[Avanza]

^^^^
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Let’s proceed with caution here. RPM and bore size also affect the combustion events. In general -> smaller bore and higher rpms are beneficial to detonation margin. Extrapolating for more than one variable can be make things end badly.

If I remember correctly, about ten years ago, Kevin Eldrege of ACE-performance built a PV IO-360 engine with 10.5/1 compression ratio,
This engine was operated with mogas without and with ethanol but I´m not familiar with the ignition system they were using.
They later developed their own cylinder with larger valves to make even more power.
However this project stalled later on for business related reasons.

Good luck

 

[wsquare]

" Why not do what has already been proven for 100 years of aviation - ADI? A simple aux tank with a few gallons of alcohol, a simple pump, and a nozzle aimed down the throat of the servo should cure a lot of detonation worries. The Reno guys have been doing it for a long time. A simple MP switch turn on the pump when needed."

Interesting approach. A few thoughts, mainly for clarification.

What is the "throat of the servo"? I have a carb with a throat, but not sure I have a servo.

What is a "MP switch"?

How does one install a nozzle in the air/fuel induction system of a carb? This doesn't seem to be a trivial matter. What type nozzle? Size of orfice? Etc. Is there technical information? I'm interested in learning more.

Assuming 0-360, 9:1, carb, fixed mags -- what should the alcohol injection flow rate be? What type of alcohol (specs)?

Carbs are known for uneven distribution of fuel/air mixture, for various reasons, is there an increased risk of detonation if the fuel/air/alcohol mixture is uneven across the cylinders?

Is there an altitude where the alcohol is turned off/on due to detonation risk from using 91 unleaded at lower altitudes? Is there technical basis for a given altitude?

What does alcohol do to the combustion process such that 91 octane unleaded can be burned at lower altitudes without fear of detonation?

Is there an increased risk of other adverse effects on the engine from using 91 unleaded -- such as valve guide wear, valve recession, etc?

Is there an increased risk of other adverse effects on the engine from using 91 unleaded combined with alcohol -- such as valve guide wear, valve recession, etc?

Thanks for considering these thoughts. I there a good reference on this concept? It is likely a good idea to explore all options for using lower octane unleaded fuel.