what sparkplugs can i use

Pat each application is different. I believe the rule of thumb for power tuning is to start out at .035" and open them up .010" at a time until it misfires then close them back up .005" but I've noticed that if I do that they don't last real long on a street car that gets drove a lot so I open them until it misfires then close them back up .010". If it's a race car that gets the plugs pulled and checked a lot the old rule of thumb should help you make the most power.