Do you have to use 89 octane fuel in a 5.7L 04 hemi?

No, you don't *have* to use 89 octane in a 2004 5.7L Hemi. The owner's manual will specify the minimum octane rating recommended for optimal performance and to prevent engine damage. While it might *accept* 89, it likely recommends a higher octane rating, such as 91 or even 93. Using a lower octane than recommended can lead to knocking (pinging), reduced power, and potentially long-term engine damage. Always consult your owner's manual for the specific fuel recommendations for your vehicle.