Using Premium Gas

[MOAK]

For years and years now I have been reading, nearly everywhere, except the "Novak" website, that using premium grade (91 and above octane) gasoline in an engine that requires only low octane gasolines, is a complete waste of money, as the MPGs don't improve, nor does performance. So I never bothered to even try it out, until yesterday. I topped off with 8 gallons of premium, before our 120 mile round trip to REI, north of Philadelphia Pa. I usually average, 16 mpg empty, just my gal and I. When my fuel gauge reads 3/4, It has traveled 50+/- miles.
So. 3 very important things happened yesterday while using the premium fuel blend. My throttle response was obviously much lighter. Traveling, up a long, slight grade, at interstate speeds with a headwind, I found that I did not have to floor the pedal to maintain highway speed, in fact, I had to keep backing out of it. Normally, its floored, and sometimes with a bit of a load, down shift to maintain 60 mph. When my fuel gauge reached the 3/4 mark, we had travelled 72 miles instead of the traditional 50 +/- miles. I'll check the real MPGs next weekend when I fuel up again, but I'm pretty sure, judging by the fuel gauge, that I'm getting substantially better MPGs. I know for sure I have more power. I think this is a worthwhile conversation to get started, as I am curious about every one else's experience. If the math works out, I may well be switching over to premium grade gasoline, provided there would be no long term damage to my engine. Looking forward to all opinions and or researched facts on this matter... Thanks all !!

 

[Calin.Macrinici]

I'm not sure how much ethanol you normally get mixed in gasoline in your area. Around here the percentage varies between grades of fuel, usually the premium has the least or no ethanol mixed in (and I believe the content also varies between summer and winter fuel). Since we all know that ethanol reduces the energy output of the fuel, that would be the most likely reason for the increased everything (power and MPG). I know this can't be 100% true, but probably even regular gasoline with no ethanol mixed in would bring about those enhancements on its own.

 

[postalWagon]

It all depends on your engine condition. My '75 does not eat "premium" fuel, because the carb is tuned to run on 87 or less. Thats not to say that I don't "blend" grades to clean up any deposits that might be in my lines. It may just be that your jeep needs "premium" fuel ever once in a while.

 

[Septu]

I'm not sure how much ethanol you normally get mixed in gasoline in your area. Around here the percentage varies between grades of fuel, usually the premium has the least or no ethanol mixed in (and I believe the content also varies between summer and winter fuel). Since we all know that ethanol reduces the energy output of the fuel, that would be the most likely reason for the increased everything (power and MPG). I know this can't be 100% true, but probably even regular gasoline with no ethanol mixed in would bring about those enhancements on its own.

I second this theory. I ran 91 in my 07 JK all summer and would get 10-15% more out of a tank. However 87 use's 10% ethanol, and 89 is a blend and no one will say exactly how much ethanol is in there (the label still says there could be up to 10%). I checked with the gas stations/head offices and found at all the 91 gas up here is ethanol free. I'd love it if there was a place that sold ethanol free gas near by.. but there isn't. I haven't tried 91 in the new JK yet... and I probably won't anytime soon.

 

[4lowdean]

In my stock 160k+ mile 4.0L I run mid-octane gas and see about a 10% increase in MPG over low-octane gas. If I was running a better exhaust, better intake, and some nicer plugs (and maybe a chip) I would probably run high-octane fuel.

Back in the day when gas was $1 a gallon the 10-20% jump in price to switch to the higher-octane fuels wasn't really worth it. Now with the price jump only being about 2-3% (since the price gap between grades is still about 10 cents despite the rise in gas prices) it makes a little more sense. Also the ethanol blend in the lower octane fuels is ******** for older motors so the bump to at least mid-octane gas is a major bonus for anything 10+ years older.

I could whip out my tin-foil hat and share some disturbing observations a friend of mine has made surrounding ethanol being near 30% at the pump in some areas... but I think ExPo is not the best place for such conspiracy theories. eepwall:

 

[jeep-N-montero]

Higher octane also allows the engine to run at its peak timing curve without knock retard.

 

[nxski]

Put in regular gas and add some Petrolabs or similar and voila, premium gas at a fraction of the cost.

