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Octane 87 v. 93

3373 Views 27 Replies 14 Participants Last post by  Icepuck72, 
F
Just got a '04 4x4 Tacoma, V-6 Auto and I was wondering if it really makes a difference on which octane I use. I'm talking about long-term, as well as short-term performance (which I know should be ever-so-slightly higher with the 93). I already ran about 4 tanks of 93 thru and want to make the decision now whether to stay with 93 forever, change over to 87 forever or alternate on some kind of basis. Thanks.
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drabnor
FortPieToyo said:
Just got a '04 4x4 Tacoma, V-6 Auto and I was wondering if it really makes a difference on which octane I use. I'm talking about long-term, as well as short-term performance (which I know should be ever-so-slightly higher with the 93). I already ran about 4 tanks of 93 thru and want to make the decision now whether to stay with 93 forever, change over to 87 forever or alternate on some kind of basis. Thanks.
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unless you have a supercharger, or are pinging, run the 87
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Mez
Every car Ive had always runs better on higher octane. You can just feel it :), especially running leaded 110 octane at 27psi in my car ;) .
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BigBadBob0
On a normally timed, normally aspirated 3.4l performance is actually lower with 93 vs. 87. Run 87. It's better for your truck and your pocket book.
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F
Thanks! I really appreciate the advice (maybe the supercharger-related comments will apply in the near future!)
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03trdblack
BigBadBob0 said:
On a normally timed, normally aspirated 3.4l performance is actually lower with 93 vs. 87. Run 87. It's better for your truck and your pocket book.
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You know what's funny though, the 2003 Factory Service Manual for the Tacoma says they did all their engine testing with 91 Octane fuel. This was also the fuel they used to post the horsepower/torque ratings from the factory. It really made me wonder why they would do testing with the higher octane and then recommend the lower octane rating....
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KRYPTO(dale)
in my daily driver,regular.

in the wheeler,premium-because i think it helps.
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Tankota
:banghead: Unless you are running a higher compression engine or the mfg requires it, you will get more power out of using the correct octane.. Most people have it backwords thanks to brainwashing by gas companies trying to make more money.. Higher octane gas burns more slowly than lower octane - Higher octane by itself will not give you more power in an engine that only requires 87, it's going to burn slower in those engines and have less power. The correct lower octane will burn faster and give you more power. the only reason to run higher octane is if the engine pings on the lower due to the gas igniting too soon - if you havn't put a supercharger or turbo or something else to modify the engine, and it still pings on the spec'd octane, then there is something else wrong with your egine, like carbon build up, timing, etc. In fact if you run a high octane fuel in an engine built for lower octane you will increase the carbon and junk build up becasue the engine isn't burning the fuel fast enough to burn it all. Modern computer controled engines can compensate a bit, but you will still get more carbon, etc.. One of the myths is that people run high octane in a low octane engine for a long time, then one day they try switching back and either lose power or ping - and say the engine runs better on the high octane they have been using.. this is from either the computer not having time to recalibrate the timing to the faster burning gas, or the carbon build up and heat from running the high octane, or both..

Bottom line is - if it's spec'd for 87, run 87. you will get the most power, cleanest burn, less build up and deposits, and lowest emmsions. Only run higher octane if you need to due to engine design or high performance modifications. Otherwise you are just tossing free money to the gas companies, and may in the long run be harming the engine..

