E85 timing question

Ok so I have a question.... Since Ethanol burns faster then 93 octane, and say I advance my timing 4 degrees give or take, should I also then change the timing table on the E85 to take an additional 4 degrees out ?

I have been in so many circles trying to find the truth about ethanol combustion given there is so much conflicting information from anecdotal internet reports, non-scholarly/non-technical articles, scholarly/technical articles, looking at stock GM calibrations for flex fuel applications. Its almost like every example you see conflicts with each other.

With all that being said and trusting that GM puts accurate calibrations into their tune files since they spend millions and have the worlds most capable equipment and labs, I agree with you that ethanol "burns faster" so therefore, it would require slightly less timing, which looks around to be what you said of around 4 degrees based on the Alcohol timing correction table in a GEN V flex fuel 5.3.

However, I see where "tuners" are running 30-32 degrees of max timing at WOT with ethanol. This seems too much.

Anyway, yes I think you should take out 4 degrees of timing using the alcohol modifier timing table. Hopefully someone will come in with some documented info backed up by maybe some SAE articles or peer reviewed literature and evidence.

At part throttle, E85 needs less timing but at WOT you can run more timing due to its cooling capability. As a VERY general guideline you should remove up to 4 degrees of timing at part throttle and interpolate/smooth to +4 degrees of timing by full throttle. Each car is different so it all depends on how the car drives. In my opinion it is easier to tune the timing for 93 octane and then use the Alcohol Spark Modifier tables to max add and max reduce timing values for E85 and use the multiplier table for Ethanol percentage so that it adds/removes a portion based on Ethanol content.

I took out a degree and a half out of the E85 timing across the board, with the horsepower calculation, it showed a gain of 32 hp. My 93 octane tables are showing 26 degrees at idle and goes up slightly. Hoping my wide band comes in so that I can tune the air and fuel to better map the timing.

on E85 there is no knock or detonation, so you can go max of timing until the power of up stopping .

I would say if engine is limited by knock on gasoline at high load (not reaching MBT) and you switch to Ethanol, this is where you could add timing and make more power. If not there is probably no reason to add timing and it wont make more power. Actually, when I ran E85 I tested and raised it and did not get any knock only to realize it went slower at the dragstrip and backed it down again. On a gen 5 L83 with free flowing exhaust and no cats it was fastest at 20-22 degrees at high load high rpm.