Using a higher octane gas than needed is a waste of money. Lower octane gas ignites at a lower temperature than hi-test. In high compression engines low octane gas will ignite before the sparkplug fires causing a pinging sound. If your owners manual does not recomend high octane gas and your car does not have a pinging sound coming from the engine when under strain stick to regular. Twenty years ago when most cars had carborators the gas companies put additives only in their premium gasolines which were needed to keep the fuel injectors clean. Therefore, if you had a fuel injected car the recomendation was to use hi-test whether you needed the higher octane or not. Today all major brands put fuel injection additives in all their grades of fuel.