High octane increase MPG on VX?

[AlainB7]

I do always use 87 octane gasoline in my VX. But 2 time I use 91 octane and my MPG was better. But colt stard is not 1/4 turn. I have to hold for almost 1 second before it start.

I just put 94 octane to se if it will be better MPG.

Also, if I change my stock coil for Neuspeed Sport 1.3/4" drop, it will help on MPG?

[kamesama980]

higher octane gas is harder to ignite hence the longer cold-startup time. the economy gain probably is from increased ignition advance since it isn't getting any knocking with higher octane (knock sensor input to ecu). with a high-mileage engine this is common because of carbon deposits taking up combustion chamber space (higher compression ratio) or glowing (or both)