Gasoline grade and performance

[TheGoodShepherd]

For the record we have an '05 Forester and a '14 Forester.

 

Simply wondering if there's ever reason or advice to use gasoline rated higher than "Regular" 87 octane. This would be for either or both cars.

[Fairtax4me]

For a Non-turbo engine, no reason at all.

 

Higher octane Might get you an extra MPG or two if you drive with a heavy foot, but its usually not worth the cost.

 

There are usually more detergents in higher octane fuel that keep things like injectors and valves clean, but you can simply add a bottle of fuel system cleaner once every 3-6 months and accomplish the exact same thing. I buy the quart size bottle of Lucas fuel system cleaner when I can find it on sale and use about 3 ounces in the tank every three months or so. Between the 4 cars I maintain for myself and family, a bottle lasts me about 9 months. I got it last time for about $12.

[01 Outback]

My 01 gets 1.5 to 2 MPG better with premium that 87. Not enough to offset 40 cents different in price per gallon. I am averaging 23.5 MPG on a 122 mile daily round trip commute at mostly 80 MPH.

[Bushwick]

Turbo engines and higher compression NA engines need it to prevent detonation. Newer, higher compression engines have sensors that can detect the grade and adjust timing accordingly, but you loose significant performance as it pulls so much timing to compensate, which means you'll be pressing the gas pedal harder to make up for the sluggishness.

 

I've also noticed better MPG with 91-93 octane and run it regardless now due to having the better response. Times I've run 87 in the Subaru, it seems to burn through it too quickly. Performance between the 2 in stock, lower powered engines won't be noticed in regular driving, if at all.

 

 

Try this, run the tank down to almost empty (don't run it hard when low) then fill the tank with 87 and reset the trip odometer while noting how much fuel you put in. Drive the car normally, and avoid excessive idling as that'll skew the results. Try and get the tank down to the same point as before (like maybe use the fuel low light if it has one) and jot down the trip mileage along with the amount you added and this time add 91 or 93 octane and repeat the test, while trying to closely mimic the same drive style. That'll ballpark your MPG differences.

[fishy]

Your rigs are modern enough that they're both designed to run on regular fuel AND have sensors and mapping to keep them from knocking and pinging if they get a bad batch or a funny load situation. Aside from boosted or very high compression engines there's really no reason to the high-test in normal cars. 

With that said I _do_ run a tank of premium through my 05 Outback a couple times per year just for the higher level of detergents and unicorn magic but I only do it when the prices are good.

For my lawn equipment, however, I only run premium fuel because around here that's all I can get without ethanol in it (I won't go into that rant here).

 

[idosubaru]

www.cars101.com - are those cars supposed to have premium?

 

i don't think they are.  an engine is either designed for it or it is not.  otherwise there's no benefit.

(unless you're going to crack the code and plan on advancing ignition timing manually yourself to push the limits?)

 

I never run premium.  I have tried on ocassion, i think my EZ30's are "recommended premium, but not required"  and notice zero benefits, even when towing loads well in excess of the towing capacity.  Without any physical reason, I see no need to run it personally.

[Bushwick]

For my lawn equipment, however, I only run premium fuel because around here that's all I can get without ethanol in it (I won't go into that rant here).

 

 

Years ago I had a huge yard that would jump to 6-8" or taller by the time to cut occurred. I originally ran 87 in my 4.5 hp Briggs and Stratton push mower which was new at the time. It had a hell of a time getting through the grass which also seemed to have excess moisture constantly. Even running w/o a bag and letting clippings blow, it bogged constantly. I modified the plug's arm by filing it back a little past center of electrode (this is a known racing trick from years gone by and many plug companies have actually incorporated it into some modern plugs as it unshrouds the spark and all but eliminates hesitation)  and ran premium with a small amount of octane booster if the grass was wet and over 6", or just ran 93 if it was dry. That little B&S engine went from stalling every pass to just obliterating the grass. Only time it'd even come close to stalling was 8"+ wet grass.

 

Octane does make a difference. It's benefit will be noticed more in higher compression engines that need it to prevent detonation, and most cars will just electronically pull out timing for 87. Less timing = a lazier engine. But as with the mower anecdote, it needed to be pushed to it's stalling point to see the benefit clearly. If you barely press the gas pedal, you'll most likely not tell the difference.

