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Old 10-16-2009, 09:05 AM   #1
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A little talk about OCTANE

Often people refer to high octane gas as though it has some properties that it, in truth, does not. I thought it might be educational to make a thread about this and see where it leads.

Myth 1) High octane gas will make more power.

Octane rating is a measure of a fuels resistance to detonation. Nothing more.
This myth stems from the fact that a higher octane rated fuel, when used in a high performance engine, will allow higher compression ratios to be used without detonantion. High octane SLOWS gasolines rate of combustion.
That means it produces less power than lower octane fuels, when used in engines not requiring it's use.

Myth 2) High Octane gas is better quality than regular gas.

The octane rating of gasoline is modified by the addition of different chemicals with long fancy names. These chemicals help combustion but do not enhance the base gasolines quality otherwise.

Myth 3) High octane gas will clean your engine.

There may be additives in high octane gas that help clean deposits like minor carbon buildup and there may not. These additives are not a function of octane rating.
Of course, some motorcycle engines are fairly high compression and require the use of increased octane rated fuel but, if your carbs are dirty it will take more than spending extra money at the pump to fix them.


Much of the confusion surrounding high octane gasoline comes from the late 1960's when high performance cars became popular. The muscle car era brought large displacement, high compression engines that needed higher octane rated fuel than cars from previous years.
The oil companies capitalized on the new popularity of performance cars by advertising "Premium" and "Super Premium" gas. Just like hair care products are attributed with elusive properties like brilliance clarifiers and luxurient moisturizing, the oil companies gave high octane gas special properties too.
It was advertising hype that eventually moved into common speech. It is now used as a way of intensifying descriptions. For example movie reviews talk about "high octane excitement".
So here we are 40 years later and all these myths still swirl around the term and people keep repeating them like viral videos get passed around the internet.



From Wikipedia:

The octane rating is a measure of the resistance of gasoline and other fuels to detonation (engine knocking) in spark-ignition internal combustion engines. High-performance engines typically have higher compression ratios and are therefore more prone to detonation, so they require higher octane fuel. A lower-performance engine will not generally perform better with high-octane fuel, since the compression ratio is fixed by the engine design.
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Last edited by bumblebee; 10-16-2009 at 09:08 AM.
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Old 10-16-2009, 09:18 AM   #2
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even if you do have a higher compression engine, the only way you are really going to benefit from higher octane fuel, is advancing timing accordingly.
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Old 10-16-2009, 09:25 AM   #3
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Quote:
Originally Posted by chase View Post
even if you do have a higher compression engine, the only way you are really going to benefit from higher octane fuel, is advancing timing accordingly.
not if your compression is high enough to knock on lower octane
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Old 10-16-2009, 09:30 AM   #4
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Quote:
Originally Posted by didimao0072000 View Post
not if your compression is high enough to knock on lower octane
Bingo. A 10:1 compression engine might diesel (which means to ignite without spark) on 87 octane gas. NOT GOOD. This is how you break motors.
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Old 10-16-2009, 09:33 AM   #5
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So when in the owners manual says you can only add gas above 91 octane, is that BS?
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Old 10-16-2009, 09:36 AM   #6
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Quote:
Originally Posted by didimao0072000 View Post
not if your compression is high enough to knock on lower octane
if ur compression was THAT high, you would know you have to run higher octane

I was referring to engines with slightly higher compression, that will still run fine with 87
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Old 10-16-2009, 09:43 AM   #7
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Quote:
Originally Posted by Irak View Post
So when in the owners manual says you can only add gas above 91 octane, is that BS?
it's not bs. 91 octane will benefit that engine. i assume your engine is fairly modern so putting in low octane will cause your engine to timing and you will lose power..
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Old 10-16-2009, 10:23 AM   #8
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Quote:
Originally Posted by didimao0072000 View Post
it's not bs. 91 octane will benefit that engine. i assume your engine is fairly modern so putting in low octane will cause your engine to timing and you will lose power..
Not necessarily true,my 07 GSXR1000 dynoed highest on 87 octane.You want it to burn as hot as possible without detonation
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Old 10-16-2009, 10:41 AM   #9
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Quote:
Originally Posted by mathews View Post
Not necessarily true,my 07 GSXR1000 dynoed highest on 87 octane.You want it to burn as hot as possible without detonation
motorcycle engines are different. their much higher rpms allow them to run lower octane because detonation has less time to occur..

oh yeah, in response to the 91 octane question, i was assuming it was for a car...
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Old 10-16-2009, 10:56 AM   #10
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Quote:
Originally Posted by didimao0072000 View Post
motorcycle engines are different. their much higher rpms allow them to run lower octane because detonation has less time to occur..

oh yeah, in response to the 91 octane question, i was assuming it was for a car...
I think there is still plenty of time for it to occur.
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Old 10-16-2009, 11:26 AM   #11
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Quote:
Originally Posted by Irak View Post
So when in the owners manual says you can only add gas above 91 octane, is that BS?
No, If the car manual states 91 octane you should use it. Otherwise you may be risking detonation and possible motor damage.

