Just for a lark, I went back to my old gas fillup books to compare the car's current mileage with what it achieved earlier in its life. The car now has 223,000 miles on it and gets about 2,500 miles to the quart of oil. It recently passed emissions with very low numbers except for high NOx, that due to an old cat. For HC and CO, this car can pass Ontario's 2001 emissions standards. It's interesting to see that the car's gas mileage appears to have degraded not at all in 13 years and 223,000 miles of driving. As an aside, I also noticed that the use of Premium gas (91 pump octane) results in a predictable 2% drop in gas mileage. Apr24-Jul28, 1991: Mostly city driving 5.7 miles on odometer. Car was NEW. 169.27 USgal 3552.97 miles ****20.99 mpg Jan12-Apr12, 1992: Mostly city 15,000 on odometer 143.18 USgal 3604.7 miles ****25.18 mpg Feb1-Apr7, 1994 Mostly city 57,000 on odometer 131 USgal 3265.2 miles ****24.93 mpg (stopped keeping track for a few years) Feb8-Apr19, 2001 Mostly highway 170,000 on odometer 126.77 USgal 3593.86 miles ****28.3 mpg June10-July24, 2003 Mostly highway 210,000 on odometer 67.96 USgal 2011.3 miles ****29.59 mpg Dec5-Feb6, 2004 Mostly highway (VERY cold weather) 220,000 on odometer 88.39 USgal 2446.65 miles ****27.7 mpg Feb10-Apr1, 2004 Mostly highway 223,000 on odometer 81.78 gal 2330.83 miles ****28.5 mpg -- TeGGeR® The Unofficial Honda FAQ http://www3.telus.net/public/johnings/faq.html How to find anything on the Internet or in Usenet Groups: www.google.com www.groups.google.com
My 98 Civic Hatch gets about 4% drop in gas mileage when using the Premium gas vs the Regular stuff. I'm averaging about 6.7L/100KM of combined driving on Regular gas. The car has 165,000KM and burns about .5L of oil every 5000KM. Pars
||> As an aside, I also noticed that the use of Premium gas (91 pump octane) ||> results in a predictable 2% drop in gas mileage. || ||My 98 Civic Hatch gets about 4% drop in gas mileage when using the Premium gas ||vs the Regular stuff. I'm averaging about 6.7L/100KM of combined driving on ||Regular gas. The car has 165,000KM and burns about .5L of oil every 5000KM. Higher octane gas takes away from the power-producing potential of the fuel. The octane additives take away from the actual fuel volume. Most cars will get slightly less economy and/or produce slightly less power using premium fuel. The excepts are those cars who fuel/timing curves are optimized for a higer octane. That is, the timing must be so retarded to accomodate the low octane that efficiency suffers, If the engine is designed for low octane, that won't be the case. We have found that our NB Turbo gets best economy on premium, the 300M on mid-grade (87 or 91 octane). My Spec RX7 race car develos the most HP on the lowest octane gas I can find, usually 87. Rex in Fort Worth
I'm not sure there's anyplace left where octane additives are still in use, certainly not in the U.S. apart from the ethanol, which has its own loss of combustion energy vs. hydrocarbons. Modern gasoline gets its octane from refining techniques, like hydrocracking, alkylation, isomerisation and the traditional reforming. The reason you get slightly better mileage with a lower octane gas is because the molecules of the higher octane components have a lower thermal energy per unit mass, e.g. BTU/lb when combusted than the lower octane components. It's more to do with compression ratio of the engine design, though that does impact on fuel and ignition parameters. With a higher octane gas, you need the higher compression to get the higher energy output; without it you get no benefit and a small penalty. Rgds, George Macdonald "Just because they're paranoid doesn't mean you're not psychotic" - Who, me??