 

[DEnd]

Holy carp there is a lot of BS in this thread.
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First of all if your engine is not designed to run "premium" gas you will not see better mileage, or more power by using a higher octane gasoline, as long as the engine is in halfway decent condition. If you are indeed seeing a fuel mileage increase from a higher octane gasoline then you have some major carbon deposits that are greatly decreasing the efficiency of your engine, or, as has been correctly stated, the higher octane fuel has less ethanol in it. (Though a higher grade gasoline does not necessarily mean it is lower in ethanol)
.

Secondly you cannot tune a carb to require a higher octane fuel. There are only two factors that determine the octane rating of an engine. The octane rating of a fuel only determines what temperature and pressure the fuel spontaneously detonates at. Therefore the only factors that determine what octane you can safely/efficiently run in an engine are dependant on the engines design as well as the operating conditions of the engine. For example an engine with exhaust gas recirrculation (either through a EGR valve or valve overlap) reduces the temperature of the pistons and valves (in particular the exhaust valve), and the cylinder lining, this reduction of heat held in the engine results in an engine that can have a slightly higher compression ratio while using the same octane rating of fuel. Similarily an engine operating on the top of Mount Everest in the middle of winter only needs a lower octane rated fuel compared to it operating in Death Valley in the middle of summer. The difference that leads to this is not just the temprature difference but also the air pressure. Yes the compression ratio does not change but since the engine starts off with a different pressure the ultimate pressure the engine sees is different as well.
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Ignition timing is often brought into conversations of which octane fuel to run, however "ideal" ignition timing (the timing of the ignition that results in highest power output) is mainly determined by the size of the combustion chamber, the speed of the fuel's flame front, and the engine's RPM. The Ideal ignition timing is at the point in which the peak internal cylinder pressure happes at a point some time after Top Dead Center (TDC). Advancing the timing so that it is farther Before TDC results in an increase in ultimate internal cylinder pressures, which means you need a higher octane fuel to prevent detonation. The point is the most efficient timing has nothing to do with the octane rating of the fuel, but the octane rating of the fuel does allow you to reach that point, and if that point is at say 87 octane then a 93 octane fuel will do nothing to increase the performance of the engine.
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As For PetroLabs stuff, Firstly I would be very hesitant to add any ethanol product in today's fuels, almost all of the chemicals you buy will actually lower the amount of energy available per gallon of fuel. Secondly most additives cost a lot more than just using a higher octane fuel.

 

[JPK]

Higher octane also allows the engine to run at its peak timing curve without knock retard.

Only if the computer has a higher octane "map" and only if the sensors are set up to take advantage of the map.

Ethanol improves octane but reduces potential energy per gallon. A poor way to improve octane.

Here our fuels have minimum ethanol requirements. Used to be winter only but now its year round. Changing octane doesn't impact power or mileage, except in summer when temps are high and you're towing or hualing a lot of weight, then the power gain - really reduced power loss through less or no computer retarded ignition timing - can be noticable.

But when I drove across the country out of liberal lala land and into the real world (and into the world of real gasoline,) I definitely notice both a performance gain and a mileagle gain, and the mileage gain is substantial, like 3mpg, which is on order of 20%.

JPK

 

[Calin.Macrinici]

But when I drove across the country out of liberal lala land and into the real world (and into the world of real gasoline,) I definitely notice both a performance gain and a mileagle gain, and the mileage gain is substantial, like 3mpg, which is on order of 20%.

JPK

What is this "real world" place you talk about, this is the stuff of legends, I'd like to go there too sometimes The "liberal lala land" is encroaching! We even got to the point where my 2005 LJ spits fuel on every fill-up and Chrysler refuses to fix it, their response is "the plastic fuel filler tubes components deteriorate faster in areas with a high ethanol content in their fuels". So there you go, I really need the location of that "real world" place, better mileage and power or not, my Jeep needs it!

 

[lbarcher]

Funny, the owner's manual for my 09 Wrangler specifically states that using high octane fuel may damage the engine.

If I remember correctly, my 01 Tacoma calls for 87 octane which is regular grade here.

