If you search for 'octane' in the list of universal OBD parameters attached, you won't find any matches. That doesn't mean that a modern ECU doesn't have some sort of way to respond to knock. There is no universal parameter to log knock learning; you'd have to read RAM addresses directly, with an application-specific tool.

As I mentioned above, there are more sophisticated ways knock control can be done. It's not just interpolating between maps intended for high and low octane, although that's what say Mitsubishi has typically done. Up until now at least, Subaru hasn't been doing it in exactly that way. Here is a very good writeup on the Subaru knock-control system, at least up through the current WRX/STi http://www.romraider.com/forum/viewt...hp?f=25&t=1840

So in a nut shell, going higher that 93 in octane without a proper tune would be a waste right? With higher octane requires more timing advance amongst other changes because of the resistance to ignite. But the factory ecu can only advance so far before reaching its limits on how much it can change

Leaded fuel will poison the o2 sensors which means check engine lights. I would be surprised if you noticed anything from 100 AKI unleaded race gas. I threw some 100 octane in my push mower once. It smelled pretty cool but it was still a regular old mower.

Great info in here. arghx7 what do you do?

And I'm pretty sure I've seen you on another forum before

I'd rather not say.

He's obviously a very knowledgable landscaper.

Heh, jk...

Since there are lots of knowledgeable folks on this thread.. I've got a related question about 91 vs 93 octane. In CA only 91 is available except for a very few places. I've considered adding about 3 gallons of 100 octane to the 10 gallons of 91 in the tank. This would bring up the avg to 93 or so.

Any benefit to this?

Since it would be mixed going forward, I'd just periodically add some more 100 when I pass that gas station. If it's not done right I could see the octane rating going well above 93 (and also wasting money on too much 100) ..

I'm not as concerned with performance as avoiding any kind of knock and forcing the ECU to relearn the 91/'low octane' thats being used on a regular basis.

I wouldn't do it all. The difference you'll see in regular driving will be negligible but the difference you'll see in the thinning of your wallet will easily be noticed.

Just pump 91 for daily driving. Save the expensive stuff for a day a the track.

I knew there was a reason I wasn't getting any work!:paddle:

Thanks Dimman I needed to laugh today...

One aspect of modern vehicles that you will have to accept, all modern engines knock ,especially at low load high timing and AFR. What you have to be concerned with is knock that is consistent, and happening during high load, open loop operation. To a certain extent the the engine will correct the reason for the knock (either retarding ignition timing, increasing fueling, or a combination of the two). If the manufacturer did not want the vehicle to be run with 91 octane than it would not be sold in your state with a warranty. I live in New Mexico, and our gas is as bad as yours, interesting as we are so close to Texas... I degress. Anyways, your vehicle will not be at it's most efficient running 91 octane, only you can decide if the extra $5.00 to $8.00 is worth spending every time you fill up.

And also Rice, yes ALL OBD II ECU's have a octane parameter built into the factory ECU system, whether it is determine proper ignition, fueling, or different alpha N calculations (Honda) for the cylinder events. Yes different automobile manufacturers have different ways of dealing with knock, but ALL have a sub routine to change the octane count on the fuel once it is detected.

Jedibow: in asking if all OBDII ecu's do that, I wasn't referring to ignition management via knock control. That I knew. I was referring to auto-advancing to take advantage of higher octane than what the car was designed for. My 1996 Ford Econoline Van designed to run on 85-87 octane doesn't seem to "figure it out" when I've put in 93 octane and I have a sneaking suspicion that most OBD2 ECU's are not "adaptive" like the Camry 2GR. The discussion wasn't based around retarding once detecting knock, it was based around automatic detection of higher octane for specific design and subsequently automatically altering ignition timing.

All OBDII ecu's retard timing when knock is detected. Check
All OBDII ecu's on cars designed for 87 octane automatically detect and advance timing when higher octane is introduced than what the car was designed to run on? I don't think that's true.

But.. :iono:

I have this suspicion that it's like this, if the car is meant for 87 then it might not have a high octane map onboard, but if it's tuned for 93/91 then it can detect the higher octane after it's been drinking 87 for a while?

