Originally Posted by Max...
Sadly I am old enough to remember 4 star - I suspect the high octane 4 star we grew up with was like rocket fuel in comparison to the bio-crap EU-juice we get now...
In what way?
High octane fuel does not burn hotter or more powerfully; it's simply harder to ignite. Octane is a burn retardant.
Higher octane fuel is designated for high performance engines because the higher compression ratios would pre-detonate lower fuel grades. The higher octane fuel will delay ignition until there actually is a spark.
That said, ethanol-laced fuel has a (very) slightly lower energy content than straight gasoline, but tends to increase the octane rating compared to (not the actual octane content.) That's assuming I remember the science correctly.