I've done some searching on this forum and I can't seem to come up with a clear answer.

Is there any reason to use a mixture of "Cali" 91 octane with 100 octane if your Evo is stock?

Will the stock ECU adjust timing and A/F on it's own...without a reflash?

Does this mixture of octanes produce any horsepower gains?

 

In many cases, an Evo running on 91 octane pulls timing to keep bad things from happening to the motor. Upping the octane to 93-95 by mixing in some 100 octane is a good way to keep the ecu from feeling the need to pull timing. So yes, it does make a difference, if your only other choice is 91 octane.

SC~

 

more octane in an evo = huge power gains. But its not cheap. Use Xylene, for 10 dollars u get 1 gallon at home depot and u mix it in with a full tank to get near 93 octane or half a tank for near 100.

 

Just to clarify, the stock ECU will not try to take advantage of more than ~93 octane. You will need some kind of aftermarket tuning to see the big gains with higher octane gas.

 

Thanks for the input. So, the stock ECU will not adjust for higher than 93 octane. Therefore, a tank of 100 is just wasted cash?

 

I ran a tank of 100 octane Sunoco GT100 last October. I didn't notice any butt-dyno difference in the car. But when the tank got low, and I filled up with 93 octane Exxon, the car ran terribly for a few miles. The ECU, engine, etc., were strictly stock except for a Buschur axle-back exhaust.

I believe the stock ECU did "re-train" to the higher octane. I have no other explanation for why the car which had been running great on 93 octane for six months decided to act (at least for a few miles) like I was feeding it diesel fuel or something...

 

A 3:1 mix of cali 91 and 100 would be good (~94 octane). A full tank of 100 would be a big waste of cash.

IMO, of course.

 

no imho there's no reason to run 100oct unles you get a S-AFC, dynoflash, or something to lean out the A/F ratio (stock is like 9.1 so 100oct is a waste)

 

Race fuel allows you to run a tad leaner than normal... So you can up the boost a tad more with the higher octane without detonating.... It does help... Just buy 2 gallons of tolulene from Sherwin Williams and bump your car up to 21-22psi... 2 ways to lean your car out... tuning or upping the boost!!!