Can the original GX390 piston be safe if revved to 6000 6500, has the billet flywheel, rod and
a 330 lift 246* champion rockers, manton push rods, do not know what springs I should use,
I got 32 singles and 55 double springs.
There are 3 distinct and different "stock" 390 pistons. Tier 3 (UT2) 1310X-Z5T-800 , Tier 3 (UT1) 1310X-Z5T-000, and Tier 2 1310X-ZF6-W00. All 3 come in std, .010, .020, .030 sizes. First 2 have thin 1mm thick rings. Last one has thick 1.6mm rings. The first one listed is called the "short skirt" piston. Much much lighter than the other two. Last 2 seem identical except for ring thickness, both very heavy. Dish is very similar in all 3. If you plan on turning high rpms, the lighter the better (first one). Much less stress on parts. Also remember that Honda refers to the .010 over piston as .25 over, the .020 over is refered to as .50 over and .030 over is .75 over. Most use "inches" and Honda uses millimeters. Good luck