You can't really speak in generalities when it comes to race fuels and engine management systems these days. Typically old school leaded race fuels have very different specific gravities and end point temps. This usually means you put it in your tank and the tune becomes richer. You make power by leaning out the afr beyond what you can run on low octane and you advance timing beyond what you could normally run.

With unleaded race fuels usually its the same afr when you start but again you use the same strategy as the leaded fuel.

Now oxygenated race fuels are the rage and they can run leaner when filled in the tank and because they cary oxygen it will make more hp with no tuning...about 4 to 6%. These fuels make more power on the rich side vs. The lean side so they can sometimes have really good results on a factory tune.

Engine management systems vary in their ability to advance timing by sensing knock. Subarus have a abnormal amount of ignition advance available on top of the base timing map along with an agressive nature to seek knock and then back the tune off. This is why we sell so many engines :) Other more logical ems systems only have enough learning to take advantage of say 93 octane.

It has already been said but the only way is to either log the timing curve or put it on the dyno with race fuel and wait for it to learn.

How long does it take the ECU to adjust to a higher octane (91 to 93). I autox and I want to use 93 for events.

I'd like to know what kind of power increases could be had from race fuel WITH a tune.

Would it be similar to, or better than, what we're seeing from E85 cars?
@rice_classic

FRS is sensitive to anything under 93 it seems but i'm uncertain as to how much benefit there would be 93+ octane (on a stock car):

If you can't read french here are the results

Octane/hp/ft-lb
89/155/136
91/160/138
94/166/140

http://burn-out.ca/en/content/scion-...ne-test%C3%A9s

I know it doesn't compare 93 with 94 (or anything significantly above that). I wouldn't be surprised if the ECU can squeeze out a bit more timing on stock with race gas. But from reading this article I doubt there would be much power gains:

http://wot.motortrend.com/lights-cam...-s-339785.html

Drift Office might be a better one to seek out as he might have done this back to back.

I'm not a fan of E85 and have no intention of putting it in any of my vehicles, race car or otherwise, thus I have no data of my own.

im pretty sure the computer will take advantage of the higher octane fuel. how much advantage? we will see... it adjusts for octane lower than 93 im thinking is should do the same for higher octane. ive only put 93 in my brz but i will put in race fuel for a track day and see what happens.

This is a copy & paste from Jackson Racing RE: our cars & running on the track
It could be that they use a different engine tune and superchager for their opinion

However, they seem to know alot about our engines & racing




"
100 Octane (R+M/2) Unleaded Fuel -

It is important to run fuel designed for abuse at the

track. Even stock FA20 engines should run 100 Octane when at the racetrack to ensure

consistency and reliability. The additive packages in 91 Octane fuel are designed for

emissions and shelf life, while 100 Octane is designed for the high cylinder pressures and

full load/throttle conditions you will experience on the racetrack. When at the track, we

REQUIRE running a minimum of 50% 100 Octane fuel. We highly recommend running

75-100% 100 Octane when at the track."

Tank after tank of e85 around town and at the track...,could not possibly be any happier

Car runs great

Wanting to build out this motor next

From my experience with the 86/BRZ which is not extensive , it seems to work like this

Standard/stock ECU programming and ignition advance mapping expects 93 octane to run the full timing advance available in the standard maps and hence obtain maxium performance (with standard mapping)

93 USA = 98 RON
91 USA = 95 RON

If you put less than 93 (or some even some variants of 93) then the ECU will start to detect knock and based on the severity and frequency on the knock events it will retard the ignition timing by reducing the value of a parameter called the IAM (Ignition advance multiplier). This may reduce from say 1 to 0.8 will will reduce the knock control ignition advance by 20% across the entire RPM/load range. Rearly bad fuel can result in IAM falling to 0.2 or even zero, at zero only the timing the the base timing map would be applied, no knock control advance added.

Their are two main ignition advance tables,
Base timing table and the knock control timing table the total ignition advance is the sum of the two (plus/minus other offsets due intake air temp , coolant temp ect)

The Base timing is always used then the knock control timing is added

Total timing = Base timing + (Knock control advance timing * IAM)

Their appears to be no facility in the tables/mapping to further advance the timing if greater than 93 octane fuel is used. However some blends/brands 93 fuels especially in Canada seems to exhibit knock, which can reduce the IAM and hence lower performance.

Once you IAM is at 1 which happens with decent 93 fuel their is no further advance options available to the ECU. (unless you remap/change tune maps)

Knock control is a continuous learning process and once the ecu detects no knock for a couple of minutes it will start to move the IAM back towards 1 and restore your full timing advance, ie when you fuel up with a better quality fuel.

Conversely if the knock events continue the ecu will keep reducing the IAM (hence reducing ignition timing & performance ) until the knock gets down to a level "acceptable" to the ECU programming.

Fuel trims are also continuously learned and adjusted, their appears to be no benefit in "resetting the ecu" other than to clear fault codes. The ECU will to the extent of its learning capacity and fuel/ignition mapping learn changes in fuels ie 91 to 93 or E10 non E10 fuels

further explanation here knock control
http://www.ft86club.com/forums/showp...09&postcount=1


info on fuel trims and open loop closed loop modes
http://www.ft86club.com/forums/showp...59&postcount=1

Torco Accelerator
 

I use Torco Accelerator to bring up the octane number. Adding 16oz Torco accelerator to a full tank of 91 gas and the car run way peppier and smoother. I'm running OFT stage 1, and on 91 gas the Advance multiplier fluctuates like crazy, sometimes drops to 0.5. When I add Torco accelerator to 91 gas the Advance multiplier always stay at 1

Bringing a thread back to life....

So, any issue with running 9 gallons 91 octane mixed with 1 gallon a 100 octane to get 92 octane (or 2 gallons 100 octane to get 93)? boosted with tune for 92 octane...

No Issue at all. I use 92 day in day out. and 100 for RallyX then switch back to 92 after. Only reason to go higher octane is to reduce knock to keep the Advance multiplier at 1.


I noticed that when I ran rally at 92 only my multiplier would go down to .8 after a run, putting in the higher octane helps the car be happy at full throttle :)


If you're not racing or doing anything special there's no point.

I find my boosted 86 feels considerably more powerful when I add two and a half gallons of Trick 101 to the 92 E0 in the rest of the tank. Probably brings octane up to around 94 and would really like to see the difference on the dyno (Perhaps next time I go to Drift Office we can test it). I have run 3 or 4 tanks like this thru the car, but generally do this when autocrossing and see no change in fuel consumption.

I generally run 100 or 105 when I go to the track with the turbo. It feels pretty damned good.