Running 99/ 100+ octane or E85 mixed with 93 on stock tune?

[Chandler]

I am going to the track Sunday. Is it safe to run 1:4 E85/93 or any 100+ octane fuel? Any negatives? I know the E85 wouldn't be problem with a tune, but will the stock ECU map adjust to it enough to be useful over 93?

[Jones2012s4]

It will adapt, it wont provide much, but rest assured you will be getting full timing advance, which will equate to the most power you can get out of the stock tune I would imagine.

I would save your money on the 100 octane and just put a 1:4 ratio of e85:93

On a stock tune that is more than enough to keep the timing advance high. Heck, on a stock tune, putting in 2 gallons of e85 should allow the car to run full timing. E85 is(in my book), the boost readily available, boost, friendly, cool running, fuel you can put in your car.

[jazza08]

25% might be a bit much for a stock tune? I'd go with a 10% mix to raise the octane level to avoid knocking and help with cooling. Anything more and the car begins to lean out because of the E85.

[Jones2012s4]

25% might be a bit much for a stock tune? I'd go with a 10% mix to raise the octane level to avoid knocking and help with cooling. Anything more and the car begins to lean out because of the E85.

False.

The car will not lean out. The car will add more fuel to make the AFR it is programmed for. If it can meet the AFR on a tune pushing 18lbs of boost, there is no problem meeting the desired AFR on a stock tune pushing 10lbs, with less timing.


I have run 50/50 60/40 70/30, and logged all of them, adding 25% e85 to the stock tune will not lean the car out.

Fact.

[AZT]

Jones2012s4, agree with you on leaning - so have you seen evidence that the stock program will take advantage of the mix (advance timing beyond even what it runs on 93)?

[jazza08]

Yes it can add fuel but the ecu has a max value it can add and if it exceeds this it will lean out. I don't know the max value hints why there was a question mark after what I said.. I also see zero benefit of using 25% on a stock tune? As little as 10% would raise the octane enough to allow him to use the maximum timing figures in the stock tune wouldn't you agree?

[s14roller]

I honestly don't see any reason to run over 93 oct on a stock car.

[jazza08]

I think he's just looking for some extra octane to ensure the engine doesn't knock or ecu retard ign timing so he gets maximum performance whilst on the track, a small amount of E85 will achieve that plus give some benefits in running cooler etc

[Jones2012s4]

I think he's just looking for some extra octane to ensure the engine doesn't knock or ecu retard ign timing so he gets maximum performance whilst on the track, a small amount of E85 will achieve that plus give some benefits in running cooler etc

This, 25% is overkill yes but the car will have no problem achieving the proper AFR.

10% and he should hit max timing with no ignition retard.

[Chandler]

This, 25% is overkill yes but the car will have no problem achieving the proper AFR.

10% and he should hit max timing with no ignition retard.

I filled up my car just yesterday with 93. I am not even at 3/4 a tank. I will drive 15 miles to top off with some E85 and then make the 200 Mile commute in the car to the track, giving the ECU PLENTY of time to adjust. I should be able to get E85 at the fuel pumps outside the track and mix it there/ fill up.

I have read some people's comments on Subaru forums and other places - even some regarding the S4. once you get much higher ratios (40-50% E85), the car runs to lean - but I don't understand that as the fuel is more oxygenated, correct? Oh well - I will run 10-25% since my mixing won't be perfect anyway. I doubt I will see much of a gain/ performance increase as I am well below the novice level when it comes to tracking.

Thanks guys!

[chaos2984]

Well honestly when the car is in closed loop it will adjust in like 5 miles or less. Honestly as soon as the engine goes in closed loop it will adjust instantly on the short term fuel trims and if if they get to high or low they transfer into long term and 0 out the short term. It doesn't take long to get the numbers into long therm where you want them.

But on the note of E85 YES you will run lean. People have to realize E 85 is like 120 octane or so. And what is octane they higher the point value the more it is able to resist knock. And the more its able to resist knock the harder it is to burn. So to compensate for that the car will jack up and have to add more volume of fuel to get the same burn. thats y cars that can run e85 have to have fuel maps and sensors and bigger injectors to be able to run e85. Ive seen it a lot in the dealership world with e85 cars with people running e85 and putting regular fuel in the tank and the car not adjusting correctly back to normal fuel and the ecm thinks it has e85 or some percentage over 20% of E in it and the fuel trims will be very negative and the car throws rich codes because normal fuel is more combustable than e85.

Just think of it like think regular gas is like dry wood and e85 is like wet wood. Dry wood is easier to burn than wet wood.

