87 octane vs 89 octane
 

To be honest, I'm not a gear head, I'm a computer nerd. From what I'm told this is pretty straight forward, I just want to make sure thats the case.

I recently (a day after I joined the forum) filled up all but about 3 L of my tank with 89 octane. I've been told that depending on the car, it can make a big or small difference. so far, Ive gone through roughly 34L of my tank and I am at 400 KM, making it 8.4 L/100KM (27 MPG) which is WAY better than my previous 13 L/100KM (18 MPG). So far it looks to be worth it.

Would you guys say that generally 89 octane gives substantially better results? Is it worth the money filling up on it every time? Or do most of you guys use 87?


Note: this gas is also rated to be up to 10% ethanol.

yeah i know its a noobie question but hey, you gota start somewhere.

I would say to stick with what your car was built for, as timing and all that is optimized for a certain octane.

Can it have adverse affects if you use it consistently? I did notice that in drive I go faster with no throttle...

I don't think it would have adverse effects, but most people who use a different octance will report lower FE...then again, every car is different.

Lower FE than 87? Or lower FE per cost?

Looking at Wikipedia for Fuel injection etc, it looks to be fairly safe since the engine would compensate (according to Fuel Injection). As for belts and such (of which I don't know much about), I don't imagine anything really would change, its all very static.

I seem to be getting some great numbers from this gas though, and the performance is clearly different (albeit still crappy ;) ).

I've always used the lowest octane that my car used w/o knocking. In some cars that meant regular driving through Indiana and premium in Vest Virginia. I never noticed a chang in mpg that couldn't be attributed to terrain and/or traffic. But if it is getting you better FE I say use it until the tank before your e-check if you have one.

Don't make conclusion by filing one tank only. You get better FE, not ONLY because of switching octane. Maybe you drive on different routes, at different speed, in different mood or that pump fills your tank more than the others(so you can go further). Try at least 3 tanks. If you get 50%+ FE consistently, then keep using 89. Maybe you should try 91 later for even better FE. But, for my car, getting 40mpg with 87 makes me happy already. I don't expect it will get 60mpg by switching to 89 or 91.

I agree that it could be attributed to terrain but my route doesn't really change.
Yeah I will definatly be continuing the experiment. The plan was 2 thanks 89, 2 thanks 87. But I've measured my milage before and really only get around 10-12 L / 100 KM regularly. This is why its odd to have such a dip in consuption, and the only change really seems to be the octane.

I will test it however :).

But is it really a problem? A friend of mine had a 92 Acura, and it wanted 89. When he did run on 87, his efficiency went down (not noticable) but he said it was more worth it to go with 89. And again, a friend of mine with the exact same car who drives alot noticed this as well. They dont measure as closely as you guys of course.

I buy the cheapest gas around because I know as well as the next guy that its all the same dead dinosaurs, and I was even skeptical about this higher octane (I bought it cause it was on sale, it is every thursday night). I just find it odd that I show such a drastic increase with just 1 tank. I was even kinda heavy on the pedal since I had more accelerating than usual to do.

EDIT: And just an add, my engine does seem to kick a bit less than when I used 87 (and i've never used 89 before). The difference in performance as well was only in the lower end of the spectrum, I still need about 2.5k revs to keep it at 60 mph.

The octane ratings on the pump are minimum ratings. It's possible that if they are mixed with 10% ethanol, the 87 and 89 are both about 91 anyway. The change in mpg is almost definitely due to something else.

I guess we'll see once I fill up again.

Well the idea of posting this WAS to burst my bubble if I was wrong, and hey I very well could be. We'll see next tank of gas

my car used to ping like a mofo on 87 at part throttle but went away when it was floored. the 89 cured the part throttle pinging. if i drove very gradual which isnt as efficient and do not load the engine, it didnt ping with 87 but i do need to accelerate quite often. the price betwen grades is a dollar per tank give or take. if you have any audible ping with 87 you need to lower your timing or clean your combustion chamber. if you can hear pinging your engine was getting damaged way before that. i come from the boost side of fun so even 91 in my other car is substandard.

my mileage got better in the aspire with the lower octane but its because i had to change my driving practice to not detonate. no spirited driving. newer cars have sophisticated knock sensors that pull timing when knock is occuring but less timing means less power. your 'pulse' wont be as good as if the engine was operating perfectly.

