of all, there is no "explosion" taking place under normal operation of an internal combustion engine. It is a controlled burn process that is miles away from qualifying as an explosion. But I digress as it may just be a case of a poor choice of words.
Secondly, we have this statement here;
I also have a question about your timing example. If you tested the exact same engine with three different octane rated gasolines, it stands to reason that the higher octane gas could withstand more compression (read as less ignition advance) before autoignition than the lower octane gasoline would, yet you stated that the higher octane gas required more ignition advance. Could you explain this? Are you comparing apples to oranges here or what?
Again, no disrespect intended towards you or your experience with engines. It just seemed that the way you described things was going to confuse some people who don't know how this stuff works.
#30
08-13-2008 | 11:38 PM
Member
Joined: Jun 2008
Posts: 54
From: NL, Canada
ok not to argue or anything but for the past 3 years i've been tuning k series and b series i've tuned a lot of cars. currently i've tuned one of south florida's fastest eg's with a k20a2 making 240whp 163tq i've gone to hondata seminars and read quite a lot about ecu operation and tunning last year i went to a AEM ems seminar so i would think i kinda have an idea of what im talking about. im not asking you to believe me. do your own research and you will find the truth.
let me make a few corrections/ misunderstandings maybe you read me wrong
1.yes ignition happens before tdc. 0 degrees ignition advance means the spark is firing when the piston is at tdc, 20 degrees advance means the spark is firing 20degrees BEFORE the piston gets to tdc. to make power you need to increase ignition advance the higher you go on octane the higher you need to increase ignition advance. proof for this 110 octane on a k series requires about 34-37 degrees advance at wot.
93 octane on a k series is happy with 25-28 degrees advance at wot
87 octane doesnt like more than 23 degrees advance at wot. i've proven this on the dyno
1.yes ignition happens before tdc. 0 degrees ignition advance means the spark is firing when the piston is at tdc, 20 degrees advance means the spark is firing 20degrees BEFORE the piston gets to tdc. to make power you need to increase ignition advance the higher you go on octane the higher you need to increase ignition advance. proof for this 110 octane on a k series requires about 34-37 degrees advance at wot.
93 octane on a k series is happy with 25-28 degrees advance at wot
87 octane doesnt like more than 23 degrees advance at wot. i've proven this on the dyno
with the ignition cleared out lets go to knocking. yes knocking is bad for the engine i agree with you. so does honda engineers but according to them one knock once in a while is ok therefore they have made ECUS to retard ignition once the knock sensor detects a knock. on honda engines the knock sensor is VERY sensible and 80% of the time it reads engine noise as a knock. honda made it that way. other manufacturers are following the trend as well.
In fact that's a good analogy. Waiting for knock to occur regularly to adjust the ignition timing is like using trees and telephone poles to stop your car. Sure, it's designed to do it, what with airbags and seatbelts and all, but it's not good for the car!
as fas as engine compression goes heres the thing: higher compression allows for higher octane when properly tuned. low compression wont benefit that much from a higher octane.
dont believe me? go to a nopi/nhra talk to the clutch masters guys or about anyone ask them what gas they are running and whats the compression of the engine.
i agree with you that it goes hand on hand with the map on the ECU. heres a past experience i had: a n/a k20a3 wont make any more power from changing from 87 to 93 octane due to its low compresion on a k20a type R engine you will loose power by switching to anything lower than 93 no matter if you tune to compensate for the loss. why because of the k20a's high compression.
i agree with you that it goes hand on hand with the map on the ECU. heres a past experience i had: a n/a k20a3 wont make any more power from changing from 87 to 93 octane due to its low compresion on a k20a type R engine you will loose power by switching to anything lower than 93 no matter if you tune to compensate for the loss. why because of the k20a's high compression.
so going back to the fit engine. again while the gains are very marginal and not something you would feel (other than a placebo effect) or unless you are testing on the dyno the relatively high compresion of the engine will allow for a small gain in power and in fuel economy.
