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Thread ID: 70673	2006-07-12 06:04:00	OT - Does US have different octane rating compared to us?	SKT174 (1319)	PC World Chat

Post ID	Timestamp	Content	User
470275	2006-07-12 06:04:00	I've been visiting various US car forums and noticed that most of them are using either 87 / 89 / 91 / 93 octane fuel while we get 91 / 95 / 98 here ... :confused:	SKT174 (1319)
470276	2006-07-12 06:40:00	Yes and no :) www.madabout-kitcars.com	Terry Porritt (14)
470277	2006-07-12 15:35:00	It's an apples to oranges comparison, I think with other countries and even other states here in the US . At about 1972 or so, the old octane numbers were changed to R+M divided by 2, and that made a lot of people angry, as they had lived with "Octane" that was just . . . well . . . octane without new and much lower values or ratings . At the same time as the lower octane became available, engines had an EGR device attached to them to lower combustion chamber temperatures and lower the octane requirements of vehicles by diluting the charge of fuel and air in the combustion chamber with exhaust gasses that would just take up some of the room in the combustion chamber allowing for more economy during cruise and moderate speeds on freeways . EGR devices are a good thing . . . they really work and are not detrimental to the engine at all . One of the finest fuels that we usta have (1960-1966 I think) was Chevron White Pump, which was 108+ octane and would work for aircraft engines . It was expensive, ($0 . 249/gallon) . . . that's twenty four point nine cents a gallon! If you had an engine with 13:1 compression ratio, then this was the only fuel to run . We had fuels at the pumps that could run from 83 to 101 octane, and we even had one brand called "Hancock" that let you dial whatever octane you wanted from two mixes in the ground by different ratios and prices . In comparison, most engines today run about 8 . 25:1 ratios and require a lot less octane . Nowadays, here in California we see just three values for octane, 87/89/91 . To arrive at these numbers, gasoline pumps typically post octane numbers as an average of two different values . Often you may see the posted octane rating formula as (R+M)/2 . One value is the research octane number (RON), which is determined with a test engine running at a low speed of 600 rpm . The other value is the motor octane number (MON), which is determined with a test engine running at a higher speed of 900 rpm . We had been told the "M" stands for "Methode", which probably means the same thing, just a way of testing has some sort of French connection . . . just to make it mysterious and too hard to understand . If, for example, a gasoline has an RON of 98 and a MON of 90, then the posted octane number would be the average of the two values or 94, but we never see values this high . If we are talking common vehicles here in the US, they are mandated to be able to use 87 octane fuel, but there are a few exceptions . . . like the Volvo, which has always required premium octane fuel for some dumb reason .	SurferJoe46 (51)
470278	2006-07-12 22:53:00	Thanks for the detailed explanation guys. I found that roughly add about 5 points in the US to make it similar to NZ octane rating, I know it's not exact but it's close enough :D	SKT174 (1319)
470279	2006-07-12 23:37:00	It's an apples to oranges comparison, I think with other countries and even other states here in the US . At about 1972 or so, the old octane numbers were changed to R+M divided by 2, and that made a lot of people angry, as they had lived with "Octane" that was just . . . well . . . octane without new and much lower values or ratings . At the same time as the lower octane became available, engines had an EGR device attached to them to lower combustion chamber temperatures and lower the octane requirements of vehicles by diluting the charge of fuel and air in the combustion chamber with exhaust gasses that would just take up some of the room in the combustion chamber allowing for more economy during cruise and moderate speeds on freeways . EGR devices are a good thing . . . they really work and are not detrimental to the engine at all . One of the finest fuels that we usta have (1960-1966 I think) was Chevron White Pump, which was 108+ octane and would work for aircraft engines . It was expensive, ($0 . 249/gallon) . . . that's twenty four point nine cents a gallon! If you had an engine with 13:1 compression ratio, then this was the only fuel to run . We had fuels at the pumps that could run from 83 to 101 octane, and we even had one brand called "Hancock" that let you dial whatever octane you wanted from two mixes in the ground by different ratios and prices . In comparison, most engines today run about 8 . 25:1 ratios and require a lot less octane . Nowadays, here in California we see just three values for octane, 87/89/91 . To arrive at these numbers, gasoline pumps typically post octane numbers as an average of two different values . Often you may see the posted octane rating formula as (R+M)/2 . One value is the research octane number (RON), which is determined with a test engine running at a low speed of 600 rpm . The other value is the motor octane number (MON), which is determined with a test engine running at a higher speed of 900 rpm . We had been told the "M" stands for "Methode", which probably means the same thing, just a way of testing has some sort of French connection . . . just to make it mysterious and too hard to understand . If, for example, a gasoline has an RON of 98 and a MON of 90, then the posted octane number would be the average of the two values or 94, but we never see values this high . If we are talking common vehicles here in the US, they are mandated to be able to use 87 octane fuel, but there are a few exceptions . . . like the Volvo, which has always required premium octane fuel for some dumb reason . In the interests of tapping a reliable source of info on such matters, how about an explanation of the impact of using a higher octane than necessary?	Lizard (2409)