Here is my take...with 35 years of drag racing street driven cars:

If your car does not require premium and the timing is stock you can actually get worse mpg with higher octane, The higher the octane, the slower it burns....a lot of cars drag raced with premium fuel will actually run slower and have less power. Just run reg if your car calls for it.

As far as running 87 in a car that requires 92.....on my 05 SRT4 Neon (230 hp 2.4 turbo bone stock) I WAS running 87 when I first got it. On my 80 mile loop that I use for mpg comparisons I got only 27 at 55-60mph while it was rated at 31. I even fill up at the same pump and put it on slow speed till it clicks off...not a penny more...then with 92 oct I then got the 31. That car now gets 32.8 with a stage 3 set up that developes 285 hp!

As far as 10% ethenol is concerned.....you might get as bad as 20% WORSE mpg since more fuel is needed to obtain the same driving parimeters. I read in a magazine last year that E85 can be as bad as 27% worse than straight gas and on my flex fuel 01 Caravan it did get @ 25% worse on E85 compared back to back with reg 87 oct gas.

Guys that convert their drag race cars to alcohol must increase the jetting in their carbs by about double for the same power levels, but then they benefit from a cooler running motor and can mofify them to run more compression and or boost.

That first tank was awful low at 18mpg as compared to the epa numbers. I bet you filled the previous tank on the uphill side of the pump and did not pump it as full as the current one. Todays gas tanks are pretty flat and it can make a big difference which side of the pump you fill from.

In my old corrolla, 87 and 89 were about the same MPG and 91 5% worse. I ran 89 cause it would never ping that way and I figured retarding the timing would be worse for MPG

In my current CRX HF the gas mileage at freeway speeds is pretty much the same for all grades, but at low RPM cruising, 45 MPH, 5th gear, 1400 rpm for example, there seems to be about a 5% increased MPG per grade according to my supermid and my last 3 tanks.

I have seen octane make a difference while towing. With higher octane I get a little better FE if the weather is over 85 degrees. I think my '88 Ford does a poor job of adjusting the timing for hot weather, it senses detonation and pull sout 10 degrees or something, and really runs bad. The ECU might be dumping in 10% more fuel as to cool things off, as well? So on that particular vehicle, it makes a difference.

Just know that higher octane gasoline has the same BTUs as lower octane gas. Higher octane than required will actually reduce engine power.

But thats at the high end. I doubt that I will see much of a difference on highway driving (infact my trip to Montreal showed that it doesn't make much of a difference, I got slightly over EPA). It might be a slower burn but its a bigger bang, I don't see how it would hinder low end MPG. Might muck with the timing but again, its the physics I know, not the engine stuff.

Yeah that was the worst fill I've ever seen, but i used the same pump as I did for these past fills so who knows what it was.

Sorry to necro post but I wanted to update. While my fuel log is all over the map, I'm getting about 25 mpg with regular. I'm going to try 89 now, especially now that gas has come down.

I used a tank of 91 octane in my '88 Escort that calls of 87 a few weeks ago because I couldn't get the 87. My driving habits and routes are about the same day in and day out and I didn't see any FE benefit although I could tell the car had more power.

If you don't change the timing of your vehicle, I can see where some will say that increase in octane sees little results. BUT, if you were to use 91, then adjust timing to where it just stops pinging, then you should see enough of an increase in FE to justify the expense. I did the math and found that by doing just what I said, 91 octane is more than worth using for increased FE.

With 85 octane, I get 54 mpg (+5 deg timing). With 91 octane, I get 60 to 61 mpg (+10 deg timing). It costs me $.065 per mile in fuel with regular and $.060 per mile with premium. My break even mpg would be 57 mpg. Anything over 57 on premium makes premium fuel the least expensive.

Using regular 85 octane, it will cost me $142.19 per month in fuel over 2200 miles.
Using premium 91 octane, it will cost me $133.08 per month in fuel over 2200 miles.

87 octane puts the numbers about midway.

I can't make it any clearer.

