mark kibort

the mixture can be the same (same mass of air and fuel ratio), but the power can be lower. adding more fuel, changes the mixture, but doesnt nessarily give more power. if you want more power vs what you loss by the E85, you need to add more air.....and that is why they can run more advance, scavenging cams, and higher compression to take advantage of the higher octane.

usually the ecu doesnt adjust for octane.. in a way it can, but its after the fact... by sensing knocks and retarding timing.

this allows for higher compression, advanced timing and cam profiles to use the E85 fuel.

Octane allows for more compression, ignition timing to reduce the chance of detonation. its not really cheap race gas.. it has an entirely different optimal fuel air ratio, that requires MORE fuel to completely burn or to produce max power .The problem is , the 10% or so more fuel you need to burn, takes the place of the air that you need to burn it. so all things being equal, you will have a reduction of near 10% in HP if nothing else changes. its those changes that can make a deficit , a benefit. thats how ive come to understand the trade offs. true??

David993S

^^ This. When one factors in the total production costs (fuel for farmers to plant and harvest the corn, transportation, etc.) it takes more than a gallon of gasoline and diesel to produce a gallon of ethanol.
And that's not to mention the govt. subsidies and what it's probably doing to the fuel lines in my old Alfa.

NYoutftr

LNE
Just released another Tech report discussing on how fuel additives can help.
I have never seen any results from additives.
Any opinions?

promocop

For street use, is there REALLY a difference between "premium unleaded" and "regular unleaded" Doesn't the engine's computer compensate? Often wondered this

AO

The draw for e85 is that you can run more advance timing because e85 is quite resilient against pre-ignition/detonation/knock whereas gasoline is prone. However, there are tradeoffs.

if one were to get actual e85 (i.e. 85% ethanol - e85 from the pump can be anywhere between ~50% to 90%) the en ergy density for e85 is about 72% of gasoline, so you need to burn more e85 to get the same effective power. But because you can run more advance, you can "turn it up to 11" and get even further gains.

Getting back to the OP question, E10 is reported to have 98% of the energy density of gasoline. There is really very little difference between 92 octane and 93 octane. All [modern-ish] cars in the US are designed to work with 91 octane or lower - thanks to California . So in theory (in practice may be different) given the choice between E10 @ 93 octane, vs 100% gasoline @ 92 Octane, I would choose the 100% gas at 92 octane, because you should see a slight (~2%) increase in power because the engine management system will flow the exact same amount of fuel but it will have a higher energy density than E10. That's equivalent to a gain of 4 to 10 WHP (depending on the original output of that engine) which is quite a bit in my opinion. Also the there should be no difference in detonate/knock in that engine (because it has to be able to run on 91).

Of course, if the car was "tuned" for 93 octane, then you should use the 93.

NYoutftr

That was the dilemma, the car has a Evoms Stage IV tune, based on 93 octane

Balr14

I have a friend with a ZL1 Camaro and a CL55 AMG, both converted to E85 by replacing injectors and getting a tune. Both got significant horsepower and torque gains at a cost of about 10% in gas mileage. But E85 is about .50 cheaper than premium gas around here. So, it looks like a pretty decent swap. I wonder if that would work for a 997.2?

cstyles

I posted in that Canadian thread linked above. One thing I mentioned was how much subjective opinion gets thrown around in these discussions. Unless someone is providing objective data, it's just an opinion and usually an unfounded or biased one.

I can only give facts for the 997 Turbo. The factory ECU is programmed for 93 octane. Running Shell V-Power 91 octane 0% ethanol 'pure gas' results in the ECU pulling timing at wide open throttle.

Using 94 octane with 10% ethanol content, the ECU pulls much less timing. Could I feel the difference from the drivers seat? Absolutely not. But the data proves that in the 997TT, higher octane is the preferred choice even with 10% ethanol. This was backed up by other turbo owners with the ability to data log. Therefore, only 94 E10 goes in my car. Of course if we had 94 with 0% ethanol, I'd data log that and use it if it was equal or better than 94 E10.

Here are my interactive data logs That I posted in that thread. Lots of interesting data you can pick and choose to overlay on top of the base RPM graph.

94 E10: https://datazap.me/u/cstyles/stage-0-2-pulls?log=0&data=18-23-24-25-26-27-28

Shell V-power 91 0% Ethanol: https://datazap.me/u/cstyles/shell-91-stage-2-91acn-stage-0?log=1&data=18-23-24-25-26-27-28