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Sedans Honda Civic Honda Civic Real World MPG
2058 messages, Last post on Aug 26, 2009 at 6:19 PM
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Replying to: izmirian (Sep 15, 2008 5:29 pm) I think your mpg is very normal (more or less same as mine). You can experiment by using higher octane gas to see if there is any improvement.
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Replying to: wai (Sep 15, 2008 6:46 pm) Here are the conclusions, based on modern, computer controlled vehicles. There is no more energy in 92 than in 87. If a modern day car is designed to run on 87, there is no advantage to running 92. Higher octane simply means the fuel's ability to reduce the chances of engine "KNOCK" while under stress. Such as towing, heavy loads, red line operation, turbo or super charger applications, and such. Engine ignition "spark" is timed so that the fuel ignition begins when the piston has almost reached or slightly over ridden "TOP DEAD CENTER" of it's travel, and is ready for the "Explosion" that drives it down for it's power stroke. That explosion actually takes place over a period of time. The faster the piston is traveling, the earlier the spark can take place or "LEAD". If the chamber should over heat due to stressfull conditions, that extra heat can contribute to "pre-ignition", where the fuel is totally ignited too early. Under those stressfull conditions, if the engine should knock, the KNOCK SENSOR in the engine will retard the spark timing to compensate. Higher octane has additional additives to help prevent the knock and therefore help to keep the computer from having to retard the spark. Thereby probably helping to achieve slightly better mileage under those stressfull conditions. It gets a bit more complicated than that, but in layman terms that is the story. Bottom line. Under "Normal" conditions use the octane required by the manufacturer. There is no more energy in 92 than in 87. There are more "Anti-Knock" additives in the higher octane fuels. Under all "Normal" driving conditions, the engine computer will deal with the timing. One last thing. The temp gauge in the dash is reading water temperature. It will not indicate, except in rare conditions, the stress in the combustion chamber. So if you hear a "pinging" sound when the engine is under stressfull loads, a higher octane fuel may be in order, even though the temp gauge shows normal.  Kip
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Replying to: kipk (Sep 16, 2008 5:21 am)
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the increased power in higher octane fuels comes from the "slower burn" of the high octane fuel. This sounds opposite of common sense, but a slower/ more even burn will give more power than a quick flash burn of a low octane. Higher compression engines are more prone to compression-ignition, that is, the fuel burns due to pressure instead of spark, and since compression burn (similar to a diesel) almost always happens too soon, pinging is the result. The engine with knock sensors will detect this and retard or delay the spark to reduce the pinging. Unfortunately retarding the ignition also reduces the power. So by using low octane fuel that is prone to pinging, the engine with knock sensors retards and power is lost. That's how lower octane fuel lowers power. In engines without knock sensors, the burn is just faster and that faster burn reduces power. And the knocking severely impacts engine life. The loss of power is noticeable in some cars more than others. My 97 Camry v6 (3.0L, 10.5:1 compression) was very much affected by octane. 93 would make it scream. My wife's 02 Highlander (same engine but with VVTI) has much less noticeable power loss on 87 vs 93. The VVTI in Toyota's case combined with newer ECU controls seems to avoid much of the discernable power lost by using 87 (91 is recommended in both the 02 Highlander and the 97 Camry). Honda's controls work in basically the same way. |
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Replying to: wai (Sep 16, 2008 5:59 am) |
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Replying to: targettuning (Sep 16, 2008 6:47 am) Well stated and I agree !. Most of the research I did came from publications produced by various oil companies. Slower burn of high octane allows the ignition timing to be set earlier. This will not necessarily benefit an engine that has a "timing" designed for 87 octane. Except when the combustion chamber is being really stressed above and beyond normal, and running hotter than normal. In other words, using 93 won't necessarily trigger the timing to advance, so the slower burn can be utilized. That is my understanding and we normally get excellent mileage. I personally can't understand why folks buy an "Economy" car and want to find ways to spend as much money as possible on fuel. To each his own !  Kip |
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Replying to: targettuning (Sep 16, 2008 6:47 am) I've never seen gasoline lower than 87 octane, at least not labelled as gasoline.
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Replying to: izmirian (Sep 15, 2008 5:29 pm) Well I get that in my 2008 Civic Si which is a 6 spd manual and 197HP. I think your mileage will go up as you get more miles on the car. |
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Replying to: kenlw (Sep 18, 2008 9:58 am) |
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Suddenly, without any apparent reason, my MPG jumped dramatically from 26 mpg to 37 mpg. It's an 07 Civic EX, automatic, with 30,000 miles on it. I had been getting a low of 25 mpg to a high of 27-point-something for the life of the car, but then two tanks ago, it went up a little... to 29 mpg on one tank. Then, two days ago, I drove from So Cal to Fresno, about a 500 mile round trip. I got 37.5 mpg. I had the air conditioner going full blast, and my gas was the same... Costco 87 octane. Not only that, but I had to scale Angeles National Forest through I-5's Grapevine. This meant climbing with high RPM's for miles. I can't understand it. Since the beginning of this model year, there seems to have been two camps of owners. Those who get Civic-like mpg, and those like me who did not and who were surprised by lower mpg. Now my car has dramatically joined the first group. Has anybody else had an experience like this? Is there any rational explanation for it?
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