Only if your car was designed for it (see your owner's manual) or if you've advanced the timing on a classic car, or if your engine is knocking (unleaded gasoline has a slightly lower octane rating than leaded, so some pre-1974 cars may need midgrade fuel). Many high-octane gasolines have a low driveability index, which can cause long cold start times, warm-up sags, hesitations, and driveway die outs. All gasolines sold in the US meet the same standards for detergent. SRT engines and most turbos use premium fuel. The 3.5 V6 and 5.7 Hemi required midgrade (89 octane) and the 392/6.4 Hemi required premium. Most other 'Mopar' engines of the 1980s through today take regular fuel.