Everybody can feel free to paypal me the extra money they waste on unneeded high octane gas instead, I'll put it to better use than the stupid gas companies.. [email protected] :D
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F
That's the kind of answer I would expect from the wisdom of the TTORA website. My brother tuned me in to this website/forum and the amount of expertise & knowledge that I have gleaned from it is astounding. I really appreciate it and hope that someday I can offer such good advice. Thanks!
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S
You can always split the difference and run 89.
I've been running 89 in my Tacoma trucks for yrs. According to the butt dyno I seems to get a better running engine with the 89 vs the 87.
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BigBadBob0
In case you were wondering, David, you're 100% right :) I had hoped that my mini version of your post would get that point across.
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Tankota
BigBadBob0 said:
In case you were wondering, David, you're 100% right :) I had hoped that my mini version of your post would get that point across.
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I get a little long winded sometimes and get carried away.. lol.. Gas / oil companies and Bank of America are two of my pet peeve companies.. :p
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N
03trdblack said:
You know what's funny though, the 2003 Factory Service Manual for the Tacoma says they did all their engine testing with 91 Octane fuel. This was also the fuel they used to post the horsepower/torque ratings from the factory. It really made me wonder why they would do testing with the higher octane and then recommend the lower octane rating....
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Actually in the manual they say 91 research octane number (RON), whereas on the pump they only give you the average octane number (R+M/2). Reportedly, sensitivity is almost as important as average octane number, but see if you can find that on any pump!!!
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G
Probably because they advance timing so much they would get detonation if they didnt run 91. They would advance timing to increase power output.
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GoodyearMTR said:
Probably because they advance timing so much they would get detonation if they didnt run 91. They would advance timing to increase power output.
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I think you missed the point, they say 91RON, this is not the same measurement as they quote on the pump when you go to fill up. The 91 is not the "octane" of the gas that everyone knows about.
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F
GoodyearMTR said:
Probably because they advance timing so much they would get detonation if they didnt run 91. They would advance timing to increase power output.
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What everyone else said. They can't get away with running 91 octane for the testing and then recommending 87. The 91 listed in that manual is research octane number, the "R" in (R+M)/2. The "M" is motor octane number, which is a lower number. R and M are averaged for the octane that is posted on gasoline pumps are required by federal regulation.

A fuel with a RON of 91 and a MON of 83 is 87 octane.
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T
I don't doubt what you guys are saying about higher octane fuel burning slower. I also believe that if the timing were locked down and fixed and there was no detonation, 87 would perform better than 93. However, the timing in our vehicles is not fixed. In doing all the mods to my truck, I noticed that the knock sensors are more sensitive than my ears. Even when my truck was normally asperated my scan tool showed that the knock sensors caused the ECU to pull timing even though I never heard any detonation. I switched to 91 octane and timing was retarded much less often. I can't remember where I read it but remember some "expert" saying for every degree of timing pulled meant a loss of 12 HP at WOT. I can't remember if that was NA or with the S/C. If you look at my dyno run sheet from the webshots link in my sig, you will see at 4700 RPM the knock sensor caused the ECU to pull timing. We never heard any detonation. Look at the momentary drop in HP and torque at that point. The ECU pulled timing even though I have fuel mods, water injection, and was running AFR's at 12.1 to 12.5.

Bottom line is, if I went back to an NA engine, I would probably still run higher octane fuel to make sure timing stays optimal. I can't hear all the knock sensors pick up. The less timing the ECU pulls, the more power my engine makes. I feel less retard more than makes up for the loss of performance using slower burning fuels. IMHO.

Dave
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TRDOLMAN said:
If you look at my dyno run sheet from the webshots link in my sig, you will see at 4700 RPM the knock sensor caused the ECU to pull timing. We never heard any detonation. Look at the momentary drop in HP and torque at that point. The ECU pulled timing even though I have fuel mods, water injection, and was running AFR's at 12.1 to 12.5.
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I dunno about that. If your ECU retarded the timing at 4700 rpm then what made it instantly jump up 20 hp by 4800 rpm?
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T
flatlandtacoma said:
I dunno about that. If your ECU retarded the timing at 4700 rpm then what made it instantly jump up 20 hp by 4800 rpm?
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What I was told by the "experts" is that, contrary to what I thought, the ECU will try and add timing back instantly and apparently that's what it did at 4800 RPM. I always thought that once the ECU pulled timing, it took a long time to advance again once the knock sensor settled down. I guess the "experts" were right and I was wrong. I am still trying to learn about these things. This is my first time trying to mod a computer controlled engine.

Dave
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TRDOLMAN said:
What I was told by the "experts" is that, contrary to what I thought, the ECU will try and add timing back instantly and apparently that's what it did at 4800 RPM. I always thought that once the ECU pulled timing, it took a long time to advance again once the knock sensor settled down. I guess the "experts" were right and I was wrong. I am still trying to learn about these things. This is my first time trying to mod a computer controlled engine.

Dave
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Bah, I'm still skeptical. The ECU does start adding back timing as soon as the knock disappears, but it is supposed to be a more gradual slope than it took it away by. I don't see that at all on your dyno sheet. There are more sensors than just the knock sensor that will advance or retard your timing, if that is even what is going on there.

Check out this link, it is a good read from some Toyota technician training on the subject:
http://www.autoshop101.com/forms/h40.pdf
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