2-So you are basically agreeing with me? But in the sense that the ECU will do it backwards ei: from 93 to 87, but then you believe it cannot do it from 87 to 93? This is where what I have been saying fall into. It will advance the timing until a knock is detected.
If Im not mistaken, B3 is an engineer.
Anyhow, I think that looking at these ecu programs as different maps is a little odd. I think it is more like a different range of the same map. Therefore, if the car has enough range to accommodate spark knock from different grades of gasoline (forget E85 for the time being), and run normally and efficiently withing those ranges, using premium on a vehicle is recommended to run on lower octane can yield some improvements in performance.
Also, no car is designed to knock. car with knock sensors are designed to adapt to different knock situations. The ecu will attempt to maintain the most efficient range of timing advance for the situation (load, temp, octane etc.) which in many situations is just below the knock threshold.
Old cars are designed to stay well below the knock threshold, and will probably not benefit much from an increase in octane without the user making changes to the timing.
Along these lines, my QX4 will loudly complain if I do not use high octane fuel on hot days. It appears to me that it does not have enough timing adjustment to eliminate knock in some situations. The Corrado on the other hand, has never audibly knocked even when presented with boost, though I have observed the computer recording knock vents in vag com, and pulling timing as a result before the knock becomes damaging. Amazing to me considering the Corrado is 8 years older.
I wanted to dust off my old books on design constraints for the SSME HP fuel turbopumps and have a technical discussion on graduate level engine studies. To my knowledge, they never did solve the issue of in-flight restart. That was a major reason for the rebirth of the J-2X program.
But alas, you have chosen to take your marbles and go play elsewhere.
"You'll have to answer to the Coca-Cola company."
You can only advance timing so much until you hit MBT. You will not increase power beyond that. If you hit MBT without knock, higher octane is not doing you any favors. I have no idea WTF point B3 is trying to make. I just hope the rest of us understand that running higher octane than what your engine can tune for will cause a loss of power but is not dangerous.
Just as an interesting aside, my 190 was designed pre-knock sensors. Instead, MB used something else pretty interesting. On some models, they included a rotary knob in the engine bay that when turned to different positions, changed resistance, which effectively told the very simple ecu to choose a different timing map.
On others, like mine, it is a simple plug and play resistor. In the 80's it was assumed by MB either that premium fuel was not widely available in the US, it was of lesser quality, or that owners would not want to use it, so the car was equipped with a resistor that chose a map with 6 degrees of retard. A popular 'mod', since there are no chip upgrades for this generation of vehicle, is to unplug that resistor entirely which equates to infinite resistance and (there is some debate on this in the MB forums) causes the computer to choose a map with no retard, boosting performance a bit (at the cost of requiring premium). The idea with the dial was that, depending on what gas was locally available, you could manually adjust the amount of spark advance.
1987 Mercedes 190E 16v Cosworth
1997 Volvo 855 T5
2010 Volvo XC90
1975 Honda CB400F Super Sport
1986 BMW 535i
1984 BMW 745i turbo - FOR SALE
2002 Passat 1.8t
1990 Saab 9000 turbo
Well I'm not going to try a start any arguments with some of the smarter guys here. I am not way an expert on engines, and ecu tuning. I know some, but definitely not as much as the few that are arguing.
Anyways, my old car was tuned for 93. It had 2 main maps High Octane and Low Octane. While driving around in a Closed Loop, obviously the oxygen sensor would try and keep my AFR ratio as close to stoich as possible and ignore my Fuel maps. And my EGR Advanced Timing map would add to my existing Timing Tables. This all happens during Closed Loop with MY old car. So if I went with a higher octane and still wanted to stay in closed loop (Load under 100 for the most part) then I would not see any hp gain but maybe slightly better mpg.
Now with Open Loop is a different story. All oxygen sensors are not used and my High Octane and Low Octane maps are in full effect. If the car runs and does not knock, whatever my High Octane table said, the injectors try to match it and my timing is whatever my timing table says it needs to be. If we hit knock, then ECU pulled 1 degree of timing per 3 knocks. Also my ECU had logic where the engine sees knock constantly then it used low octane fuel and low timing tables at ALL times. If this happens, something is wrong.
So having said everything above in regards to open loop, I would not really see higher HP numbers when using higher octane when I was tuned for 93 since timing and AFR would stay the same. I would see higher HP number if I retuned my ECU for the higher octane since I would be able to advance my timing or when I tuned for e85, I was able to lean out and advance timing like no tomorrow and gain 50whp + but then you have MBT to worry about.
I'm only familiar with my car and my ecu. I have no idea what other car manufacturers do and program their ECU, but I would imagine their logic and technology changes all the time how timing and AFR is derived.
Is it safe to say most new cars could benefit, in performance or mileage, from higher than minimum octane fuel if programmed to take advantage?
knock sensing adaptive ignition systems nearly across the board
relatively high compression engines nearly across the board
Whether its worthwhile is a whole other can of worms imo.
I have taken higher level engine design courses and have participated in Formula SAE. I have a few pubs that I keep on my book shelf. My knowledge about these things sometimes can be wrong. Just like any of us can be wrong as we are not experts on the subject matter; however, I have had some introduction to a lot of these concepts.
I still stand by my original comment that modern engine controls can and will accommodate a the array of fuel available today (87 through 93). It is also easier for a manufacturer to simply recommend Regular vs Premium since the gas prices as pretty high these days and even luxury brands are now calling for 87. Also using 91 or 93 wont degrade engine performance, if the ECU cannot accommodate for it. It simply will burn it as if it was 87. If there is a loss it is minimal and not even noticed, because I certainly have never noticed it.
I am a car nut and I have turn wrenches for many years. I simply love all things mechanical, but I certainly do not know it all, even though sometimes I think I do and it is wrong to think so. Pure fact of the matter is, all of us have said something wrong in this thread. I certainly have, particularly with the 100 Octane comment early on.
Now let see if we can, with proper knowledge arrive at a reasonable conclusion.
What is being disputed is that it is a common practice for cars originally designed and tuned to run on 87 octane to significantly improve their performance if 93 octane is used.
B3sat16v would rather ask for qualifications and education background than provide proof that this is a common practice.
Of course it's company policy never to, imply ownership in the event of a dildo... always use the indefinite article a dildo, never your dildo.
And I asked for proof because some of you do not seem to know how modern systems and controls operate. It is better for a manufacturer to design an ECU that will run all Octanes available and then just recommend 87 (A lot of people like to run cheaper fuel), but also make it known that the car will perform better with Higher Octane. This covers a higher array of drivers. Electronics are cheap and fast today and it is easy to store more data in ECUs. Have any of you seen the CR on these new cars calling for 87 Octane? Some have it as high as 10.8:1.