When I used to tow with the 6000 wagon, I would make it a point to put in 93 octane because it gave more power as well as reduced pinging. It made a difference without towing too, on the large hills that are on my way to and from work, but I would just use 87 usually because I didnt really need the power that bad. But the engine also had well over 200k on it. I figured that the added octane wont really give you more power than stock, but it will help compensate for the loss of power in a well worn high mileage engine.

Earlier this year I tried 93 octane for a few downstate tanks in the Celeb. I noticed no difference in mpg.

For me I don't ping on either octane, and I do feel the increase in power right away. But most importatnly it looks like I get better millage without any adjustments, and thats what I'm going for. I'll try it and see.

I agree. I have a 95 volvo 850 wagon. If I run 87 in it in a matter of minutes I will stall at every stoplight or stop sign. If it calls for 87 run 87. If it calls for 89 run 89. I work in a small engine shop and we have seen a lot of engines vapor locking on hot days due to the lower boiling point of ethanol.

I have a 96 volvo 850 wagon with 195k miles on the odometer. The owner's manual calls for at least 91 octane. I run it on 87 octane almost exclusively after testing every octane I could find repeatedly over multiple fill ups. There is no difference in power and a slight improvement in fuel economy with 87 octane. If you 95 volvo stalls on 87 octane, there is something else wrong with your car. Probably the thermostatic intake mechanism.

Lets see, adverse effects would be, lets think, fuel burns slower, timing is the same, so we get fuel left over, right, you following me so far, and unburned fuel turns into what??? I know you know this, carbon. And carbon deposits do what? Make the engine run less efficient:thumbup: Or so they say. I say carbon deposits on pistons would raise the comp ration, which will make it run more efficient, but you would need higher octane.:D

You do need 20% more e85 than regular gas, which why some people hate it, but man it's great for forced induction cars, e85 is like racing fuel only half the price:thumbup:

Is your 850 turbo or non-turbo? Mine is the non-turbo. I love the car though...300 thousand miles and still ticking.

Kind of a leap to conclude that if E85 (roughly 85% ethanol) drops fe "27%" that E10 (roughly 10% ethanol- 75% less than E85) yields only 7% different results??? I've never experienced anywhere near a 20% fe drop because of E10.

Not strictly true. In fact, I know several petrochemical engineering types who insist that the flame-front speed is more dependent upon cylinder pressures and mixture than upon the fuel composition. At least, in any gasoline we would see sold for street use. (Ethanol will change things; I am not sure how much.)

As a counter-example, there are known cases of aviation engines who suffered burned exhaust valves from running 110-octane Av Gas when they were designed specifically for 80-octane Av Gas. Those seem to have been caused by the mixture still burning as it exited through the exhaust port. But that's a much larger change in octane than we see in streetable motor fuels, and Av Gas is not really the same as automotive-grade gasoline.

-soD

Sometimes older engine need higher octane because of carbon build up.

Just get all of it out of the lines after teh race.

is Octane a Universal rating?? just I think we're a it spoiled over here our 'regular' is 95Oct and 'premium' 98-99 depending on supplier. in previous cars i have noticed FE increases on AA-BB-AA-BB tank fulls of reg / premium. Sadly due our unelected dictatorship taxing us soooo much and the margins the oiler but in, that although mpg is increased cost-per-mile can be lower and at the end of the day thats what I'm after PPM (pence per mile, how old skool!)

Psychologists know that something called head-factors bias experiments all the time. It is almost impossible for humans to not unconciously bias results. The only way to know is to get your wife to fill up with either 85 or 87 octane, write down which, and then not tell you. After a few months of recording mileage unbiased by your expectations you can "open the sealed envelope" to see if octane really made a difference.

Agree. I can't find it now but a recent technical study of various ethanol blends showed that all cars have sweet spot ethanol blend where mileage is at its maximum - higher than either pure gas or E85. Some crs showed significant improvement at their sweet spot, others only a small amount. They tested several cars, including some that were not flex fuel. Sorry I don;t remmeber details but sweet spots were generally between E25 and E40. Maybe someone can find it with google.

Non turbo. Check this out
http://www.matthewsvolvosite.com/for...&sd=a&start=56
You'll most likely pickup some MPGs in the process and you should be able to run on 87 octane most of the time without a problem.

