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mkarns

Minimum Octane

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Hi All,

 

I was just reading the owners manual for my recently purchased '87 GL Turbo wagon.

 

It says to use 90 octane.

 

I've been using 87 octane for a month now and it seems to be running fine, no knocking, hesitation etc, and I'm averaging 25 to 26 mpg.

 

Should I go to the 90 octane or not?

 

Thanks,

 

M Karns

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If the owners manual say 90, I would go with 90( or above).. Personally, whenever I run less than 91( no 90 here) The car feels sluggish and gross.. I run 93 all the time.. I get the best performance from it that way.. Almost every car I have had over the past 10 years has been turbocharged and I don't recommend 87 for ANY turbo car..

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just a word of caution, unless you have the anti knock requirements, ie; the manual says use XX octane, use 87, it dosn't help the engine to use a higher octane, it infact reduces power, unless you advance the timing it won't do a dang bit of good. on a turbo engine, absolutely use 90 but on an 83 hatchback for instance you don't really need anything above 87.

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I'll back Noah on that one - techically speaking lower octane fuels burn hotter and more completely. You can look this up in any automotive theory book. I also agree that the turbo engines should use the higher octane due to the boost levels which do not kick in till the turbo spools..... it may run fine at idle, but it won't when that boost kicks in.

 

GD

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Moreover, our owner's manuals refer only to Research Method (RON) ratings.

 

Here in the USA, we rate gasoline by (R+M)/2 which is the average of the figures achieved by the Research and Motor Methods. The Research Method usually results in a higher number than the Motor Method, so the 90 octane recommended in our owner's manuals actually equates roughly to our 87 octane gas.

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Noah, that's an interesting factoid. Do you work in the petroleum industry, or are you boning up for Super Millionaire? :D

 

Honestly, I didn't know that the research method trended higher - I just assumed they were closely related and the averaging was to correct for anomalies in the testing processes, kind of like the Bowl Championship Series computer average (oh wait, that doesn't work worth a dang!).

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Research octane is measured at a lower RPM with colder intake air, the Motor octane is measured at a higher speed and temperature, which more accurately resembles a real engine.

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Hmmm,

I have never been able to run any of my subarus on 87 octane without them pinging.

I usually run 89 but will tank up on 92 for long freeway runs or hot days.

That's been my experience......

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Run 93 or closest to it at ALL TIMES in a turbo SUBARU.

 

Non turbos, thats fine to run whatever...but id still run 93, cuz i mod it!:D

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I'm gonna have to jump in and say that if the motor is stock then run what the factory reccomends, I would tend to agree with those that designed and tested the car over hearsay and personal beliefs. however, if its modded, run what you need to keep her from pinging.

 

RussHill, if yours is pinging, try seafoam or top engine cleaner, that should get rid of some of the carbon in the cylinders and intake and return the inside of your motor to more 87 friendly territory.

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yeah, my brat pings a little on 87 but did better on 89. have yet to try premium. premium should cost what regular costs now! it's horrible.

i have a fresh tune up in there including 8mm wires. i'm tempted to buy an accel coil tomorrow but i shouldn't. shoulder angel says no, be good; shoulder devil reminds me that my income tax return deposited to checking today. damn that devil! :D

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In the spirit of peer pressure.. do it andy.. do it.. you know you want to.. everyone will like you if you do it.. you want to be liked don't you?

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I worked one summer at an oil refinery, and spent a lot of time with the tech that was in charge of octane testing. He used to test the gasoline sold by the competitors, as well as the gas produced in that refinery.

 

Some brands of gas had a huge difference between research and motor octane, even though they all averaged out about the same.

 

I was riding my Yamaha SR500, 1/2 liter single cylinder motor bike, which was really octane sensitive. It liked premium, but I could run it on regular if it had high motor octane numbers.

 

So, the bottom line is the (R+M)/2 number doesn't necessarily tell you what you really want to know about the fuel. Experimental results may be more valid than the number on the pump.

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I agree the higher the better I have switched back and forth:

 

87oct every time if I boost over 4 psi it pings, det, loss of power. but not boosting it does ok. but that one time you really want to go you are screwed, ping ping ping, pi, pi PING!!

 

91oct for the most part pretty good for me, before I was having some injector problems and it would ping on this too. got new injectors now everything a ok.

 

never really tried the one in the middle. My manual doesn't give any specs on recommended oct rating. Its an 86.

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