Stp does contain zddp (zinc) where Lucas doesn't claim it has. A very valuable anti wear additive to prevent metal to metal scuffing as a last resort. Both Amsoil and Mobil 1 have reduced this amount over the years. Very important in flat tappet camshafts among other areas. Most of the modern auto oils have eliminated zddp and gone to other additives for the same task. However, flat tappet engines will destroy themselves using it, so the choice of oils is important .For our engines, the choices of good motorcycle blend oils works just fine. Yes mc oils are a bit different then auto blends. For us, it's which mc oil withstands sheer the best, due to the trans, which has a nasty habit of chopping up the multi grade molecules and thinning the viscosity. Viscosity break down in the form of fuel dilution is another area of concern with these engines. Stock tune, no problem but some of the tunes out there are over rich , that can cause problems.