So it's not like the Fit engine's balance of combustion chamber and compression ratio is appropriate for premium fuel just because it's compression ratio is the same as some larger engines running on premium. There's no secret performance waiting to be unlocked just by pumping higher octane gas.
again you dont have to believe me i say what i've proven myself not what i think it is.
Last edited by Red Iron Crown; 08-13-2008 at 11:49 PM.
#31
09-01-2008 | 01:40 AM
Member
Joined: Oct 2007
Posts: 2,304
From: Illinois
Ive been reading the posts about higher octane. I get over 40mpg is stop and go with some highway. I use BP ultimate only. Timing being advance is under acceleration is not because the fuel burns slower but because the engine is reving faster and the ecm is keeping up by advancing (Less time). There is a BIG difference is Gasolines other than octane. Premium in short is F1 racing fuel, burns clean,High denisity fuel for better mileage. They detune with a knock sensor and most of the correction is fuel trim come by pulling fuel which is better then adding fuel with the correction trim inside the ecm. You only need to get 5 percent better mileage to save money.
#32
09-01-2008 | 01:52 AM
you guys can argue about octane until you are blue in the face but the simple fact of the matter is that any pump gas in america has all sorts of conditioners and additives that are meant to make a cleaner burning fuel. good for the environment, bad for your engine. i put 104 unleaded in my car and it runs better than ever. mind you, i am boosted but when i drive out of boost, my car feels like it has much more power and runs smoother.
#33
09-01-2008 | 02:22 AM
Push My Button
Joined: May 2007
Posts: 4,997
From: Calgary, Alberta
Fit does not need premium gas, it also does not get any pep or additional power gains as described in the OP's post. Premium gas does nothing for your mileage and also nothing for longevity, it is not cleaner nor is it more pure in any way over regular.
As mentioned a few times, it is strictly for high compression. While the Fit may benefit from a mid-grade on extremely hot days sitting in rush hours traffic, it would still be fine on chugging away on regular as well. Now we all know the fit does have a pretty good compression rate, it is totally fine to use regular and you will not experience any kind of performance benefit to using a mid grade.
As a side note, higher octane fuel does technically have less energy than a lower grade fuel... so you may actually experience a tiny decrease in fuel mileage as a result.
Bottom line: Putting high grade fuel in your Fit is the equivalent of feeding your house plants 3$ bottled water when you have an adequate supply of tap water handy.
you guys can argue about octane until you are blue in the face but the simple fact of the matter is that any pump gas in america has all sorts of conditioners and additives that are meant to make a cleaner burning fuel. good for the environment, bad for your engine. i put 104 unleaded in my car and it runs better than ever. mind you, i am boosted but when i drive out of boost, my car feels like it has much more power and runs smoother.
Last edited by Sugarphreak; 09-01-2008 at 02:27 AM.
#34
09-01-2008 | 01:46 PM
I doubt u are really feeling any thing different in the car its more like the mind playing tricks. But read the manual it says regular. There is no need for premum fuel in the fit. But hey if u want to thats ur car do what u want to
#35
09-01-2008 | 01:48 PM
Bingo!
Fit does not need premium gas, it also does not get any pep or additional power gains as described in the OP's post. Premium gas does nothing for your mileage and also nothing for longevity, it is not cleaner nor is it more pure in any way over regular.
As mentioned a few times, it is strictly for high compression. While the Fit may benefit from a mid-grade on extremely hot days sitting in rush hours traffic, it would still be fine on chugging away on regular as well. Now we all know the fit does have a pretty good compression rate, it is totally fine to use regular and you will not experience any kind of performance benefit to using a mid grade.
As a side note, higher octane fuel does technically have less energy than a lower grade fuel... so you may actually experience a tiny decrease in fuel mileage as a result.
Bottom line: Putting high grade fuel in your Fit is the equivalent of feeding your house plants 3$ bottled water when you have an adequate supply of tap water handy.
Boosted is a whole different story, you can also tune your car to run on different grades.
Fit does not need premium gas, it also does not get any pep or additional power gains as described in the OP's post. Premium gas does nothing for your mileage and also nothing for longevity, it is not cleaner nor is it more pure in any way over regular.
