I once flew from Tulsa to Atlanta.
The guy seated next to me was a petroleum engineer. He really knew his stuff and it was interesting.
I can’t recall much but one thing was the scale is really on a thousand point scale. In other words 98 octane is 98 out of 1000. It only takes a tiny increase to make a big difference.
Also back in WWII we produced 115 octane aviation fuel and it made a difference in performance.
“Many people think high-octane gasoline is more powerful than low octane gasoline. This is not true. The energy produced from a gallon of high and low octane gasoline is almost the same. Any minor variation depends on what additives are used by refiners and blenders. The key features of high-octane gasoline are a higher ignition temperature and a slower burning rate.
The higher ignition temperature of high octane gasoline reduces the chance of detonation from “hot spots” within the engine’s cylinders and minimizes pre-ignition. A slower burn rate allows for more efficient use of the ignited fuel’s pressure buildup to be converted to mechanical energy instead of heat. That is why a high performance engine will run smoother and will feel more powerful when high-octane gasoline is used.
Using a low-octane gasoline whose ignition temperature is too low causes pre-ignition. Low-octane automotive gasoline (87-octane) has a typical ignition temperature of 300 degrees Celsius; high-octane (93-octane) automotive gasoline has a typical ignition temperature of 400 degrees Celsius. Aviation gasoline is blended to ignite at 500 degrees Celsius. High compression and high cylinder temperature will cause the fuel to ignite before the sparkplug fires.” http://www.aviationpros.com/article/10387611/octane-101-autogas-vs-avgas
“Also back in WWII we produced 115 octane aviation fuel and it made a difference in performance”
Basic thermodynamics says that a higher compression ratio results in a more efficient engine. A higher compression engine requires a fuel with more resistance to pinging (detonation) which will damage the engine. Higher octane gasoline simply has better resistance to pinging. It has no more energy per pound of gasoline.
The airplane engines needed to get as much power as possible per pound of engine weight. The cost of the fuel wasn’t important.
Meanwhile, jet engines couldn’t care less about octane rating. The plane problem is solved but we motorists care how much it costs to drive a mile.
I don’t want a higher octane fuel unless it means I can drive cheaper.
Trivia: Jimmy Doolittle was responsible for creating of 100 octane aviation fuel in WWII. Shell produced it, but Doolittle envisioned and demanded it.
68inHg manifold pressure supercharger?
Yes, but that 115 octane stuff needed TEL (tetra ethyl lead) to reach that octane rating. It was produced all over the UK in WWII and later for auto fuel. Just like the US, it was phased out for auto fuel in the 80's.
Now the only source world-wide for TEL - used in aviation fuel - is a single plant near Port Sunlight on the River Mersey - cue Gerry and the Pacemakers...:^)
The Germans had trouble producing anything we would have called aviation gasoline because of the bombing campaign they were under.