I think the OP's point is that if your car/bike whatever calls for RUG (87) then you are not really going to see any benefit in ruining premium 91 or 93. This is quite true.

On the other hand if you have a higher performance engine that requires a higher octane fuel you defiantly should use it (whatever the manual requires).

For example: In my case I drive an 06 VW GLI which is a 2.0 turbo motor. It requires 91 from the factory so I would never run it below that. I also have an APR performance tune that increases the timing and boost pressure of the ECU programming. The performance ECU tune that I run is a 93 or > tune so I am required to run 93 to prevent detonation. If I can't find 93 where I am I can switch down to a 91 program still more advance and higher boost than stock but less than the 93 program. Or if going to the track or for fun I can switch to a 100 octane ECU program for more power and run 100 fuel.

Long story short run the grade fuel the car/bike requires, no need to run a higher octane unless the modifications to the motor (compression, timing, boost) require it.
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Old 10-16-2009, 11:26 AM   #12
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Quote:
Originally Posted by bluewave18 View Post
I think there is still plenty of time for it to occur.
I haven't researched this but I'm gonna have to agree. If there is time for the fuel to burn, there is time for it to explode (detonate).
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Old 10-16-2009, 11:27 AM   #13
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Quote:
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I think there is still plenty of time for it to occur.
There is MOST definitely time for detonation to occur.
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Old 10-16-2009, 11:33 AM   #14
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Quote:
Originally Posted by SBAtdijetta View Post
Long story short run the grade fuel the car/bike requires, no need to run a higher octane unless the modifications to the motor (compression, timing, boost) require it.
Yep.

In fact in the late 80's a friend had a car that only required 87 octane but she always used "premium". After several years she had major engine problems (she was unable to adequately describe the problem to me).
The car was towed to Strickland Chevrolet in Pearland. The service manager told her that the extra additives in premium gas had caused deposits to build up in the engine. It was toast and had to be replaced.

I can't say if she got scammed or if the Serv Mgr was telling the truth but, it seems possible.
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Old 10-16-2009, 11:35 AM   #15
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Hmmmm.... thanks for the info. I was one of those with the 40 year old knowledge. Guess i'll stop throwing money away at the pump

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Old 10-16-2009, 11:35 AM   #16
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i run 87 in the bike, its cheaper. /thread.
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Old 10-16-2009, 11:41 AM   #17
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I was asking because almost all my vehicles state that, per instance the A4; the R6 and the WR250X state in the owners manual that you should use above 91 octane gas.
In Mexico when I had my 06 CBR600RR the manual said the same, I ran 87 octane and the bike worked really good, in fact as someone said it felt better than using 91.
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Old 10-16-2009, 11:46 AM   #18
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Quote:
Originally Posted by Irak View Post
So when in the owners manual says you can only add gas above 91 octane, is that BS?
Everyone pretty much covered it - use what's recommended, not bs. Now, if your manual says 87 and someone tells you it will do better with 91/93, that's BS. Essentially, whatever the manual says is what it's tuned and designed for until you alter something major.

Quote:
Originally Posted by didimao0072000 View Post
it's not bs. 91 octane will benefit that engine. i assume your engine is fairly modern so putting in low octane will cause your engine to timing and you will lose power..
Yeah, I think most (if not all) newer cars can tell when you cheap out on gas and lower the performance of a car. If the computer doesn't understand that you're using a lower octane fuel, you risk detonation.

Quote:
Originally Posted by mathews View Post
Not necessarily true,my 07 GSXR1000 dynoed highest on 87 octane.You want it to burn as hot as possible without detonation
Reread OP. It specifically states that a lower octane gas burns faster, and thus, will create more power in the same engine than a higher octane would (assuming the computer doesn't /advance timing at all). However, you run a risk of detonation using a gas the engine isn't tuned for. And I don't know about you, but that's especially not worth it on a bike where I'm basically curled up around the engine.
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Old 10-16-2009, 11:48 AM   #19
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I'm just gonna start running nitromethane in my bike...can't hurt, right?
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Old 10-16-2009, 11:51 AM   #20
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I did a little more poking around and found that it could be true that high octane gas may pose some risk for lower performance engines.
It turns out that the higher the octane number, the more heavy hydrocarbons are present in the gas. The heavy hydrocarbons can form "gum" deposits in the intake, intake valves and cylinder walls. If these deposits form on the surface of sensors used by the fuel injection system to control fuel/air mixture they can cause the engine to run lean. That could lead to detonation and bent rods, etc.
The gum deposits in the cylinder can lead to "hot spots" which can disrupt smooth combustion, also leading to detonation.

This is less of a problem now because of new additives to prevent the gum deposits, but it could still happen. A high performance engine that requires high octane fuel doesn't suffer as much from these deposits.
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