As mentioned a few times, it is strictly for high compression. While the Fit may benefit from a mid-grade on extremely hot days sitting in rush hours traffic, it would still be fine on chugging away on regular as well. Now we all know the fit does have a pretty good compression rate, it is totally fine to use regular and you will not experience any kind of performance benefit to using a mid grade.
As a side note, higher octane fuel does technically have less energy than a lower grade fuel... so you may actually experience a tiny decrease in fuel mileage as a result.
Bottom line: Putting high grade fuel in your Fit is the equivalent of feeding your house plants 3$ bottled water when you have an adequate supply of tap water handy.
Boosted is a whole different story, you can also tune your car to run on different grades.
U got it right on the dot. This should be the end of the thread.
#36
09-01-2008 | 04:16 PM
Member
Joined: May 2008
Posts: 354
From: Saskatchewan
the debate of high octane vs low octane has been beaten to death but let me clarify what honda k series R series and L series do to deal with gas octane.
before we get to the car lets talk about the gasoline first
the octane number that you see is how hard the gasoline explodes a 100 octane will have a much more stronger explosion than 87. but it doesnt end there! it has a trade off, higher octane gas is not as flamable as a low octane meaning you need more time and pressure to get 100 to explode than what you need for 87.
with that clear lets move to the car. we all know that to make power you need a strong explosion in the cylinder but in order for you to benefit of lets say 100 octane you need to make sure that the engine can make the gas explode in the exact moment. so higher cylinder compression and ignition advance are needed/used.
please note that:
compression cannot be changed on the fly its set by the manufacturer or unless you change pistons, rings, gaskets
ignition can be changed on the fly IF the ECU allows it
on cars like the D series B series and ap1/2 F series ignition is set by honda and it does not move. thats why on a d series engine it doesnt benefit from putting 93 octane but on an s2k you will knock a lot if you dont put premium. these cars ECU's are preset for certain amount of ignition therefore requiring an specific octane rating.
this was kinda annoying for honda because for every country a car was sold in they had to create different ECU calibrations. due to the difference on octane from country to country
moving to the modern k series the R series and L series they made the ECU's for these cars that can change ignition on the fly. how it works is that the ECU its always advancing ignition +1 degree until it hears a knock. when it does hear a knock, ignition is retarded by 5 degrees. then the process is started all over again. this allows honda to use 1 map for all countries and at the same time optimizing performance regardless what octane is used.
the L series has a 10.4:1 compression therefore it will benefit from a little better octane rating in the gas because the ecu will advance ignition until it knocks
this should translate in about 3 more hp, nothing that you could feel that much. fuel econ should be up by a few mpg also.
so in conclusion is it worth it to put higher octane on the car? imo not really unless the price difference was under 5 cents between regular and premium i dont think its worth it to spend the extra 25/gal just to get 3 more hp and 1mpg...
before we get to the car lets talk about the gasoline first
the octane number that you see is how hard the gasoline explodes a 100 octane will have a much more stronger explosion than 87. but it doesnt end there! it has a trade off, higher octane gas is not as flamable as a low octane meaning you need more time and pressure to get 100 to explode than what you need for 87.
with that clear lets move to the car. we all know that to make power you need a strong explosion in the cylinder but in order for you to benefit of lets say 100 octane you need to make sure that the engine can make the gas explode in the exact moment. so higher cylinder compression and ignition advance are needed/used.
please note that:
compression cannot be changed on the fly its set by the manufacturer or unless you change pistons, rings, gaskets
ignition can be changed on the fly IF the ECU allows it
on cars like the D series B series and ap1/2 F series ignition is set by honda and it does not move. thats why on a d series engine it doesnt benefit from putting 93 octane but on an s2k you will knock a lot if you dont put premium. these cars ECU's are preset for certain amount of ignition therefore requiring an specific octane rating.
