I live in So cali and settle for our crap 91. I'm getting a S-AFC and tuning a map to run on 100 octane on weekends and track days. Then..I'm using the crap 91 the rest of the time.
my question is...are there any down sides to this? Engine damage?
And is it ok to top off with 100 octane while still having half a tank of 91?

thanks for help

 

wondering this also,but i have a dynoflash set with 91 oct.

 

No problems at all that I know of. I would not run your 100 oct map until you know there is only 100 oct gas in the tank. Since your running 100oct I'm sure you will be turning up your boost so make sure you get head studs sooner or later. I have run 100 with boost turned up and no map this I would not sugg. but that's not you.

 

i also have a dynoflash for 91 octane.
just found out a nearby gas station has 100 octane.
anyone else have comment?

 

I cant belive you put that **** in your car

 

on a stock or lightly modded (read no ECU work) will a 50/50 mix of 91 and 100 octane help or hurt?

 

any higher octane will always help a car, if not for anything but safety...

To the original poster: If I'm not mistaken, the S-AFCs can have 2 maps, tune one for 100 and one for 91... If I am mistaken, then simply unplug the S-AFC when you're not on 100 octane and let the stock ECU do all the work. It is okay to top off like that, but do not assume that you have 100 octane in your tank untill you've filled up the entire tank with 100 octane... in other words, run a few laps till the gas light is on, THEN fill up with 100 octane and plug your S-AFC w/ 100 octane map in.
IF you tune for 100 octane and leave the S-AFC in with the 100 Octane map and fill up with 91 octane there will almost definitly be consequences, how severe the consequences will be is hard to say.

For those that have a 91 octane dynoflash or something and switch to 100 octane fuel, usually cranking up the boost 1-3 pounds is perfectly okay for the car, I had a local shop that tunes really conservative on all cars (they recommended I run at 19 pounds of boost on my 91 octane) tell me that turning it up to 22lbs would be just fine on 100 octane and is what I've done at multiple track events.

 

Help.

 

My understanding is that the evo is tuned for 93 octane gas. We also only have the 91 octane premium in Nebraska, but Sunoco GT100 is available at several stations here in Lincoln. I asked a station about it, and they told me that in a 14 gallon tank, 4 gallons of the GT100 and 10 gallons of 91 octane would get me to 93 octane.

Has anyone tried this?

 

I'm Gonna Get Some Of That Gt100 This Weekend There Is A Gas Station In Leominster Mass That Has It 5 Gallon Drum For $43.00.. Gonna Mix With 93octane

 

Isn't 43 bucks for 5 gallons of 100 octane a rip off? That's like 8 bucks a gallon... it's 5 bucks a gallon everywhere I've been.

 

If you want to mix 91 & 100 octanes, here are the ratios for particular octane levels you are trying to achieve:

 

I live in the middle of an oilfield with a refinery 20 miles away and the best gas I can get is 91 octane.

 

Thanks for the Chart! Exactly what I was looking for!

 

Nope! The EVO can store multiple maps for different types of Gasoline all the way from 96 Octane to 91-90 Octane (actually its more of a dynamic map). So in stock form anything more than 96 Oct. will not make more power. But nothing lower than 91-90 Oct. is recommended. Several of us EVO owners in Nebraska use BP 92 Oct. gas. No need to mix but you can mix with the 100 Oct. to bump up your Oct. levels and thus make more power.