To start, I would back off timing 2 degrees for every 50 HP supplied by the NOS system. If no knock, then step up one and check. Play it safe with this stuff. If you're already one step colder on the plugs, you should be OK with a 50 shot. Any higher, start watching the ground electrode for overheating. Cutting back the ground electrode should be a 'must do' procedure for any nitrous setup. If anything gets you in trouble fast, it will be your spark plugs. Watch them very carefully. Learn to read them. You should strongly consider going to a regular nose style spark plug with a back cut side electrode. I would recommend some type of fogger to get the best mix of the nitrous gas and the extra fuel. The jet of nitrous can do a real good job of breaking up the fuel into very small droplets. You'll get less fuel drop out that way. Make sure the fuel jet size of the nitrous system is properly sized for the fuel pressure you'll be using. I think someone posted a chart on another thread. It may be the one referred to earlier in this thread.