this was kinda annoying for honda because for every country a car was sold in they had to create different ECU calibrations. due to the difference on octane from country to country
moving to the modern k series the R series and L series they made the ECU's for these cars that can change ignition on the fly. how it works is that the ECU its always advancing ignition +1 degree until it hears a knock. when it does hear a knock, ignition is retarded by 5 degrees. then the process is started all over again. this allows honda to use 1 map for all countries and at the same time optimizing performance regardless what octane is used.
the L series has a 10.4:1 compression therefore it will benefit from a little better octane rating in the gas because the ecu will advance ignition until it knocks
this should translate in about 3 more hp, nothing that you could feel that much. fuel econ should be up by a few mpg also.
so in conclusion is it worth it to put higher octane on the car? imo not really unless the price difference was under 5 cents between regular and premium i dont think its worth it to spend the extra 25/gal just to get 3 more hp and 1mpg...
I copied this for you from another site.
It might seem odd that fuels with higher octane ratings burn less easily, yet are popularly thought of as more powerful. Using a fuel with a higher octane lets an engine be run at a higher compression ratio without having problems with knock. Compression is directly related to power, so engines that require higher octane usually deliver more power. Some high-performance engines are designed to operate with a compression ratio associated with high octane numbers, and thus demand high-octane gasoline. It should be noted that the power output of an engine also depends on the energy content of its fuel, which bears no simple relationship to the octane rating. Some people believe that adding a higher octane fuel to their engine will increase its performance or lessen its fuel consumption; this is false - engines perform best when using fuel with the octane rating they were designed for.
Premium fuel will not produce a more powerful "explosion" as you call it.
In fact it burns more slowly and has less tenddency to have multiple flashpoints.
#37
10-10-2008 | 02:14 AM
Member
Joined: Sep 2008
Posts: 622
From: Québec city
You seem to be confused, so let me see if I can help.
About gasoline, octane rating measures one thing and one thing only: resistance to detonation (knock, or compression ignition). Higher octane fuel does not explode more powerfully, it contains the same amount of energy as regular gas. -> Right!!
It is possible to have a high octane fuel that contains less energy than a lower octane fuel (diesel vs. gasoline is a good example of this). -> Wrong, Diesel have more energy then gas and more resistance to knock... regulars pump fuels wouldn't run at 20+:1 CR + turbo!! Also Diesel don't have Octane but Cetane numbers...
About ignition timing, advance refers to the number of degrees before top-dead center that ignition occurs. -> Right!
More advance is required for lower octane fuels as obviously the closer to TDC the greater the compression and the greater the chance of detonation. -> Wrong! Old cast iron engines had base timing fixed ATDC sometimes to acomodate regular fuels and because ignition controllers weren't powerful, didn't had knock sensors and also because Cast Iron heads retained so much heat that is would have pinked to death if they would had given more advance... try to push something that is moving toward you and you will see more pressure then if you push the exact same thing that is moving at the same speed but in the opposite direction...
Conversely, higher octanes can run with less advance, as they can come closer to TDC without detonating. -> Wrong too... Ignition ''Advance'' is the point where the spark plugs fires ''in advance'' of TDC... simplier said, the more advance you have, the sooner the plugs fires BTDC...
About ECUs and ignition timing: Detonation is bad for an engine. If you've ever looked at the pistons and heads of an engine that's been knocking, you'll see tiny balls of metal stuck to them that were blown off the combustion chamber during detonation. To think that the engine in any modern car is constantly reducing advance until it hears detonation is laughable and a recipe for an unreliable engine (not something that Honda is known for). -> Right and Wrong... Neon SRT-4 engines (I know them!) constantly adjust timing based on the Sensors inputs and fuel grade used... they advance and when they see a slight ping (not a severe ping that destroys an engine!) they retard a little... they get a range of correction based on RPM (plugs are firing more in ''advance'' at high rpm!)
That's not to say that knock sensors don't exist or that the ECU doesn't adjust ignition timing, it just works the opposite of what you seem to think. -> ....
A modern car has a default ignition map designed for its recommended fuel. When the knock sensor detects detonation, ignition advance is increased until it goes away. -> Wrong! Actually retard and not advance!