No. In the US octane is calculated by the formula (RON+MON)/2. In the UK and most of the world its simply RON.
http://en.wikipedia.org/wiki/Octane_rating

Our 87 octane is equivalent to your 91-93 and our 92 is around 95-97 in the UK. Generally speaking the US has lower octane gasoline than the UK and europe but the difference is not as big as the raw numbers would suggest.

Study Finds Certain Ethanol Blends Can Provide Better Fuel Economy Than Gasoline | Auto Newswire Article from Motor Trend

Wow!!!

I might have to try out some different blends to see if I can make some improvements.

I already have a 55galllon drum of E85 I use for racing.;)

Nice find!!!!

in the motortrend article i dont see where it says anything about more / better mileage.

Previous assumptions held that ethanol's lower energy content directly correlates with lower fuel economy for drivers. Those assumptions were found to be incorrect. Instead, the new research strongly suggests that there is an "optimal blend level" of ethanol and gasoline--most likely E20 or E30--at which cars will get better mileage than predicted based strictly on the fuel's per-gallon Btu content

this sounds like a fancy way of pushing ethanol with new and improved "less loss than expected"

Jeezus, you didn't even read it didja? :rolleyes:

I use to drive a 26cc stand up scooter with a Tanaka engine. It would run on standard 87 fuel, but I typically ran it on 98 octane + octane booster, aprox 100 octane. It definitly ran about 2mph faster with the higher octane.

With that said, I know where talking about cars mostly, but every engine is different and if MPG is different that will depend on the compression ratio of the engine etc.

nope, didnt, looked like re hashed version of

http://www.ethanol.org/pdf/contentmg...yStudy_001.pdf

back when it didnt work for em at all except with some wierd denatured alky/biodiesel stuff i've never heard of....
...but now i see they have

http://www.ethanol.org/pdf/contentmg...inal_12507.pdf

now they think they have something but they dont... they forgot to bring a gm tech to thier tests...

theyre excited about a chevy that cant handle the test because they dont use actual fuel sensors anymore, and only recalibrates to adding e0-e10 or e85, it cant handle adding mixtures in between, you can drive on e10, add some e85, and have a tank of e30 just fine.... but dump in e30, what will happen isa crapshoot.


from gm SI fora 07 impala
E85 Flex Fuel Description

E85 compatible vehicles no longer use an alcohol sensor to determine and adjust for the alcohol content of the fuel in the tank. Instead, the vehicle calculates the alcohol content of the fuel through measured adjustments.

The ethanol calculation occurs with the engine running after a refueling event has been detected via a measured change in the fuel level sender output. The virtual flex fuel sensor (V-FFS) algorithm temporarily closes the canister purge valve for a few seconds and monitors information from the closed loop fuel trim system to calculate the ethanol content. This logic executes several times until the ethanol calculation is deemed to be stable. This may take several minutes under low fuel flow conditions such as idle, or a shorter time during higher fuel flow, off-idle conditions.

Air-fuel ratios and the corresponding ethanol percentage are updated following each purge-off sequence. the fuel alcohol content percentage value can be read on a scan tool.

When an E85 compatible vehicle is built, an ECM replaced, or if the learned alcohol content has been reset with a scan tool the fuel system will need to contain ASTM gasoline with 10% or less ethanol content.

A minimum of 11 Liters (3 gallons) must be put in the tank in order for the vehicle to recognize a re-fueling event. It is not necessary to turn the ignition off in order to have the re-fueling event recognized; however local safety regulations should be followed.

After the re-fueling event, the system registers the amount of fuel that was added, relative to the amount that was in the tank. Reading fuel trim and O2 sensor activity, the system determines if the fuel added was either ASTM Gasoline or ASTM E85. Based on that determination, the system adjusts to the expected alcohol mix in the fuel tank, and then the fuel trim and O2 sensor activity fine tunes the adjustments. The system must remain in closed loop in order for this adjustment to occur. Numerous short trips after switching from gasoline to E85, or E85 to gasoline, can result in driveability symptoms due to the inability of the system to adjust for fuel composition by not attaining closed loop operation.