throttle position and at what intake manifold pressures real world measurements show that under level steady state interstate highway conditions there will be only some 7 10 psi positive pressure in the intake manifold during some 85 or 90 of the time on the road which means that 85 90 of normal driving conditions will be done with only some 50 100 psi in the combustion chamber with no justification for use of 91 94 m r 2 octane high test premium gasoline under these operating conditions a lower octane number gasoline is deemed far more appropriate under such operating conditions according to preferred embodiments of the present invention as shown in fig1 and 3 an on board system would require a duel fuel tank arrangement on a vehicle which arrangement can include either a single tank with a dividing diaphragm fig2 or two separate tanks fig1 and 3 in a particularly advantageous embodiment of the invention the tank or compartment which contains higher octane fuel is configured to have a smaller volume than the other tank or compartment as diagrammatically shown in fig2 see volumes v 1 and v 2 also one of the tanks or one of the fuel compartments in the case of a single tank with a dividing diaphragm may be advantageously equipped with a unique fill pipe configuration as shown cross section view of configurations of the fill pipes 1 and 2 in tank 2 of fig3 for example fill pipes 1 and 2 may differ in cross sectional shape or size at least at a portion which receives fuel from an external source e g from a conventional gasoline pump as shown on fig4 the fill pipes may be identical thus making manufacturing thereof more economical but have unique input.