Octane/Mixing Info Thread

[JustMe]

I'm guessing that there are a number of people on here who, with the recent availability of race fuels through Wicked CAS and Alex (Thanks guys!), may be interested in doing a bit of mixing. Myself being one of them, I think it might be helpful to get some information on here, such as what kind of octane we can/should/shouldn't run, and what, if any, adjustments need to be made, so that people can have a decent idea of what they're doing. So everyone throw in your .02 if you think it'll be helpful. If it draws enough interest, hopefully this may be deemed worthy to sticky here in the tech section.


Found this on carforums.net:

'Originally Posted by jeffdsm
MON, RON and (R+M)/2

RON = Research Octane
MON = Motor Octane
R+M/2 = The yellow decal at the pump. Everyday street driving octane.

MON is the octane that we are most concerned of. This is the octane that best simulates real full throttle racing. It is also the lowest octane value.

When searching for race fuels, RON can be very misleading. Since it is the highest of the 3 octane ratings, many fuel companies use this value to overrate their octane.

R+M/2, or the yellow pump decal is just the average of MON and RON.

For instance...

The Rebel 100 Octane is (R+M)/2 octane rating. This is what it actually is...
MON = 96 Octane
RON = 104 Octane
R+M/2 = (104+96)/2 = 100 Octane.

Can you see the problem if a race fuel company tries to sells this as 104 Unleaded and does not tell you what rating it's using?

VP sells a 100 Street Blaze that is a MON 96 Octane, R+M/2 100 octane.

Now when it comes to real race fuel, this is the reason why if you do not make substantial changes to the timing and fuel curve, that you will most likely LOSE HP by dumping in C-16.

C-16 = MON = 117 Octane
They don't even have a RON for this fuel. It would probably be 123 Octane, and the Yellow Decal, R+M/2, would be 120 Octane. It's a full 21 MON point increase in octane.

With that high of an octane rating, the flame speed will be so much slower. You must advance timing to offset that slower flame speed.

BOTTOM LINE : When purchasing race fuel, look for the MON octane rating, and if they use RON then downgrade the fuel'

A really nice octane chart here with downloadable spreadsheet:

http://www.gnttype.org/techarea/misc/Octanemix.html

[Ballistic Motorsports]

Rule one is that Higher octane does not make power by itself. Using higher octane without the need for it will actually decrease your power NOT increase it

[ill_eagle94]

However, a lot of newer ECUs can adapt to a higher octane, making more power.

[why?]

Rule one is that Higher octane does not make power by itself. Using higher octane without the need for it will actually decrease your power NOT increase it

when talking about octanes you won't normally see on the streets, absolutely, as JustMe mentioned, dumping in 117 ron will probably perform much worse if you don't tune for it.

[kidcrash603]

I used to compete in demolition derby, and 8 years ago I bought a custom engine/carb/distributor combo built to run on 87. 2 years into owning it, my builder advised me to mix 3 gallons of 87 with 2 gallons of 102, because he said that the quality of pump gas had gone down and the 102 would make up for it.

I don't know enough about fuels to know if that's right or not, but my engine ran perfectly for the 5 years I owned it, before selling it to a guy in Canada who is still using it.

Are there additives in "race fuel" that aren't in pump gas, that make it more desireable?

[Ballistic Motorsports]

ECU's are not adaptive in the way they will make more power than the fuel they were tuned for.

Most cars in the US are tuned for 91 max as 93 is not available everywhere in the country. This is why you see good gains from a tune on 93 because you are taking advantage of the higher octane. If the car corrected itself the gains would not be so great and you would have no need for a retune.

The Adaptive ECU makes corrections for airflow and temp mostly. And while monitoring the knock sensor will save your ass if you put 87 in a car requiring 91. Also remember there is Lead in race fuels above 100oct give or take a few blends that get up to 102-104. Lead is bad for O2 sensors and Catalytic converters. Also running a higher octane than required is just a waste of money. Higher Octane allows you to compress more air or bump timing without detonation. It does not create power on its own.


Now I am not trying to discourage people from buying the fuel. Buy all you want. I am just stating as has JustMe. Get the facts before assuming .So you are not wasting money on something not needed or harmful to your vehicle

[Ballistic Motorsports]

I used to compete in demolition derby, and 8 years ago I bought a custom engine/carb/distributor combo built to run on 87. 2 years into owning it, my builder advised me to mix 3 gallons of 87 with 2 gallons of 102, because he said that the quality of pump gas had gone down and the 102 would make up for it.

I don't know enough about fuels to know if that's right or not, but my engine ran perfectly for the 5 years I owned it, before selling it to a guy in Canada who is still using it.