:iono:

Sorry, only certain ECU's are proactive to determine what ignition timing and fuel tables to run, namely Toyota, Subaru, and Volkswagen mostly. Most ECU's are reactive, and only retard ignition as they see knock, so the maximum timing it will run will be the value on the timing map (they cannot exceed these values) unless effected by a multiplier table such as barometric pressure, or tempurature adjustment tables.

I would also like to state that even though subaru ECU's are proactive, there is also a maximum value that the ECU would apply for timing, and no it would not take full advantage of using 100 octane fuel.

I'm sorry I hope that clears things up a bit, I've had a lot going on lately and have been in a bad mood. Again I'm sorry.

One thing to keep in mind is that an ECU really consists of 3 things:

1) Hardware (injector drivers, analog inputs, CAN communication, processor, RAM, flash ROM, etc)
2) Software (the way things are calculated, not the actual values in the tables)
3) Software calibration (the tuning of the maps and values inside)

Software is being developed all the time, but it's not always changing on every engine. If you've got an old engine on a vehicle that doesn't change much, it may have old software. That cold mean old knock control logic that is mostly reactive in nature. The manufacturer isn't going to update it unless they feel it's necessary to meet an emissions, engine output, or driveability/NVH (noise/vibration/harshness) goal--development time costs money.

Look at the WRX and STi for example. The main non-emissions calculations inside have barely changed in 10 years. Some stuff shifted around when they went to electronic throttle, AVCS (variable valve timing) and a 32bit ECU, but that's about it. The EJ series engines are 20+ years old.

When a mostly new engine goes into development, you can expect some of the newest software to be implemented. So it's less about the make (Toyota etc) and more about the individual needs of the vehicle under development.

Btw, much of this software is developed in collaboration with suppliers or purchased off-the-shelf. Sometimes most of the engine tune is outsourced to a company and you never hear about it. Here is a partial list of the main suppliers of ECU and ECU software/control logic:

Denso
Yakazi
Hitachi
Delphi
Siemens/Continental
Bosch
Magnetti Marelli
Renesas

Most German makes use Bosch or Siemens. Toyota uses Denso on almost all engines; Subaru uses Denso a lot but dabbles in other brands. Nissan uses Hitachi. Hyundai uses Siemens. GM uses Delphi and Bosch mostly; Chrysler uses Magnetti Marelli stuff. I don't know every supplier used on every project, but it's perhaps half true to say something like "Volkswagen ECUs respond better to low octane than others." VW/Porsche use various versions of Bosch software anyway.

Hope that clears some things up.

I wrote engine models using Simulink that ended up in Delphi controllers... arghx7 has/is working in industry :)

What he's trying to say is that if you increase the octane you will see more ignition advance which may lead to more power... IF there isn't ignition advance limits.

What he's not said, which I think is important is that with the increased octane you will not have your knock control strategy retarding the ignition advance... which means that the ECU won't reduce the power output... which conversely means that you'll be making more power.

For the poster that was saying that you won't be able to ignite higher octane fuel... that's a fallacy. You could run 100 octane in your BRZ/FRS and you're not going to have the thing misfire. This isn't like trying to start an engine running on E98 when it's 40 degrees outside.

If you study the combustion process in the cylinder a bit more you'll see that it's the temperature and pressure the end gas sees near the cylinder wall is what the addition octane is there for. Once the flame kernel reaches the end gas it will be ignited... no problem there. For fun think about the in cylinder temperature and pressure that the end gas sees... degree by degree. It'll start making more sense.

My turn. I put 100 octane in my 04 Solara v6, it has an 11.1:1 compression ratio which I'm pretty sure was damn high back then. I disconnected the battery for 30 min to ''reset'' the ecu and off I went. I drove her hard like I usually do and thought I may have noticed a slight increase and smoother running but it was most likely due to placebo or simply ambient conditions. However, the reduction of the weight of my wallet was significant. I read that the FR-S will infact make more power on 93. I do believe that above that there are little to no gains to be had with the stock ECU.

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.

I just want to increase the octane of the crap California 91 gas. I'll be boosted down there and looking at 2 maps, 6psi for California and 8psi for everywhere else. Sucks to lose 20 hp due to 1 octane.