I would just put like 2 -3 gallons in max. Remember the car's ecm is set to run normal on 91.

[AZT]

But on the note of E85 YES you will run lean. People have to realize E 85 is like 120 octane or so. And what is octane they higher the point value the more it is able to resist knock. And the more its able to resist knock the harder it is to burn. So to compensate for that the car will jack up and have to add more volume of fuel to get the same burn. thats y cars that can run e85 have to have fuel maps and sensors and bigger injectors to be able to run e85. Ive seen it a lot in the dealership world with e85 cars with people running e85 and putting regular fuel in the tank and the car not adjusting correctly back to normal fuel and the ecm thinks it has e85 or some percentage over 20% of E in it and the fuel trims will be very negative and the car throws rich codes because normal fuel is more combustable than e85.

That explanation is not true. The reason ethanol runs lean has nothing to do with octane but rather it contains extra oxygen (like adding unmetered air) and less hydrocarbons (like taking away fuel) per unit than normal fuel. More air,less fuel = lean.

Just think of it like think regular gas is like dry wood and e85 is like wet wood. Dry wood is easier to burn than wet wood.

Maybe more like mixing a margarita with watered down tequila. Can't use the normal mix ratio and must add extra watered down tequila to bring things into balance lol.

[kap09]

Racetrack or drag strip? If racetrack is the answer, keep in mind that you'll take a huge hit in MPG with E85 in the mix. Could be an issue depending on how far to the track from the pump and how many time you plan on crossing start/finish.

[jazza08]

E85 is rated at 105 octane not 120 I believe?

[triz08]

I will have to test this out the next time I go to the track by mixing a small amount of 104 octane on my 93 tune. Very curious on the results.

[Chandler]

My car dropped just under a fourth of a tank by the time I found the shell station that offered E85. The one I thought had it stopped carrying it a few months ago. With that being said, I probably have about 27% E85 and drove about 10 miles back to the house, not aggressively. When I hit to road tomorrow I will top off with some 93 to help level it out :p

I will be doing 5 25 minute sessions, so I will have a few opportunities to get fuel across the street else I can pay the premium and buy what the track has to offer.

[chaos2984]

That explanation is not true. The reason ethanol runs lean has nothing to do with octane but rather it contains extra oxygen (like adding unmetered air) and less hydrocarbons (like taking away fuel) per unit than normal fuel. More air,less fuel = lean.



Maybe more like mixing a margarita with watered down tequila. Can't use the normal mix ratio and must add extra watered down tequila to bring things into balance lol.

ok sorry for the confusing but my over all explanation was right that it will run lean. Thats y the cost of E85 being cheap isn't really that cheap. Because you get like 25% less fuel mpg. And i was just guessing at the octane rating. Its not really listed because it doesn't matter except for what we want to do with it.

[Jones2012s4]

ok sorry for the confusing but my over all explanation was right that it will run lean. Thats y the cost of E85 being cheap isn't really that cheap. Because you get like 25% less fuel mpg. And i was just guessing at the octane rating. Its not really listed because it doesn't matter except for what we want to do with it.

The car will not run lean with 10% e85 in the gas tank. Nor 20, 30, 40, once you start getting around 50-60% then the fueling system can't compensate for the higher oxygenation of e85, meaning it can't pump the required amount of fuel to make the requested AFR.

This is why cars running full e85 require bigger injectors, higher flowing pumps, bigger lines, etc.

As far as our motors and fuel systems are concerned the car will not run lean until you start reaching around 50% e85 mixture.

I know this by testing, logging, repeating, not speculation.

[chaos2984]

The car will not run lean with 10% e85 in the gas tank. Nor 20, 30, 40, once you start getting around 50-60% then the fueling system can't compensate for the higher oxygenation of e85, meaning it can't pump the required amount of fuel to make the requested AFR.

This is why cars running full e85 require bigger injectors, higher flowing pumps, bigger lines, etc.

As far as our motors and fuel systems are concerned the car will not run lean until you start reaching around 50% e85 mixture.

I know this by testing, logging, repeating, not speculation.

Yes i know this. I posted that. most fuel around the country already is E10. Atleast its that way in my state. They outlawed MTBE over a big spill of MTBE.

But yea it will run lean as in leaner than normal with the 20 30 40% but where it makes a difference like you said is when the fuel tims cannot compenstate any more and maxes out. Then you get check engine light lol. But you can run whatever you want technically if the fuel trims can adjust correctly for it and not max out agains whatever % it maxes to to compensate for it Its usually +- 20 or 25%