Depends on what you got. Stock or built?

If it is stock I would start somewhere around 8 to 10 BTDC initial and see if there is any detonation. Back it up a little if there is pinging, advance to just before detonation. Or if you dont have a light you can hook up a vac. gauge to manifold and advance just until max vac. is achieved. I dont really like this way but if you have no light that would get you close. Just make sure you eliminate any pinging\detonation.