Hi!

I have heard for years that if you mix different levels of octane by, say, putting in a tank of 89 followed by a tank of 93, that you can get a combined octane level higher than 93. Is there any truth to this, or is it the automotive equivalent of an urban myth?

Thanks,

Chris Kennedy

 

i would think you could mix 1/2 89 and 1/2 93 to come up with some 91 octane.but achieving a higher octane than what you are using/mixing is not possible IMO.

 

BTW most 89 octane is already a blend.

 

yep i use to work for a stn and we use to have only tanks one for 87 and another for 93 so for a 89 its a blend fro 87 and 93, in case if we are out of 93 than 93 and 89 will be out of order, same with 87 if we are out than 93 will be available. Most gas stn's these days have 89 blend as it will cost another few bucks to dig 3 separate tanks.

 

No, youll get an octane in between the two ratings.

 

Nope; but if you do mix equal amounts of 89 and 93, you will likely get a resulting octane rating higher than 91.

 

I believe it works like this. I use this system for liquid dilutions.

RESULT OCTANE_DESIRED = DES
STARTING OCTANE1 = O1
STARTING OCTANE2 = O2

Parts Octane1 = ABS(O1-DES)
Parts Octane2 = ABS(O2-DES)

Total Parts = Parts Octane1 + Parts Octane2

Example1:
Want 92, have 93 and 89.

92 - 93 = 1, parts 89
92 - 89 = 3, parts 93

Total parts = 4.

1 gal 89 + 3 gal 93 = 4 gal 92


EXAMPLE2:

Have 4 gals 92. How much 100 oct to add to it to get 94?

94 - 100 = 6, parts 92
94 - 92 = 2, parts 100

If 4 gal = 6 parts, then the 100 oct = 2 parts, so:
4 gal 6 parts
----- = ------
x gal 2 parts

6x = 2 x 4, x = 4/3 gal 100 octane.

My head hurts now, someone check this...

 

I believe this legend is from back in the day when leaded regular was still available.

...back in High school I was told to mix regular leaded with unleaded premium to get lower cost high octane leaded fuel.

Supposedly the lead would increase the unleaded premiums octane and the unleaded package would help the anemic leaded


It seemed to work with my high compression 1960s and 1970 big blocks.

I couldn't afford race gas, no-one in the local area offered premium leaded and my cars pinged with the leaded regular.


Mike

 

In Europe we use 98 and you can even find 102 in germany.
I am running a 1991 completely stock.

The car is running great but do you think a tune up made for this octanes fuel would bring anything ?

 

My buddy just got turbo kit installed in his GTO.... very cool... extremely fast BTW. They installed sometype of custom Methanol Injection system so under WOT it injects methanol into the intake manfold. I'm guessing methanol either cools the A/F mixture or increases the octane rating.

Just some food for thought I guess,

DG

 

98 is like 93 in usa... The octane levels are calculated differently.

 

Why do you want to increase the octane rating? You won't see any more power if all you do is increase octane. You could run 100 octane or more on your car and not see 1 more horse power, in fact it would probably make less.

To take advantage of the higher octane rating there are other changes that have to be made.

To answer your question though; no, you won't see an increase in octane by mixing pump gas. Also, the relationship is not linear. 4 gallons of 89 and 4 gallons of 93 do not equal 8 gallons of 91.

If you want to add octane there are some paint additives that are fairly effective. Toluene and Xylene should be available at a local paint supply store. I'm not going to get into mixing it here, but do some research before you add either to a tank of gas. Chances are you don't need the extra octane anyway.

 

Thanks, everyone, for replying to my question---I have been doing some additional research, as well, and it does look like we can put this "myth" to rest. Once again, I appreciate the detailed and prompt replies.

Regards,
/s/ Chris Kennedy

 

Even though I use 93 I occasionally get some ping. I have checked everything, and the engine runs great otherwise. I also had an '87 Iroc which did the same thing, as well as an '81 Corvette 4-spd which did the same thing. It's something which comes and goes, and there is no "pattern". Anyway, it's obvious you could spend bundles of money and still not solve the problem.

/s/ Chris Kennedy

 

If the octane responded in a linear fashion to the amount of additives, those calculations would be correct. However, octane increasing additives have a curve of diminishing percentage improvements as more and more is added. Therefore if you mix 1 part of 89 octane with 1 part of 93 octane, you will in fact end up with a higher octane rating than 91.

 

Mike is correct. I used to do this because I needed the highest octane avail for a 10.5 :1 compression ratio. The added kicker was because I needed the lead for the valve seats. When the transition to all unleaded was in progress, you could get 91 octane premium unleaded but only 89 octane leaded. The lead additives were what kicked up the octane rating on the unleaded.

 

 

True. Back then, you could mix two different octanes together and the resulting brew would have a slightly higher rating than the highest of the original two. I saw an explanation in a national magazine, years ago.

But, not anymore.

Larry
code5coupe

__________
I ain't easily impressed....

 

If you could mix the two, and end up with a higher octane, the oil companies would do it, and then "water" it back down to the original octane!

 

I was always told to run the MINIMUM octane possible before your car starts pinging, if you're looking to pick up power. Octane rating is the resistance of the gas to explode. When you run an octane higher than is necessitated by your compression, the gas does not explode with as much force as the minimum octane will.

Personally, I run 91 in my 1985 because I don't want ANY risk of ANY pinging, because the car is old. I'm worried that any predetonation will damage the motor.

The only reason you'd need octane like 98 or 102 is if you're running really high compression, which generates heat (as a gas expands it cools, this is why an aresol can feels cold, and as a gas is compressed it gets warmer, like if you feel the valve of your bike tire after pumping it up) this heat causes the lower gas to detonate. Depending on the vehicle, this heat generated may or may not necessitate the use of premium gasoline.

If you have a high compression iron block, or an engine that is running some kind of forced air induction, you will generally need premium gas or more. (Beware of most octane boosters, they're usually snake oil).

Stock engines generally do not need super high octane, save some money for some mods that might make you need it!