So I filled my tank with 100 octane gas, and I was just wondering how long the ECU generally takes to figure out it can switch to the high-octane map? I was running 92 octane up until now.

 

AFAIK, the ECU will always attempt to run the default WOT spark curve until or unless it detects knock. I don't know the specifics of the default curve or to what degree of an advantage (if any) it allows for running higher octane fuel.

 

IIRC, Shiv posted a while back that it can, in some cases, take as long as several days.

He also told me that when the battery is disconnected, the ECU has to "re-learn" the idle. If this is the case, maybe disconnecting the battery will also set the ECU to it's default (more aggressive) map.

BTW, from what I've read here, there is no additional benefit beyond 93 or 94 octane in a stock EVO. Unless the car is tuned for 100 octane, you are just wasting money. 93 octane should be knock-resistant enough for the ECU to run the aggressive map and not pull timing.

Can someone please correct me if I'm wrong.

 

I'd also like to comment that, even with Unocal 76 91 octane, the ECU still seems to pull timing from time to time.

I thought I had noticed a tendency to pull timing less often with the 76, but after several tank fulls of it, I found it to perform similar to other brands.

I am currently using Shell 91 and it seems to be working well.

Dammit, why can't we get 93 octane here in SoCal (for the price of 91 or a little higher)?

 

the stock ECU will never add enough timing on its own to make 100 oct fuel benificial enough to justify $4+ a gal

 

If we could rig up our cars to run on E85 (85% Ethanol, 15% Unleaded) we could enjoy over 100 octane for less than the price of regular

 

There's a thread about it here:

https://www.evolutionm.net/forums/sh...&highlight=e85

Does anybody have any further information? E85 is available at pumps near my house and 93 is up over 2.60/gal.

d

 

It's complicated to rig your fuel delivery and electronics to run alcohol, but it can be done. Lots of dragster guys love running alcohol. it burns cooler & has higher octane than gasoline.

 

My understanding is that the e85 mix doesn't require modifications of the fuel system, 02 sensors, cats, or compression characteristics. There's a long list of regular, CARB compliant, cars that are already certified from chrysler.

d

 

And it burns at twice the rate of gasoline, and has almost twice the weight of gasoline. That's why we run alcohol at the track only. I learned alot about alcohol as a fuel while working with a dirt sprint car team years ago.