I've just brought a 2004 Eclise GTS home, I drove 91 octane(prem) from LV to Calgary, AB, Canada because it was cheap compared to here ($45 to fill vs $65)

I know it says to run premium fuel, but why? And will it hurt to run 87 Octane?

If I can save a chunk of change every time I fill up, I can spend more on future mods! ;)

Thanks!

Yes it can hurt your engine. I don't know exactly how but I do know that if you use lower octane than recommended for your car it will cause it to run horribly. It'll feel bogged down and you won't feel like you're getting near the power you should be getting. and it will dirty up your cylinders alot faster if you don't use the recommended octane gas in your car.

The rule is it won't hurt your car to use a higher octane than recommended, but it will hurt it to use lower than recommended.

the 3.0L V6 GTS motor runs like garbage on 87 octane. you think you will be saving money to use cheaper gas, but you will have to fill up more often.

i believe the reason it calls for 91 octane, is due to the range in which your engine operates correctly without pre-detonation.. your knock sensor detects pre-detonation and if you use a improper octane rating your engine tends to pre-detonate, then causing the knock sensor to retard your timing. this causes fuel efficiency problems, and loss of power.

loss of HP does not mean less fuel consumption, even though a 92HP mirage will drive 35 miles per gallon on the freeway, a 13HP scooter will drive 80 miles a gallon. proof that less power does not mean better gas mileage: a 5HP mini drag car will make 3 quarter mile runs and need the 1/4 gallon tank to be filled up again. that equals to 3 miles per gallon.

if you do decide to use 87 octane, i suggest you also use a octane booster. the best type of octane booster for gasoline uses ETHERS, such as MTBE, TAME, and ETBE. unlike the alcohol octane boosters ether will not combine with water. so if you have any water in your gas tank you will not end up with a puddle of water sitting at the bottom of your tank, like when alcohol octane boosters are used. also ethers do not separate from gasoline, it blends just like a hydrocarbon. once its in, it spreads and blends.

octane boosters are better for obtaining higher octane levels with lower octane gasoline, than helping high octane gasoline reach higher performance.

if anyone chooses to look for performance enhancing abilities in fuel, either go for 100-105 racing octane gasoline, grab a nos kit, or make a ether injection system. direct ether injection will raise your octane as it is not diluted, and it has a direct octane rating of 110 and also has a molecular compound containing oxygen. so using it will not only bring your octane from 91 to 100.5 , but also add high levels of oxygen to your combustion cycle. it is optimum for top end RPM burning without the cost of using racing gasoline, that is if you plan on a more drag race approach than a track race.

i used to work on military trucks, and one day we were screwing around and decided to put the cold start ether injection system from the air box to the throttle body for fun. when we hit the cold start button, Hoooooly $hit!!!! especially since it was on a diesel with both a supercharger and turbo charger. BAM that fuker had the two engaged driving wheels spinning so quick is was scary. fun as hel L, but still scary. (when you have a 62 thousand pound truck with 20 inch rims and super aggressive tires that make the 20 inch rims look like baby rims spinning the tires you come to me and tell me its not scary fun)

ok now remember a higher octane rating uses more force when detonated. its like using a sledge hammer on your cylinder heads to drive your car. so be sure your connecting rods, your cylinder head, and your crank shaft can handle it before you go using it. don't go blaming me for you snapping a connecting rod and shoot it through your oil pan. i take no responsibility if you do.

Octane boosters are pointless. They don't do hardly anything for upping the octane rating of your gasoline(at least not nearly as much as they claim to) you'd be lucky to jump from 91 to 93 octane. Your best bet if you want a higher octane fuel is to get the gas from a race track if you plan on racing your car alot.

But if you're just looking to get the best fuel mileage for the least amount of money, just put the recommended octane gasoline in your car and drive it nicely. Simple as that.

see that is where you are not being specific enough.

fuel additives like octane boosters do have a diminishing effect on higher octane fuels. putting a set percentage in a tank of 91 octane will gain less octane than the same percentage in a fuel tank full of 87 or 85. using it in a lower octane fuel can more accurately help to reach towards the desired octane without the expense of higher octane fuel.

its really about your engine timing not the grade of fuel. higher fuel grades offer a chance to advance timing. changing the timing to the most accurate curve of combustion in your combustion cycle allows a more powerful burn. lower octane rating fuels detonate sooner than higher fuel grades. they burn at the same rate, and normally hold the same longevity. but changing the timing at which the fuel and air is accepted provides for horse power.

i agree that putting a over the counter octane booster in your tank in any octane fuel is not worth the bang for the buck, but a home brew booster in any octane is a real and feasible thing. notice that the ether is just like i said the best booster available.

i got this from a quick search on home brew octane boosters it was posted in the clubWRX.com forum. the two boosters that are listed that have a percentage that is not recommended i recommend you not use them at all. it if ruins your engine at that percentage, then its probably hurting your engine at the recommended level as well.

