You need something with a map sensor (MSD 6BTM) or something programmable (MSD 6AL-2 programmable) so that you can reference your timing to manifold pressure. That allows you to keep the timing in the engine for cruising (fuel mileage and temperature) and pull timing when boost comes in. The 6btm is manual and easy to set. The 6al-2 uses MSDs software and is pretty easy to navigate and understand.