Hey everyone,

Quick question regarding fuel for the Evo IX.

If anyone has seen my latest posts, I'm currently bringing my Evo IX out of long term storage and that leads to my inquiry.

As we all know, Mitsubishi recommends 93 octane fuel for proper operation and performance. Running 91 octane is not recommended but can still be done safely per the owners manual, although I've heard of numerous Evo owners reporting engine knock when using 91 octane.

Performance wise my Evo is completely stock with the only engine modifications being the addition of an Amsoil cone air filter utilizing a Vibrant MAF adapter plate and an AGP oil catch can.

I currently live in AZ and do not have any availability of 93 octane at local gas stations.

That being said, I have found numerous stations selling 100 octane unleaded fuel. Could I fill my tank with 7 gallons of 100 octane and 7 gallons of 91 octane resulting is a tank of 95.5 octane? A higher octane fuel is safer in many regards that a fuel which is too low octane so being 2.5 octane over the recommended level should be alright. Please correct me if I'm wrong.

Does mixing fuels of different octanes work? Would I technically have 95.5 octane fuel if each part of mixed fuel was an even amount?

Also, would there be any chance of engine or catalytic converter damage due to running the mix of fuels resulting in 95.5 octane? Any issues to be concerned with?

I'm currently stock with no plans of tuning for 91 octane or E85 as of this moment.

Any help would be greatly appreciated.

Jason

 

You'll be fine on 91. Why are you against getting a tune? It's the best mod you can do to the car. And ditch the stupid catalytic converter.

 

My car has lived on 91 octane all of it's life. But, yeah, you can mix fuel.

 

It's fine. It's not as if Evo owners in California are grenading their motors due to 91 octane.

 

Go get the car tuned. Proper timing and some more boost will really wake it up.

 

This

 

Thanks for all of the replies.

As of right now my main goal is to get the vehicle back out onto the road. A tune will definitely come later on but not right now.

My main focus is getting the correct fuel for my Evo. I do understand that I shouldn't have any issues with 91 octane but the idea of "making" 93 octane by mixing fuels intrigued me.

So, mixing 100 and 93 would be perfectly safe, correct? No cause for worry when it comes to the engine or catalytic converter?

 

From what I understand mixing fuels doesn't create a new octane rating in a sense people think... Race gas is made with different processes and different chemicals to get its octane rating than pump gas, but with that said people mix them all the time with no issue.

 

Echoing everyone above, 91 is just fine for your car. Absolutely no need to use 100 octane. But just as a friendly FYI, yes you can mix fuels, no it doesn't always result in the "predicted" final octane value based on ratios mixed, yes 100 octane will be fine with a cat, only leaded fuels will clog cats and damage sensors.

Get it tuned. You think you're being safer by running it stock but you're not. You've already changed your air filter which allows much more air to be taken in than is expected on the stock tune. You've altered a component of the combustion cycle without any compensation in fuel control. Will your motor blow up? No, because it isn't that drastic of a change and the ecu can compensate to some degree, but it won't be optimal. Long term storage is possibly the worst thing for a car. Shake the car down, get it tuned and run that SOB out. Get it hot and blow all the stagnant crap out of it.

I store my car through winter and frankly, hardly drive the poor thing in the spring and summer. But I make it a point that every time I drive it I get everything up to operating temp and bang it out to the rev limiter a few times. Worst thing for your car is for you to baby it. Get it back in shape, go easy until everything seems to be mechanically sound, then hit it hard.

 

It's a waste of money, if you don't need it and your only intention is to mix enough of it to essentially have a tank of 93. I used 100 octane once, but only because I accidentally put in 89 octane and didn't realize it until I was almost done filling up. And even then, the car was fine, though I knew to baby the car... but I still had to drive it around to make enough room for the proper amount of 100 octane I'd need to put in.

 

So you're a keep it standard guy like I was, but you now have a car fact tuned to 93, at the start that was me too but if I was you I'd run 91 to complete your exercise and take easy for one tank then I'd perform one upgrade exercise and that would be to wake it up and take advantage of your 100 oct, so I'd purchase a quiet 3 inch turbo back, a walbro, 1000 cc injectors and a 100 oct tune, either by shop or DIY, you can mothball your factory exhaust and parts and bring it back to standard anytime. You will now have a safe 50 HP extra rig to have fun with and trust me you'll wish you did this years ago, I'd also do the diff mod and other bump steer upgrade handling mods. These are all within standard guys range of common sense upgrades that can easily go back to stock to satisfy standard guys values cause I'm a standard guy too IMO

 

I don't think he's asking about how to best utilize 100 octane, as much as he is asking if it's necessary or beneficial to add some 100 octane to improve the overall octane of what's in his tank on a close-to-stock car.