 

[MOAK]

Ok, filled it up again, and with that tank of premium, 134 miles, mixed driving, I got the best MPGs ever. 18.5. I attribute this result to less/or no ethanol in the premium fuel.. Liberal la la land,, this forum is not for uninformed, nor informed social/political viewpoints. I do know, that once I cross the Mississippi River, heading west, into our heartland/ethanol states, I averaged less than 12 miles per gallon. Here in my la la state the mix is no more than 10% ethanol, running regular ethanol mixed gas is currently costing me 23+/- cents per mile. Running premium, costs 21 cents+/- per mile.. So my next question,,,, will running the higher octane gasoline damage my engine over the long haul? BTW,,, my engine is clean as a whistle.

 

[4lowdean]

Yes, running a "stock" motor at a higher octane rating is not really a great idea. Which is why I qualified my statement with mods like intake/exhaust/plugs/chip/etc. Also, IMO a motor well over 150k miles is no longer "stock" either and just the added bump from 87 to 89 (low to mid in my area) is enough of an improvement for me since the higher octane fuels also have some 'extras' in them (such as stabilizers and detergents, but that varies by station chain) that low-octane fuels don't get. Also, where you live in relation to sea-level will have a lot to play in that as well. I know in the winter (colder denser air) my Jeep loves the higher stuff (although I never did a focused experiment with 89 vs 93 in my Jeep) vs in the summer when it gets hot I don't see as much of a change. The Jeep 4.0 has such a beastly compression rating that it will run on the higher stuff better than some other engines like a 4cly honda motor or a v6 ford motor. Not so sure about running high-test stuff in a JK motor though... probably not a good idea.

As for "at the pump/in the tank" additives, the only stuff I put in my Jeep is Lucas Fuel Treatment or 'Dry Gas' (but that is only in the winter or when it is really really wet out).

 

[JPK]

What is this "real world" place you talk about, this is the stuff of legends, I'd like to go there too sometimes The "liberal lala land" is encroaching! We even got to the point where my 2005 LJ spits fuel on every fill-up and Chrysler refuses to fix it, their response is "the plastic fuel filler tubes components deteriorate faster in areas with a high ethanol content in their fuels". So there you go, I really need the location of that "real world" place, better mileage and power or not, my Jeep needs it!

I'm not sure where Mississauga, ON is in relation to where I live, but I live within a mile of the Washington, DC line, and Washington, DC has become the epicenter of liberal lala land. And I live in MD, which ought to be referred to as the People's Republic of Excessive Liberalism.

Just so others know how the excessive liberalism and gov't intrusion relates to this fuel and mileage thread, MD, along with a handful of other left leaning NE'ern states have been the force behind "50 state legal" vehicles as opposed to vehicles meeting federal standards and letting the California Air Resources Board do it's own thing. MD is no massive corn state, but we have eager state adoption of 10% ethanol fuel. First in winter and now year round. So poor mileage from a fuel that is fuel intensive to make to begin with. Everyone does know that it takes less energy, i.e. less fuel, to make a gallon of gasoline than a gallon of 10% ethanol blend, right? And then that gallon of gasoline has more potential energy than that gallon of blend, right? Like it or not, the liberal social and political veiwpoint is what has brought you poor mileage, more pollution and poorer performance through ethanol (of course the generally conservative farmers aren't fighting back, since the ethanol coercion is good for their wallets.)

 

[HonesT]

I own a 1997 stock Cherokee XJ, I use chevron gas and was getting 380 km per tank on the grade above the lowest, then a friend told me I was waisting my money so I tried the lowest grade gas and now get 320km per tank.

My 93 acura integra had only 1 fuel injector for all four cylinders so I had to run the grade above the lowest or it would sputter and act up prob due to the lines getting gunked up, My jeep has multi port injection, (injector for each cylinder/so this also means more pressure pushing so running the cheap gas did not affect performance in my Jeep just mileage.

The higher grade will greatly improve hwy mileage & not so much in stop and go traffic.

Love people who try to drowned out the smart imputs people make online. wonder if Global warming would be happening if they had just kept there yap shut :snorkel: