Do Modern Hemi Engines Need Premium Gas?

With the dizzying array of options at some gas pumps, it can be hard to decide if you should use premium gas in your car or take the less expensive option. Owners of vehicles equipped with modern Hemi engines face the same dilemma. With features like dual spark plugs in each cylinder, Hemi drivers might think they need to reach for the highest grade of gasoline when fueling up. But the real answer is: it depends.

The modern third-generation Hemi made its debut in the 2003 Dodge Ram pickup truck. During the 23 years that have elapsed since that time, three other Gen-III Hemi variants have powered various vehicles under the Stellantis banner. The Hemi has also been discontinued and quickly reinstated as if nothing happened. With such a long and sordid history, it's understandable that some modern Hemi engines require premium gas while others can get by on lower-octane varieties.

Automakers have included vehicle owner's manuals throughout the history of automobiles for one good reason: to answer people's questions about the car they're driving. While there could be a sticker on the inside of your fuel door dictating the octane level required, the most reliable information about your car is found in the owner's manual it came with — or an online copy if you don't have the original.

For example, the owner's manual for a 5.7 Hemi-powered 2010 Ram 1500 recommends against the use of premium gasoline since "it will not provide any benefit over regular gasoline in these engines." Instead, it advises using 89 octane, a mid-grade gasoline, for "optimum performance," although it says the engine delivers "satisfactory fuel economy and performance when using high quality unleaded gasoline having an octane range of 87 to 89."

On the other hand, the 5.7 Hemi found in 2023 Dodge Challengers equipped with manual transmissions should always use premium gas with octane ratings of 91 or higher, according to the owner's manual. Interestingly, the same car with the 5.7 Hemi paired with an automatic transmission has the same 87 to 89 octane recommendation as the 2010 Ram 1500's 5.7 Hemi.