Mitch Alsup (Mitch_alsup)

I would think that high octane fuel would be kinder to cats than low octane fuel. It burns at a lower temperature (slower) so the whole exhaust system is operating in more benign conditions. It, generally has lower amounts of sulphur and other things bad for cats then lower grades of gasoline. In the limit, 110 race gas is 40% tolulene and 45% xylene with 15% detergents and other additives that drop the octane from 116 (T+X) to 110 (T+X+<stuff>).