The MSD's come with the wrong springs installed--why who knows but..take any MSD and install the black stop bushing and one of the light blue springs along with one of the lightest springs--this will give you the initial advance desired on most performance engines and limit the mechanical --will work great in 90 % of hot rod builds--ALWAYS spray the MSD reluctor with WD40 and them blow it off with air hose--they are some crazy kind of metal that WILL corode in a massive way sooner or later--this tip helps keep that at bay--ask anyone that has had one over a year or so and they can describe the horrible orange crust that will stop one in its tracks--I would go Pro billet with no vacuum--