i am trying to do as much research as possiable to make a good reliable and strong motor hopefully the good feedback keeps comeing ive been reading about ls6 valves and springs/. anyone know anything about that
1. L31 castings are thin-wall and crack-prone. You may have to magnaflux several sets of them to find two valid players.
2. Yes, you can gain more lift with different springs, but that doesn't address the O.D. of the valve guide. Without cutting the guides, you're still limited to single springs with no damper and stock seals. Try running a roller cam with small diameter single springs. Good luck. Best way is to shorten the guide and reduce the diameter of the guide. Then you can use the correct springs with the correct diameter and dampers for a hydraulic roller cam.
3. Rocker studs are pressed-in and will not tolerate more than about 260 lbs over the nose until they begin pulling out of the heads. You can fix this by drilling and pinning the stock studs or pulling them out, milling the stud pedestal area and tapping for screw-in studs. If you don't mill the heads at the stud area, the screw-in studs will sit too high and you won't have enough thread to adjust the valves.
4. The holes where the pushrods come up through the heads will have to be clearanced.
By the time you get all this done, you will have more invested in these heads than they are worth and they still won't perform as well as a dedicated aftermarket head.
Look at these #12410-02 assembled cast iron heads from Racing Head Service......
Pro Torker Assembled Cylinder Head Racing Head Service (RHS) 12410-02 - Pace Performance Parts
A complete set of heads with hydraulic roller springs, screw-in studs and guide plates, $958 for the set and they'll flow better than the L31 Vortecs and they won't crack as easily. They'll easily make 400 hp and 450 ft/lbs of torque with a well-matched set of components.
I can guarantee you'll have more than that invested in a set of L31 heads by the time you upgrade them to the level of these RHS heads.
