In my experience, “non-ethanol” does not always equal completely “clear gas”. I’ve seen quite a bit of variation from station to station in color. Most has a light green sheen to it so it makes me question if it’s truly 100% ethanol free. My hunch is that if it’s not from its own dedicated pump, there may be some regular gas left in the line. As best practice, I always drain my carb after a track day to be safe.
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The last race I went out and had no pace at all, data from my Alfaro seems to indicate that the drop off was all over the lap. I had no handling issues and later put the chassis on a table - it is straight. During the race and test day (day before) I was way off the pace (nearly two seconds on a 50 second lap). I thought it might be carb or engine related, but I switched to a backup motor and did not improve. I had an engine builder look at both at the track, we couldn’t tell anything was off. Carbs looked okay. I had another engine builder look at the second motor afterwards, he couldn’t find anything obvious - the idle jet was a bit clogged.
I was hitting redline around where I normally do, the engines did not feel that bad, apart from an inconsistent idle. A few of my buddies said I looked slow off the corners… Could it be that the fuel I was using had just gone bad? It is non-ethanol that I have had since July 15th or so. That would explain at least why the pace was bad on both engines.
Follow the 206 rule book, its all 87 pump gas.
Most engine builders (in my limited research) determined the 206 runs best on 87 octane fuel. Personally I run non-ethanol, but I’m also (continiuosly) suprised how gummed up my carb gets (even using non-ethanol) after sitting a month or so. 
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I don’t think it would make less power as it doesn’t hurt to put higher octane ratings in lower compression engines but it’s just a waste of money honestly. Its like filling up your Camry with 98, no performance benefit it’s just safety for the engine.
Marathon/Speedway/Meijer 87 octane E10 gas is what Briggs jetted the engine with originally.
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This is missing the fact that a slower burning fuel (higher octane) effectively retards the ignition timing. This can actually lead to a marginal decrease in performance and increase in heat rejected through the exhaust. Not a whole lot by any means though. Just a slight correction.
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Octane is not related to flame speed though. That’s a common misconception.
Modern cars don’t necessarily need to be “performance” models to benefit from higher octane fuel. They have the ability to adjust ignition advance. The increase is more nuanced compared to higher output engines but it’s a thing.
Wether it’s worth the extra cost or not is up to the individual.
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Burn speed and flame speed are different. Burn speed can increase due to localized pre-ignition so the full quantity of fuel burns faster than if it relied on the flame front alone. Even without audible knock, there can be trace amounts of this happening. I won’t say that cars won’t increase timing, but typically they don’t. There’s a base table that gets pulled back with knock, but adding to the base table was at least never done when I was an engine controls developer. The application engineers got really squeamish about the idea and didn’t want to give the software the power to do that. Regardless, my comment was more directed to the fixed timing engines we run in 206.
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I defer to your experience and knowledge. Curious on difference between flame speed vs burn speed but that’s probably another topic. Calibration is super interesting to me.
For the ignition timing I was talking more about the Camry.
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Keeping within the scope of this thread, “burn speed” is kind of vague and context-dependent. If the vapors in an engine only burned at the flame front, then burn speed would be equal to flame speed. However, the entire cylinder is pressurizing and has local hot spots (like carbon shards that can glow like lightbulb filaments), so you get pockets of where the mixture can burn ahead of the flame front. The cylinder is rising, so there is compressive heating going on, and the flame front is sub-sonic, so there’s a pressure wave traveling ahead of it on top of that.
Basically, in the context of a running engine where there’s a lot of things happening all at once and none of them are prefect, the total amount of gasoline inside a cylinder can get burned faster with lower octane.
The funny thing with “burning” is that it is just a fast sub-set of oxidation. The oxidation of aluminum in Thermite turns it into an explosive; it’s just super fast compared to the normal oxidation of aluminum that is boring. It’s also why oil rags in an enclosed container can catch fire; they are actually “burning” the whole time but the very, very low heat they produce is trapped and builds until it runs away. So even those these time scales are in days vs. milliseconds, it’s the same underlying stuff.
Now, in now way am I claiming that there’s a huge, dramatic difference between regular and premium. That only comes into play in the real world when you are at the border between unstable and stable. The farther you are away from that border - in either direction - the less the fuel matters outside of a theoretical sense.
The timing should always be more retarded than the operator
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