Trying to understand how timing is advanced in regards to octane
10-25-2014, 02:46 PM
#1
Trying to understand how timing is advanced in regards to octane
Gents,
This subjected has probably been glossed over at some point but I haven't been able to locate it. So my question is, how would the ecu know what octane gets put into the tank and what is the theoretically limit out of the factory in terms of usable octane?
- Reason why is due to a very fast fellow board member mentioning that he always runs a mix of 91 and 100 octane. He doesn't have a race gas tune, but an optimized 91 octane tune and runs very well with this mixture.
- At WOT, does the ecu go for max timing based on previous maps and then adds/subtracts timing based on current events (i.e IAT, load, knock sensor, etc data)?
- After reading about the fellow board member, I've been mixing 91 and 100 octane and swear I can feel a difference over time (2 weeks). Am I going crazy or has anyone ever quantified this with numbers? TIA
This subjected has probably been glossed over at some point but I haven't been able to locate it. So my question is, how would the ecu know what octane gets put into the tank and what is the theoretically limit out of the factory in terms of usable octane?
- Reason why is due to a very fast fellow board member mentioning that he always runs a mix of 91 and 100 octane. He doesn't have a race gas tune, but an optimized 91 octane tune and runs very well with this mixture.
- At WOT, does the ecu go for max timing based on previous maps and then adds/subtracts timing based on current events (i.e IAT, load, knock sensor, etc data)?
- After reading about the fellow board member, I've been mixing 91 and 100 octane and swear I can feel a difference over time (2 weeks). Am I going crazy or has anyone ever quantified this with numbers? TIA
10-25-2014, 02:55 PM
#2
MBWorld Fanatic!
Ecu will adjust considering KR and iats, also you can in theory add more octane but only if you were running leaner that normal and to be safe but more likely than not you will not get added power.
10-25-2014, 02:56 PM
#3
MBWorld Fanatic!
I have been logging for a few weeks now and will be asking some questions after monitoring this thread regarding timing and rich/lean. Maybe they will be answered in this thread before I create another or derail this one 
I just found this article. Answered most of my questions. Maybe will answer yours.
http://www.enginelogics.com/engine-management-basics/
I just found this article. Answered most of my questions. Maybe will answer yours.
http://www.enginelogics.com/engine-management-basics/
Last edited by 2000UZJ; 10-25-2014 at 03:07 PM.
10-25-2014, 03:13 PM
#4
As I was driving through parts of New Mexico where the highest octane available was 89 octane, one could imagine the ECU engineers for-seeing this type of event and would bump down the timing so save the motor. I'm guessing the only way the ECU can see this is by seeing knock events correct?
Conversely when the tank gets filled back up with 91/93 octane, will it just see that knock has been reduced thereby bumping the timing back up till it reaches that "safe" threshold?
10-25-2014, 03:17 PM
#5
MBWorld Fanatic!
Actually all new cars ecu do that. I know which member you are talking about and it's done more for safety than anything else since his track runs were in colder weather than his tune
10-25-2014, 03:26 PM
#6