Are there additives in "race fuel" that aren't in pump gas, that make it more desireable?

You had a motor built for a demolition car? Trying to follow here But either way. If you built it for 87 why not just run 91-93 instead if needed. Why mix the lowest grade with race fuel. Does not make sense. I do not doubt the car ran fine , no reason it shoudn't. You can take advantage of the fuel because you could manually advance the timing. But I bet that mix was over kill on a low compression motor.

But he is correct in that pump gas can have many different forms and is not as consistent as race fuel per mix .One of the reasons race fuel cost much more is consistency in quality. They also make different blends for different applications.

[OVRBST]

Forced induction cars since the early 90's rely on knock sensors as much as any other sensor in the car.

To give you an example. A Supra computer was designed to run on 91 octane but full timing is 23 degrees.23 degrees is not attainable with pump gas. What the computer does is push timing until the knock sensors say that's enough, then it puts that value into a long term memory for use the next time you go WOT. It will sample the knock sensor for feedback info, but knows that say 15 degrees is as far as it can go.
Add in 117 octane fuel. Now the computer will see the knock sensors are not picking anything up and continue to push the timing up until it maxes at 23 degrees.

In this case putting higher octane fuel in your car will make a dramatic difference. JoshS logged his stock computer to see all of this first hand. He went from 114 trap to 121.

Most FI cars can expect to see gains with 100 unleaded on the stock computer.
Most NA cars can expect to loose power.

[Intervention]

This is 87/93 octane chart on a bone stock 2011 Mustang...

The engine is tuned for both 87 and 91, and like the supra will adapt to either octanes and run more timing. Will it run a few more degrees if it has 100 octane, or is it maxxed out timing wise. I'm not overly sure

[Ballistic Motorsports]

Forced induction cars since the early 90's rely on knock sensors as much as any other sensor in the car.

To give you an example. A Supra computer was designed to run on 91 octane but full timing is 23 degrees.23 degrees is not attainable with pump gas. What the computer does is push timing until the knock sensors say that's enough, then it puts that value into a long term memory for use the next time you go WOT. It will sample the knock sensor for feedback info, but knows that say 15 degrees is as far as it can go.
Add in 117 octane fuel. Now the computer will see the knock sensors are not picking anything up and continue to push the timing up until it maxes at 23 degrees.

In this case putting higher octane fuel in your car will make a dramatic difference. JoshS logged his stock computer to see all of this first hand. He went from 114 trap to 121.

Most FI cars can expect to see gains with 100 unleaded on the stock computer.
Most NA cars can expect to loose power.

Interesting, I have not seen this, but I have not tried it with a Supra either. It is a Black sheep amongst others I guess. General consensus says otherwise. But also what I said above still holds true to what you are saying only that I was not aware the Supra had timing tables that high that it can take advantage of it. Other advantage I could see is if the car was heat soaked. I would be interested to see the IAT temps of both runs as well as coolant temp But again you know the Supra better than I I would be interested to see the sample rate and speed the Toyota ECU reacts to timing as we did tests for the AEM EMS and J&S safeguard. Giles helped John with the testing and software of the J&S and I know you can use it in the way the supra is controlling timing. Not everyone on the forum is driving Supras

We should test this theory of most FI cars. I would be interested in the results. But it would have to be unmodded cars to make it a fair assumption. I will throw down a $100 for fuel for the tests. I bet most other forums would like to see the results as I know they have this same debate on the North American GTR owners forum and the Subbie forums as well .Could be interesting as I like to challenge what has been the general consensus has been for years .

So Alex . Race fuel aside. Say we took a Stock supra base lined it and then tuned it for 93 without changing boost pressure would you see any gains? Other than correct AFR for gain you are saying the ignition maps are already optimized? Not arguing just interested in learning more 

[ill_eagle94]

People have seen results in many modern cars. Mazdaspeed3 owners have seen gains as well when mixing in higer octane rated fuel than you can get at the average gas station.

[OVRBST]

That's the factory ECU, AEM, Haltech, etc all get open loop tuned and maxed on whatever fuels the owner wants to run. I (and most other tuners) dont tune the car over aggressive and let the knock sensors pull timing becuase that puts a lot of responibility on the knock sensors. If they fail....so does your motor.

But to answer your question, yes. The OEM Supra computer is tuned 100% to the max timing possible on its own. AFR's need tweaking......lots of it. They like to run in the 10's so there's always some power left to tune out.

There are a few other cars out there that do the same thing also, but like you said, most NA and some FI cars wont pick up power with octane. Evo's and STI's are factory tuned not to knock. That means you dump 110 in the tank it will loose power because it won't push the timing up.