This allows a car designed for premium to run regular when no premium is available (the original purpose behind the system). It has the added benefit of keeping a car from knocking if the compression ratio changes (say, from carbon deposits building up in the combustion chambers). -> Maybe! But they also can program the ECM to add or remove timing ''on the fly'' based on the grade of fuel used... Hence the '' Only 87 Octane OR Higher'' in your instructions booklet... Don't go under 87 or it will ping (As stated in the booklet!) but feel free to use premium if you wish as the ECU has a certain range of adjustement... I even wonder if Hondas ECU are not calibrated for Premium and then allowed to run on regular through the knock Sensor... it would make a sense of ''87 Octane OR Higher''... Let's use data aquired from my 97 DOHC neon some time ago as an example. When we datalogged the Ignition advance with Regular and Premium, we saw an increase of more or less 6° at 5000Rpm and something like 10° at 7000rpm... The difference in power was noticeable too!!
Finally, you can't tell from a compression ratio alone whether an engine would benefit from higher octane fuel. Displacement, combustion chamber shape, number of spark plugs per cylinder and bore:stroke ratio have almost as much effect on detonation as compression ratio. -> Right!
But the real trump card is whether the ECU is programmed by default to take advantage of the higher octane; in the case of the Fit it is not, or significant MPG gains could be realized just by switching to premium. -> I personally saw repeted improvement in using premium... just not so much in the Fit's case and a lot in the neons... especially the modded ones!!
About gasoline, octane rating measures one thing and one thing only: resistance to detonation (knock, or compression ignition). Higher octane fuel does not explode more powerfully, it contains the same amount of energy as regular gas. -> Right!!
It is possible to have a high octane fuel that contains less energy than a lower octane fuel (diesel vs. gasoline is a good example of this). -> Wrong, Diesel have more energy then gas and more resistance to knock... regulars pump fuels wouldn't run at 20+:1 CR + turbo!! Also Diesel don't have Octane but Cetane numbers...
About ignition timing, advance refers to the number of degrees before top-dead center that ignition occurs. -> Right!
More advance is required for lower octane fuels as obviously the closer to TDC the greater the compression and the greater the chance of detonation. -> Wrong! Old cast iron engines had base timing fixed ATDC sometimes to acomodate regular fuels and because ignition controllers weren't powerful, didn't had knock sensors and also because Cast Iron heads retained so much heat that is would have pinked to death if they would had given more advance... try to push something that is moving toward you and you will see more pressure then if you push the exact same thing that is moving at the same speed but in the opposite direction...
Conversely, higher octanes can run with less advance, as they can come closer to TDC without detonating. -> Wrong too... Ignition ''Advance'' is the point where the spark plugs fires ''in advance'' of TDC... simplier said, the more advance you have, the sooner the plugs fires BTDC...
About ECUs and ignition timing: Detonation is bad for an engine. If you've ever looked at the pistons and heads of an engine that's been knocking, you'll see tiny balls of metal stuck to them that were blown off the combustion chamber during detonation. To think that the engine in any modern car is constantly reducing advance until it hears detonation is laughable and a recipe for an unreliable engine (not something that Honda is known for). -> Right and Wrong... Neon SRT-4 engines (I know them!) constantly adjust timing based on the Sensors inputs and fuel grade used... they advance and when they see a slight ping (not a severe ping that destroys an engine!) they retard a little... they get a range of correction based on RPM (plugs are firing more in ''advance'' at high rpm!)
That's not to say that knock sensors don't exist or that the ECU doesn't adjust ignition timing, it just works the opposite of what you seem to think. -> ....
A modern car has a default ignition map designed for its recommended fuel. When the knock sensor detects detonation, ignition advance is increased until it goes away. -> Wrong! Actually retard and not advance!
