340-40=300miles
9 gallons over 300 miles = 33.3mpg for the Volt’s engine.
9 gallons over 340 miles = 37.7mpg for the Volt’s engine and battery.
Overall FE for the Volt seems decidedly unimpressive on long trips.
If we go with a 6 gallon tank and the stated 340 mile total range we get 56.6 for the engine and battery and 50 for the engine alone.