Real Deal on Octane

[Nemnith]

Hey everyone. I've heard a few different things about what type of gas people put in their cars. I've heard stuff like "as low octane as possible without knocking" and "higher octane the better." Anyone care to shed some light on exactly which I should be using in my '01 2.5RS? I'm using Super (89 octane) at the moment, but I've been hearing that it's a waste of money. Thanks.

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[joefocker20]

Well, Ive been putting 89 in my car, but I have a PROECM and should be putting in 91 for optimal power. Within the next few months, when I get most of the stuff I want for my car, I'm going to dyno it, and I'm going to put 93 in for that. Put the cheapest gas you can in right now, the prices are outrageous..

[sti27]

Im no expert on gas, but what I learned is the higher octane (92,93,94) will help keep alot of stuff inside the engine clean. Kinda eliminating the need for fuel injection cleaner. My local Sunoco sell GT100 octane fuel and of course I had to try it.
It was $3.50 a gallon(last year sometime, Im sure its more now)
and cost me $25 for only have a tank. Wouldn't recommend buying all the time for the price, but I did notice a difference.

[ciper]

sti27: Although Im a strong supporter of higher octane for some people I think the "cleaner" idea has been proven wrong. The fuels are basically equal in all respects except the higher octane is slightly more stable.

If all you do is putt around using at most 30% throttle 85 octane would probably be good enough.

However if your car calls for 87 and you run it in hot weather at WOT half the time it would still benefit from 92.

What Im trying to say is higher octane may be better but not everyone needs it

[Supraru]

I use moble 93 everytime I fill up. If I switch back my car will probably run crappy. Plus I usually don't put around, I'm always driving hard.

[meZoom!]

(hey my first post here!)

In most Japanese cars I tend to pump in 91 octane (currently the highest available in so cal). My cousin in japan works at a gas station and he told me that the LOWEST octane they sell there is 92 or 93, i forget which, and the highest they sell is 100. keep in mind this is a normal station in a normal town. after hearing that, i got to thinking that perhaps japanese cars, at least, are designed with this in mind.

[JohnP555]

Yeah I as well am not really sure how the octane thing works. I was under the impression that all fuels had the same clean factor and that running 93 in a car designed to run 87, such as the RS, would do absolutely nothing you would be throwing your money away. Anyone have information on any studies done on this or what?

I have run 87 in my car since day one, haven't really felt a need to run a higher octane. Then again I don't putt around town, so maybe I would benefit from an octane increase at the pump.

[zzyzx]

Originally posted by meZoom!
(hey my first post here!)

In most Japanese cars I tend to pump in 91 octane (currently the highest available in so cal). My cousin in japan works at a gas station and he told me that the LOWEST octane they sell there is 92 or 93, i forget which, and the highest they sell is 100. keep in mind this is a normal station in a normal town. after hearing that, i got to thinking that perhaps japanese cars, at least, are designed with this in mind.

In Japan octane is rated in RON. Do a search for explanations.

I collected some data with a data logger at the race track comparing 87 vs. 92 and the timing curves using the stock ECU were more advanced with 92. This was on a '00 2.5 RS.

- Steve

[karl_hungus]

I wouldn't waste the money by putting in high-octane all the time. If you plan to head to the strip or autox and you want more protection against knock then buy the expensive stuff otherwise you're throwing money away.

I've run my car hard in the heat with 87 octane with no perceivable knock... although I got my ECU mapped for 92 octane last fall so thats all I run now.

[Legacy777]

This subject has been beat to death many times on this board and others. There are some basics that need to be understood when "tackling" the octane issue.

The quick answer is that higher octane is not always better, and it will vary for different motors, different ECU's, different driving styles, etc.

Now lets get a little more technical. The octane rating essentially refers to the amount of energy needed to ignite fuel. 92 octane will require more input energy before it ignites then 87 octane.

Most cars are designed to run on 87 octane. They're timing curves and everything are set around that. If you put higher octane in there and the ECU does not know it's higher octane. It really doesn't know it can advance the timing further to get more power and not have to worry about knock.

Yes the ECU can learn over time, but from personal experience and from others that have done similar tests, the extra power that you seem to get from that first tank or two of higher octane seem to go away and your car feels the same. Yes i know that's not a very scientific test, but I know I've done the test several times and every time I come away with the same conclusions.

What auto manufacturers need to do is do what Polaris did on their snowmobiles. Have a switch you can flip that tells the ECU you have premium in, so it can take advantage of the higher octane.

There are few other points I could make, but don't have time for that now.

Personally.....I run 89 octane. The car just seems to run best on it. Don't ask me why....it just does.

Other's may have similar or different experiences with what their cars likes, but what I said are the principles behind the whole octane thing and how the computers are setup.

