i think unless youve got a motor specifically designed for super (ie Mitsi Evo etc) its pretty much a waste of time. the experts say that it also takes more than a full tank of fuel for the ECU to sort itself out. Mixed reg and super defeats the purpose. The only time ive noticed a difference is when driving my old Subaru Chavwagon. It specified Super, but once or twice i was forced to fill with regular and it ran like a pig..JDM cars will destroy their engines on regular.