Formula #1 - Toluene
R+M/2.........114
Cost...........$2.50/gal
Mixtures with 92 Octane Premium
10%...........94.2 Octane
20%...........96.4 Octane
30%...........98.6 Octane
Notes: Common ingredient in Octane Boosters in a can. 12-16 ounces will only raise octane 2-3 *points*, i.e. from 92 to 92.3. Often costs $3-5 for 12-16 ounces, when it can be purchased for less than $3/gal at chemical supply houses or paint stores.

Formula #2 - Xylene
R+M/2.........117
Cost...........$2.75/gal
Mixtures with 92 Octane Premium
10%...........94.5 Octane
20%...........97.0 Octane
30%...........99.5 Octane
Notes: Similar to Toluene. 12-16 ounces will only raise octane 2-3 *points*, i.e. from 92 to 92.3. Usually mixed with Toluene and advertised as *race formula*.

Formula #3 - Methyl-tertiary-butyl-ether (MTBE)
R+M/2.........118
Cost...........$3.50/gal
Mixtures with 92 Octane Premium
10%...........94.6 Octane
20%...........97.2 Octane
30%...........99.8 Octane
Notes: Oxygenate. Very common in octane booster products. Has lower BTU content than toluene or xylene, but oxygenate effect makes the gasoline burn better and produce more energy.

Formula #4 - Methanol or Ethanol
R+M/2.........101
Cost...........$0.60 - $1.75/gal
Mixtures with 92 Octane Premium
10%...........94.3 Octane (Methanol)
10%...........94.7 Octane (Ethanol)
20%...........Not Recommended
Notes: Methanol is wood alcohol. Ethanol is grain alcohol and found in Gasohol in 10% ratios. Both alcohols are mildly corrosive and will eat gas tank linings, rubber and aluminum if used in excessive ratios. Main ingredient in "Gas Dryers", combine with water.

Formula #5 - Isopropyl Alcohol and Tertiary Butyl Alcohol
R+M/2.........101
Cost...........$0.60-$1.50/gal
Mixtures with 92 Octane Premium
10%...........94.5 Octane
20%...........Not Recommended
30%...........Not Recommended

its basically saying that the MBTE ether is the best to use due to its oxygen compound. although the heat produced from toluene is higher which to me seems just like your average problem in the future if your going to constantly use it. the oxygen in the ether allows for a more thorough burn without adding more heat.

i did the math on the G3 eclipse which claims a fuel capacity of a 16.4L fuel tank. it comes to 1.64 gal. for 10%, 3.28 gal. for 20%, and 4.92 gal. for 30%

over the counter octane boosters are crap. but the homemade boosters are the BOMB BAIT!!!!!!!!

Thanks for the response, great answers, just what I was looking for(and more:p) Looks like I'll be running the 91 $tuff, I think that's about as good as I can get around here. Pricey right now though, we're gettin' $crewed on fuel taxes :(. For no good reason either. Oh well, I guess I'll just pull out my wallet and bend over... lol

Thanks again.

Still they don't do hardly anything like they say they're gonna do for you. You pay the extra money for another 1 octane rating at the most. and it's stupid. He needs to just go get 91 from the pump cause he's looking for the cheapest and simplest way of doing things. And buying premium from the pump is the best option.

Cause like I said I've tried an octane booster once and my car ran worse than it did on just 87 octane gasoline.

the other thing is, SkRibL77, some stations have 93 octane rated gasoline at their pumps. So if you ever come across a station with some go ahead and fill your car up with it cause it's usually not any more expensive than 91 and if it is it's no more than 5 cents more and you'll get a tiny bit more performance and the same gas mileage out of it.

up here in NW OHIO all staitions have 87..89...93 all with 10cent increments..so to fill up(16 gallons) w/ 93 (opposed to 87) is $3.20 more.. i dont think thats to bad.

No it's not bad, even though down here in STL Mo it's in 15 cent increments so on average it's roughly 4.00 more to fill up and ours is mostly only 91 but there are a few that have 93. But wouldn't you say that's his best bet instead of using crappy octane boosters.

WOW.
lower octane just can cause(PINGS) RARE/