Josh

[BOY]

Read up: http://www.refiningonline.com/Engelh...ep/TCR4_29.htm

Octane is literally resistance to detonation (any detonation). The higher the octane the harder it is to explode the air fuel mix. RSs were designed for 87 PON (pump octane number or [RON+MON]/2) and will advance timing some with higher octane but unless you're running aftermarket electronics (fuel and/or timing control) or cams/FI your better off rolling up your dollar bills and stuffing them into your gas tank.

[DanzBorin]

Originally posted by BOY
unless you're running aftermarket electronics (fuel and/or timing control) or cams/FI your better off rolling up your dollar bills and stuffing them into your gas tank.

make sure to put some sugar in there too*...



*disclaimer: don't do this, and if you do you are stupid and deserve whatever happens...

[BOY]

Danz talkin trash

[DanzBorin]

Originally posted by BOY
Danz talkin trash

I just had a vision of people stuffing dollars into their gas tank...

I figured if you could talk them into doing that, sugar would be the next logical step...

[Jack ffr1846]

The octane ratings at the pumps are MINIMUMS. A few years ago, it was disclosed by Sunoco that their 86 octane in most markets (including New England) was actually 87. They then removed 86 from all their pumps.

I've run 87 in all my cars for 20 years on the street and 91 or 93 on track days only. Cars have included 90 M3, A4 5valve V6, Dodge Turbo, Honda 1.6L 16Valve. None have pinged or ever had an engine failure. I've saved a lot of money over the years not going to higher octane. In my 91 CRX manual and wife's 91 Integra manual, Honda expressly stated that running anything over 87 octane is a waste of money and will get you no better performance.

When a car says "premium fuel only", it's because they needed it to meet EPA emissions requirements.

jack

[Legacy777]

Just to throw this tid-bit out.....

My car actually seems to have less power with premium vs. 89 octane......so computers/engines will vary

[slowlegacy]

run a tank of 87, 89, and 102 through to see what you think. keep in mind you'd get better performance putting your foot 15% further on the petal with cheap gas than getting gas that costs 15% more.

[slowlegacy]

i said that wrong. if you drive hard enough to burn 15% more gas, the car will definately feel faster

[Legacy777]

I don't quite get what you're saying??

Are you saying that if you put the cheap stuff in, you'll have to push the gas pedal 15% more then what you would with more expensive stuff?

[ciper]

I think he is just crazy.

Ive literally used about 1000 gallons of 91 octane in my Legacy that asks for 87 and I still do it.

[RebelINS]

I have tried running pretty much every octane gas that the average pump offers, and I have never really noticed any difference. Now I just run plain old 87 because I didn't notice any difference when I was running other octanes, plus gas prices a getting pretty high now.

-Wes

[yamahito]

My findings in short:

Lower octane detonates easier, if you put a higher octane it will not detonate as efficiently and may leave carbon deposit buildup in your engine (so actually using higher octane may be more 'dirty' for your engine).

Higher compression engines e.g. WRX are compressing the gas to the point where 87 octane may predetonate (remember, it detonates easier). This is the reason they need higher octane.

Bottom line is that higher octane in an RS will actually make it run less efficient and cause more buildup.

I gathered this info from several mechanics, drag racers, and I was very skeptical, but believed them after reading many articals/ websites on this. There is a pretty good explanation on howstuffworks.com go under auto, then how engine works. Great website.

[RebelINS]

if you put a higher octane it will not detonate as efficiently

I think you misused the word detonation. You don't want more efficient detonation, you don't want any detonation, detonation is bad. I think you meant it won't burn as efficiently, but I am not 100% sure that that is true. The octane number is based on the knocking tendencies of the hydrocarbons heptane and isooctane. Heptane is sort of the base for the scale because it has a higher tendency to knock then normal gasoline. Isooctane is given the octane number of 100 because of it's resistance to knocking in comparison to commercial gasoline. If the octane number is under 100 it represents the percentage of isooctane that is mixed with heptane to give bordeline detonation with the same conditions as the base fuel. If the number is over 100 it indicates the mililiters of tetraethyl lead that is added to isoocatane to knock the same as the base fuel. It really isn't the most scientific scale ever created. I don't think though that just because there is a higher octane number that the fuel won't burn as efficiently though, but maybe I am wrong about that.

-Wes

[meZoom!]

i was so moved by this thread that i accidentally on purpose pumped in 89 instead of my usual 91 and see no difference, or actually kinda like it.

[nixx]

Originally posted by yamahito
My findings in short:

Lower octane detonates easier, if you put a higher octane it will not detonate as efficiently and may leave carbon deposit buildup in your engine (so actually using higher octane may be more 'dirty' for your engine).

Higher compression engines e.g. WRX are compressing the gas to the point where 87 octane may predetonate (remember, it detonates easier). This is the reason they need higher octane.

Bottom line is that higher octane in an RS will actually make it run less efficient and cause more buildup.

Replace 'detonate' with 'combustion' then now I agree 100%!

Plus why can't ppl take a look at their owners manual because it clearly says to put regular (87) for 2.5RS and premium (91-94) for WRX. If you're stock just go by those guidelines unless you have some engine management to advance the timing.