Edited October 27, 2015 by Bushwick

[Loyale 2.7 Turbo]

Sadly, in Honduras, the Higher octane Gasolines, barely reaches the amount of octanes found on the Lower octane Gasolines that you have in USA, and we call that, the "Super" ... ... and then, comes the "Regular" that is lower than the Lower octane Gasoline offered in USA ... ... those are the only two options we have here; but once upon a time, long years ago, we had a Third choice, named: "Gasohol" which was a crazy Gasoline / Alcohol mixture, with even lower octane, that the engines almost vomited...

 

That being said, I noticed that my Wife's M.P.F.i. engined car, really performs almost the same with our "Regular" and our "Super" Gasolines, however, the car really uses almost 30% more with Regular fuel, than Super for same Mileage, and needs to have the Gas pedal, floored more frequently, to climb hills and pass on Highways... 

 

On my Weberized Subaru EA82 which I run at 20º Timing, the engine develops ignition Noise with Regular, which almost disappears with the Super.

 

My '69 coupe really don't care what it has on the Tank, it always performs Flawlessly, somehow, and all the Measurements I've took, were using this Method...

 

... run the tank down to almost empty (don't run it hard when low) then fill the tank with 87 and reset the trip odometer while noting how much fuel you put in. Drive the car normally, and avoid excessive idling as that'll skew the results. Try and get the tank down to the same point as before (like maybe use the fuel low light if it has one) and jot down the trip mileage along with the amount you added and this time add 91 or 93 octane and repeat the test, while trying to closely mimic the same drive style. That'll ballpark your MPG differences.

 

...as I explained here: ~► http://www.ultimatesubaru.org/forum/topic/101718-kia-sephia-sporty/page-24?do=findComment&comment=1276280

 

Kind Regards.

(Edited to add the Web Link)

Edited October 28, 2015 by Loyale 2.7 Turbo

[Bushwick]

Sadly, in Honduras, the Higher octane Gasolines, barely reaches the amount of octanes found on the Lower octane Gasolines that you have in USA, and we call that, the "Super" ... ... and then, comes the "Regular" that is lower than the Lower octane Gasoline offered in USA ... ... those are the only two options we have here;

(Edited to add the Web Link)

 

You are to the US what the US is to Australia. Australia gets some rather interesting options at their local pumps. Think Germany is similar as they get 100 as premium and like 95 is their regular. Doesn't make sense to be honest as we could have 12:1 engines with 95 and 100 being available.

 

About 25-30 years ago, we used to have access to a I think 105 or 110 octane that seemed to be geared more for high compression cars from the late 60's (older members would know for certain). Usually it was smaller independent gas stations that offered it and now everything is part of a chain company anymore. Hell, there's a private airport locally that used to let you pull up to their pump which ran aviation grade fuel and was about the highest rating you'd find locally. My mom dated a guy with a 67' Vette convertible that had the rare L88 427 and it wouldn't even run on pump. He had to go that airport for fuel (back in 1987-88' which was a different time). Think the only places selling higher than 93 grade are near drag strips.

[robm]

Rather than remembering how much gas you put in last time:

 

Run the fuel level down a long way.  Fill it up till it shuts off.  Then fill it again, till it shuts off again.  (This will add about 1 quart more gas)

Zero the trip meter.

Run the fuel down a long way again.  Use the same sequence to fill it.

Use the new amount of fuel and the tripmeter reading to measure MPG.

 

Don't worry about running it down to the same point.  Although, once you get the hang of the gas guage, you can get it probably gas up within a couple of quarts of the same amount  every time, but for precision, just fill it to the same point every time.  The more gas you put in, the more accurate the MPG will be.

[Bushwick]

Run the fuel level down a long way.  Fill it up till it shuts off.  Then fill it again, till it shuts off again.  (This will add about 1 quart more gas)

 

That's actually a bad idea. It can create too much pressure in the tank AND can flood out the charcoal canister and damage some EVAP equipment, which often won't be readily noticed unless it actually throws a code. Other issues like excess vapors getting created and either pushed into the environment or forced back into the gas station's pumping machine can occur as well. Any weak areas in the filler neck can start leaking raw gas if it's actually too high, etc. In other words, don't do this.