This allows a car designed for premium to run regular when no premium is available (the original purpose behind the system). It has the added benefit of keeping a car from knocking if the compression ratio changes (say, from carbon deposits building up in the combustion chambers). -> Maybe! But they also can program the ECM to add or remove timing ''on the fly'' based on the grade of fuel used... Hence the '' Only 87 Octane OR Higher'' in your instructions booklet... Don't go under 87 or it will ping (As stated in the booklet!) but feel free to use premium if you wish as the ECU has a certain range of adjustement... I even wonder if Hondas ECU are not calibrated for Premium and then allowed to run on regular through the knock Sensor... it would make a sense of ''87 Octane OR Higher''... Let's use data aquired from my 97 DOHC neon some time ago as an example. When we datalogged the Ignition advance with Regular and Premium, we saw an increase of more or less 6° at 5000Rpm and something like 10° at 7000rpm... The difference in power was noticeable too!!
Finally, you can't tell from a compression ratio alone whether an engine would benefit from higher octane fuel. Displacement, combustion chamber shape, number of spark plugs per cylinder and bore:stroke ratio have almost as much effect on detonation as compression ratio. -> Right!
But the real trump card is whether the ECU is programmed by default to take advantage of the higher octane; in the case of the Fit it is not, or significant MPG gains could be realized just by switching to premium. -> I personally saw repeted improvement in using premium... just not so much in the Fit's case and a lot in the neons... especially the modded ones!!
Last edited by DOHCtor; 10-10-2008 at 03:03 AM.
#38
10-10-2008 | 02:32 AM
Member
Joined: Sep 2008
Posts: 622
From: Québec city
Probably all just the placebo effect.
If we all listened to wrussi, then theoretically putting ethanol in your car would result in a huge increase in power and FE (because ethanol has a much higher octane).. which is definitely not the case... With out proper tuning and usually the use of a turbo charger, your HP will drop. Thanks red iron crown for correcting the mess..
If we all listened to wrussi, then theoretically putting ethanol in your car would result in a huge increase in power and FE (because ethanol has a much higher octane).. which is definitely not the case... With out proper tuning and usually the use of a turbo charger, your HP will drop. Thanks red iron crown for correcting the mess..
-The higher octane allows more boost and\or timing advance...
-The rich mixture has a cooling effect a little like water injection that cools the air charge...
That's why certain dudes in the quest on max power use E85 as their fuels of choice...
Marko!!
#39
10-10-2008 | 02:42 AM
Member
Joined: Sep 2008
Posts: 622
From: Québec city
If you tested the exact same engine with three different octane rated gasolines, it stands to reason that the higher octane gas could withstand more compression (read as less ignition advance) before autoignition than the lower octane gasoline would, yet you stated that the higher octane gas required more ignition advance. Could you explain this? Are you comparing apples to oranges here or what?
Marko!!
#40
10-10-2008 | 08:32 AM
Member
Joined: Feb 2007
Posts: 689
From: Alabanana
So here's a slightly different question.
First, let me say this:
In my older cars, I have always noticed a big difference when running gas from a "name brand" company versus the cheap gas from Raceway or Walmart (Murphy).
My previous cars seemed to get better power and MPG from BP or Chevron gasolines. Consequently, I have always run BP/Amoco or Chevron/Texaco gas in my Fit. With the recent gasoline availability and price problems due to hurricanes Gustav and Ike, I ran a couple of tanks from Raceway and one from Costco, and it seemed to me that, just like the cars before it, the Fit didn't run as well or efficiently.
So my question is, what is the difference? Thanks for whatever you guys can tell me.
First, let me say this:
In my older cars, I have always noticed a big difference when running gas from a "name brand" company versus the cheap gas from Raceway or Walmart (Murphy).
My previous cars seemed to get better power and MPG from BP or Chevron gasolines. Consequently, I have always run BP/Amoco or Chevron/Texaco gas in my Fit. With the recent gasoline availability and price problems due to hurricanes Gustav and Ike, I ran a couple of tanks from Raceway and one from Costco, and it seemed to me that, just like the cars before it, the Fit didn't run as well or efficiently.
So my question is, what is the difference? Thanks for whatever you guys can tell me.
Last edited by Steeldog; 10-10-2008 at 08:34 AM. Reason: Clarification