Cam advice for more torque from 340

The method 1 is to put a piece of clay on top of the piston, install the head and rotate the engine CAREFULLY by hand so that the piston compresses the clay against the valves and head. You can then slice the clay and measure the thinnest spot to see how much room there is. So the way I did it was to pull the lifters for intake and exhaust on piston #1. Mine were hydraulic lifters and disassembled with a snap ring. I filled the interior with bee bee's to simulate being pumped up with oil. I then reinstalled them. I installed and torqued down the head with gasket on that side, pushrods, rocker shaft with rockers for that piston. Put a nice long bar on the crank bolt and SLOWLY turn the engine 1 rotation. If you feel any resistance, stop. After 1 rotation disassemble and measure the clay.

Another method if you have a spring compression tool and dial indicator is to remove the springs on the intake and exhaust on the #1 piston. Go to your local hardware store and get a couple light weight springs to replace them with temporarily. Then prepare and install the lifters like method 1, pushrods and heads with gaskets like normal, and set up a dial indicator on the valve stem end. As you rotate the engine you can stop periodically and depress the valve till it touches the piston and measure the distance as you go around.

You will find the tightest clearances don't happen at top dead center. As the piston comes up with the valves closing, and as the piston drops after TDC and the valves start to open will be the tightest clearances. If you decide to install the cam advanced or retarded to change the rpm power band these clearances will change and can become much more critical. It might sound complicated but its much better than having the piston kiss the valves. There are a lot of different opinions on what is minimum clearance.