Is there a difference between RC7YC and RC9YC?

Yes, there is a difference between RC7YC and RC9YC spark plugs. The primary distinction lies in their heat range, with RC7YC being a hotter plug and RC9YC a colder one. This means the RC7YC is designed for applications where the engine operates at higher temperatures, while the RC9YC is suited for lower temperature environments, helping to prevent pre-ignition and improve performance in high-performance or modified engines. Always consult your engine's specifications to choose the appropriate spark plug for your needs.