Octane boosters
Inspected a couple of cylinders from an air cooled test engine recently
1 Unleaded with Castrol booster
2 Unleaded with Tetra Lead
Both were clean, no corrosion, no fouling. Plugs were clean. Valve seats and valve faces normal.
Many years ago the BGA conducted some tests on 4 star fuel. They used a Beagle Airdale at the time and the tests were overseen by their Tech man Dick Stratton.
Tugging is as good a test for fuel suitability as anything and does not involve a passenger,plus the tug is usually within close proximity to an airfield,so perhaps the BGA can be prevailed upon to help out again.