A good place to start. keep in mind that a lot of these heat range recommendations are for racing where there is a lot of heat. So don’t be surprised if the recommended plug is a bit cold on the street. This is just a cut and try exercise to dial it in. I have a large grungy spark plug collection, I keep ‘em for protecting the spark plug threads when painting heads.I looked up the FR5 and they are exactly what AFR calls for.