470280	2006-07-13 00:48:00	When all of the smoke and mirors are gone, the effects of using a higher octane fuel in an engine gets really simple to comprehend . Octane, for all it's worth is really just a fuel flame inhibitor . It slows down combustion to make it less likely that the fuel will self-ignite due to just the thermal effects of compresson . If one were to take one liter of air, and compress it to a much smaller size . . say about 1/10th it's normal volume, that would be a 10:1 compression ratio in essense . The same thing if you take it to 1/2 it's normal volume . . that's a 2:1 ratio . Now . . . there's heat generated in compressing air or any gas for that matter . The higher the compression of the captive gas, heat is produced in the same proportion, although not in a linear scale . Additionally, the higher pressures in an engine with high compression generate higher temperatures than a lower compression engine and this is before the fuel is burned . In an engine running a decent value of 8 . 5:1 compression ratio, then most time 87 octane will suffice . If you use a higher octane fuel in that same engine, the fuel is still burning visciously as it then gets passed thru the exhaust valve and dumped into the tailpipe, out to the atmosphere . On a scale of wastefullness, this is very high . Heat is the product of the fuel and it is needed to be inside the engine to produce power; to have it wasted still burning going to the atmosphere will produce lowered economy and performance . Exhaust valve life is seriously cut short as it is not designed to handle a flow of a near-plasma gas . Catalytic convertors will die an early death in this superheated flow; exhaust systems have been known to glow brightly as the still-burning fuel goes thru the muffler and tailpipe . Exhaust manifolds crack and warp because of the same effect . Money is wasted by the engine because it needs MORE fuel to accomplish moving the mass of metal, rubber, plastic and carbon-based life forms (the driver) down the road in compensation to the lowered power produced . Higher octane does not produce more power or performance on engines that do not require it, it makes them run worse and for a shorter period of time .	SurferJoe46 (51)
470281	2006-07-13 01:02:00	In the interests of tapping a reliable source of info on such matters, how about an explanation of the impact of using a higher octane than necessary? I think using a lower octane than recommended would have a much higher degree of impact than using a higher octane than necessary. Especially for high performance car which leads to knocking and some other things which I'm not sure. :D The newer car can actually adjust to the lower octane but you use lower octane than the minimum requirement, you might loose performance and get crappy mpg which in the end would have costs more...	SKT174 (1319)
470282	2006-07-13 01:46:00	Running with a higher octane rating than that recommended for the compression ratio and ignition timing does not have any deleterious effects upon an engine at all. I just don't know where Joe gets such an idea from, especially as he is/has been in the trade. All it will do is make your pocket a bit lighter :) I dont know about "modern" engines with computer management/variable valve timing/variable ignition timing, they may well accomodate lower octane ratings without so much 'pinking', but it is running with too low an octane rating that will cause knocking and premature bearing failure. I have noticed a distinct tendency amongst New Zealand drivers to be reluctant to change down gear when low speed cornering around town, creating horrible 'pinking'.	Terry Porritt (14)
470283	2006-07-13 02:04:00	Almost all the books about the RAF in WW2 refer at some point to the way aircrew used aviation petrol (which was about 100 or so octane) in their cars. They didn't have petrol rationing. Modern fighter pilots have probably discovered that most cars don't run well on kerosine, so they don't get that perk.	Graham L (2)
470284	2006-07-13 02:57:00	Almost all the books about the RAF in WW2 refer at some point to the way aircrew used aviation petrol (which was about 100 or so octane) in their cars. They didn't have petrol rationing. Modern fighter pilots have probably discovered that most cars don't run well on kerosine, so they don't get that perk. Right, and their pre-war cars didn't blow up or burn out on the aviation spirit :), at that time the only petrol available for domestic use, that is, if one qualified for a petrol allowance was "Pool petrol", generally having an octane rating of between 72 to 75 or so. There used to be available grey coloured 'lozenges' to drop in the tank, that were supposed to increase the octane rating. Pool petrol continued well into the 1950s and that was all that was available when I started motorcycling. Premium grade which was about 85 octane arrived sometime around 1955 or so.	Terry Porritt (14)
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