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ycr99

Grade Of Gas

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I haven't seen any documented test - scientific or otherwise. Only tests I;ve seen or heard about were from other posters. I've run my own tests - double blind test for me is to have my wife fill up and tell me what was used later.

 

What I've seen is that a properly tuned factory car will realize no performance difference between the octane (assuming that regular gas is truely 87 octane (85 in some places)). But if a car has a significant amount of miles and pings with regular gas (assuming everthing else is OK) - then running a higher octane fuel would be beneficial. Old school rules no longer apply to cars with variable timing and advance computer control - used to be car swith 9:1 C/R had to run premium - know you see cars running 10:1 or more running regular gas.

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my friend with a 2000 mitsubishi eclipse GS (4 cylinder, 87 octane) has a wonderful little device called a pocket logger which monitors ALL the obd2 data streams and can log them. he plotted load vs tps vs rpm vs vehicle speed vs AFR vs O2 voltage with tanks of 87, 89, and 93 octane fuels. on his engine (which has a knock sensor) there was NO change in timing with higher octane fuel, no change in AFR, no change in O2 voltage.

 

fish, if you'd like i could try and get the data from him, its such a neat device. its a program that runs on a palm pilot and has a cable that plugs into the OBD2 port. if he ever gets a tuning device (safc or emange) i could literally street tune his car with information ONLY from the pocketlogger, he wouldnt need to log any dyno time.

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That is pretty sweet - I use my CarChip to log data. Streamimg resolution is not very fast (once every 5 seconds) - I'm hoping I can play around with the SDK and write my own wrapper and possibly get better resolution (supposedly the ECM reports on the order of 10Hz or more).

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i beleive when sampling all the parameters he gets a cycle of one sample per variable every second. so the more variables you monitor the slower they refresh since the OBD2 ports bandwidth is limited, some cars are faster sample rates than others. the pocket logger is mitsu/chrysler specific unfourtunately, its a pretty cool. he's also got a laptop with an adapator and software which does the same as the pocket logger and then some.

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So if there is no significant improvement in gas mileage with a higher octane rating, then just buy the cheapest??

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So if there is no significant improvement in gas mileage with a higher octane rating, then just buy the cheapest??

Absolutely right - no need to buy higher octane than needed. As a caveat - the best octane to use could change with vehicle use and age. The correct octane to use is the one that doesn't cause the engine to "ping" during normal operation. Most modern fuel injected cars with decent computer control can help with running regular gas longer (by precisely controlling fuel, timing, and spark - they can reduce emissions, boost economy, and minimize deposits). Eventually - the computer will not be able to compensate for certain situations (towing for example) - that will cause the engine to ping or detonate on regular gas. You will not hurt anything by running higher octane in those situations. Same goes with car that require premium - you could run regular, but you are really playing with fire there. Run the octane that the car seems to like the best - drivability, economy, etc. and you should be golden.

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Fishexpo is exactly correct: "a properly tuned factory car will realize no performance difference between the octane (assuming that regular gas is truely 87 octane (85 in some places)). But if a car has a significant amount of miles and pings with regular gas (assuming everthing else is OK) - then running a higher octane fuel would be beneficial."

 

Octane and energy content of fuels are 2 separate issues. As long as an engine gets the octane it "needs", energy content determines MPG.

 

Early in my career, I worked at an oil company. They were somewhat mystified at the demand for premium unleaded (when we 1st switched to unleaded gas in 1975, only 87 octane was available) because most customers who bought premium didn't need it.

 

Even gasolines of the same octane can vary station-to-station and overtime at the same station. Gasoline is a complex mixture that is never the same. Also, when you fill up, you can't know whose gasoline you are actually buying. Most oil companies have exchange agreements in which they supply nearby gas stations in exchange for a competitor doing it elsewhere. In the US this further complicated by the fact that we are importing more and more gasoline. I follow Bikeman & buy what's ever cheapest.

 

For more, see "Don't buy a higher octane gasoline to improve fuel economy."

http://www.chevron.com/products/prodserv/f...n/fuel_economy/

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Good post and everyone will agree with, but with one correction.

I would rather say: "buy what's ever cheapest" major brand. No brand cheap gas can easily mean substandard, contaminated gas, or gas with too little additives. Remember, states test randomly for octanes and pump volume and nothing else. In my area, cheap gas from the no brand stations would produce a major sulfur stink.

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In the US, by law, all gasoline sold must contain the additives required by EPA. The level is small (if I remember correctly ~200 ppm). The additives are added at the terminal, not the station. The major oil companies are magnets for audits by EPA and others and it wouldn't make sense for them to "help" independents violate the law by not adding the additives.

 

Think about it from the perspective of a no-brand gas station: they don't have their own refineries. They generally buy gas from the major oil companies on the spot market. When gas supplies get tight (as it did in after Katrina or more recently because of the switch to ethanol), the price at independent stations is notably higher than at the majors (in NJ, Exxon was ~10-12 cents less than the independents when they are usually ~10 cents more). This is because of the spot market purchases.

 

A refinery doesn't refine a batch of gas for a single station. They continously refine huge amounts that is sent out to many many terminals. It's a fungible commodity. Hence, it is very unlikely that a single station would get a bad batch - odds are many many would be affected and I don't ever remember reading of this or hearing of it when I worked in oil.

 

(sidenote so there isn't confusion: Oxygenates aren't considered "additives")

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The gas station up the street has gone to $3.11 a gallon for 87 octane. If it continues to rise I will have to quit my job and go on welfare to afford to live.

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