My brother and I have an Andair fuel selector valve in our -4. We have a 160 HP, 8.5 compression ratio engine. We use 93 octane or 100LL in the left tank only and 100LL in the right tank only. Anytime we are in the pattern we are on the right tank, so we are using 100LL on take off or landing. We have the same arrangement on our -7A with 180 HP.