 

It's also pointless to the test as forcing an extra gallon won't improve MPG, it won't do anything helpful and raw gas getting pulled into the evap would actually hurt the test and most likely cause drivability issues.

 

If a tank holds 17 gallons and the light comes on when 2 gallons are left, and you add 15 gallons, you can use that 15 gallon usage with how many miles driven. Having the light come on is more accurate than guessing how much is left as it reads off the float sensor vs. say trying to use the 1/2 tank line on the gauge which can be off by a couple gallons (digital would be ideal as it'd read a more exact amount). So if you go through 15 gallons of 87 and the light comes on, then you add another 15 gallons to try 93 octane and tally the results when the light comes back on, really can't get more accurate than that. You can't just rely on the gas filler nozzle's shut-off feature either as they are designed to sample the fumes being displaced from the tank and shut off when concentration reaches a predetermined level. Some nozzles are more sensitive than others; some are just wonky. But the gas station gauge is at least accurate regardless so knowing exactly how much gas is going in and being used in X amount of miles is key. The very best time to get MPG readings is with cruise set on a long, flat highway as it removes a ton of variables, but you obviously loose city MPG numbers, though if you can set speed to 40 it'll be a little better, but obviously doesn't factor in hills, idling, stop/go, etc. 

[gemologist]

$ vs. Octane vs. MPG discussions have many variables, aka, opinions; including, but not limited too, the laws physics, driving style, vehicle maintenance.

 

Years ago I had a motorcycle that very clearly ran better with high octane Chevron gas. That started me paying attention.

 

The further you drive in a stretch without stopping the better your gas mileage. The more constant your speed, the better your gas mileage—with caveats. Slow down on up-hill grades and gently return to your original speed. Yes the cruise control is used, but I watch the engine speed more and adjust the cruise control accordingly, not allowing it to bolt up hills. The numbers will average themselves, no need to run the tank dry—very bad. Record the gallons and miles every time you fill up. Divide the miles into the gallons. Take those MPG add them up and divide by the number entries on the trip. This equals you mean average. If you are a fanatic—like me—or just bored, you can record the time.

 

My '90 Legacy LS got 37.1 MPG at 62.4 MPH average speed; mostly flat terrain over 1229 miles; high octane fuel; stopping only to refuel. More recently, on a shorter trip, it got 35.2 MPG, high octane fuel. Long coasts to a stop; accelerating slowly.

 

The most expensive part of your drive is accelerating from 0 to 1 MPH. Once you are in motion you tend to stay in motion—it does not cost as much gas to go from 1 MPH to 2 MPH. Accelerate as slowly as traffic will allow. Coast to the limit line; do not rush it. Remember the 'Speed Limit' is a Limit not a Prescription.  Coasting = Positive Infinity MPG vs. Stopped / Idling = Negative Infinity MPG.

 

Apologies for the Rant.

[bratman2]

Most countries use a different method to determine octane rating. I believe Germany and most other countries use RON. We use (R+M)/2 which gives a lower number. Many other countries do not use ethanol also which gives slightly more energy per gal. I have been dealing with a local tire dealer for nearly 35 years that is also a major fuel distributor in eastern NC. They sell me pure 87 fresh from the storage tank for my Brat and 4 cyl Ranger. Using that fuel I have averaged near 1 mpg more and don't have to worry about the ethanol separating out if the Brat sits a little. They tell me pure gas has 3% more energy than ethanol blended gas. If you want more fuel economy and better performance seek out "pure gas" gas stations. They are out there. Sadly the fuel is more expensive so there is little to no cost benefit. In the seventies I had a Yamaha drag bike with very high compression ratio. The engine builder told me to use either Sunoco 260 or Amoco white gas that was available at the time. They were 96 octane for the white gas and 97 for the 260 if my memory is correct. Before those times the US used a different method to determine octane so the higher numbers most likely are not comparable. I remember seeing 100 plus octane as a kid at fuel stations in the sixties but once they went to (R+M)/2 I never saw anything higher than 97 as gas at the pump. To answer the op's question, you will most likely see no real benefit from running premium. You will be a little poorer. Your Forester's computer can make adjustments for the premium but not enough to give a cost benefit ratio that you would see.