My local gas station sells both 91 and 101 octane fuel. Is it safe for me the use the 101 octane on my stock tune? The only mods I have are the K&N Typhoon, downpipe and RRE stealth cat-back. Still running the stock cat.

I was thinking of mixing about 2 gallons of 101 octane and the remainder of 91 octane.

 

Wouldnt recommend that! (there are a few ECU parameters that can be changed to accommodate the higher octane. (I.e. timing advance, fuel delivery, boost)

Sure you could get away w/it but a proper tune w/the gas youre running is always the best bet

Recommend you get tuned on E85

 

It will be fine and the car doesn't know the octane so the only thing that will happen is your car will be less knock prone, which is a good thing. The only thing not recommended is running leaded fuels through the CAT.

 

^^^Better said than my explanation

But isnt it true that running higher OCT does nothing for performance as in WHP gain? Octanes main benefit is to reduce knock & allow the ECU to perform at the peak of that state of tune?

Instead of messing w/raising OCT, would rather see the OP run E85. He's in SoCal so avail is not an issue

 

Actually running higher octane will be very helpful. It's pretty common knowledge that the stock tune knocks a bunch, and relies heavily on the ECU's safety mechanisms to not die. This is mostly because of the terrible gas we have, so tuners will pull out timing from the stock map to make things happy and consistent. If you put higher octane gas with a stock rom the car will knock less and thus the ecu wont pull as much timing, and you will get more performance.

 

A stock tuned Evo picks up power on 100 octane fuel. They come from the factory tuned for much better fuel than what we have in the US, and especially better than the cali 91.. Run as much 100 as you want.

 

Higher octane, in and of itself, won't make additional power. Unless the car is knocking on 91oct then adding 100oct won't make any additional power. On the 2012+ GTR, where it has active ignition advance, the car will increase ignition timing until knock is reached and then back off so in this case running a higher octane fuel will make more power. In the case of the EVO I do not believe it has this capability.

 

It doesn't advance timing per se, but the stock timing and boost levels create a lot of knock, especially on ACN 91 fuel. So adding 100 octane will make more power as the ECU will be able to run the commanded timing in the ignition map instead of pulling timing due to knock.

 

letsgethisdone and biggiesacks are correct.

 

Thanks for the replies!

My intention is to mix about 3 gallons of 101 and the remainder 91 to achieve an average of ~93. I'll give it a shot and see how she runs just for kicks.

E85 is an option for me, but I'm hesitant to tune the ECU since I don't want to deal with any issues to pass SMOG. It was hard enough to pass with the aftermarket downpipe...

 

You could have the car retuned for 91 octane fuel. It won't create an issue passing smog.

 

You won't have any problem passing smog with E85. They aren't going to ask you what fuel your running, and your not going to volunteer it either. Otherwise E85 burns cleaner than gas, and all the emissions systems can handle it just fine. Just make sure your fuel system (and everything else for that matter) looks stocker then stock.

 

I said that...

 

I was clarifying that if the tune is stock, it is definitely knocking and pulling timing. Therefore, 100 octane will add power.

You may not have this issue on a stock Evo with the really goo 93 octane you have, but it's an issue on ACN91.

 

You were right on target from the beginning. Matched my limited understanding!

Most of ya'll are a level or 2 above me