AV gas?

The addatives for 104 Avgas are very different to those suitable for a race car so you should consider adding UCL or an anti wear additive if you use it. Its big advantage is no ethanol otherwise performance wise I have tested both on the dyno and the difference is marginal at maybe 5 hp at the wheels. The ECU on the 355 is simply no programed to recognize the higher octane to benefit from a slightly greater advance curve. With turbo charging of course its another story.