....and the number one thing to remember with avgas in the 500 is leave the boost pump on all the time!!
Otherwise youll be explaining the auto to your boss or insurance company.
I think its 25% max by volume.
I once saw an AS350 that had been running straight avags, white exhaust pipe so you can imagine what the NGVs looked like.
Great movie Deadly Encounter, i hear Larry H had a pilots licence at the time.