welded combustion chamber is necessary if you want to extract every bit of horse power from an all motor setup. running a higher dome on a piston increases its weight. this in turn add to the reciprocating mass which rob horse power. by carefully welding and shaping the combustion chamber as to not cause any valve shroudings, you can achieve the proper compression and quench pad distance without adding excessive weight.

i got 265psi of compression on the compression tester on a b18b with topline stock style gsr pistons and welded combustion on a b18b head. this is with stock valves. getting the combustion chamber weld is pretty cheap. you can get the head milded for 25-50 bux at most machine shop. it cost me 100 bux to get the combustion chamber welded. if you get it done by a good welder, you don't have to replace the valve seats. take the head home and do some sweat equity on it. 265psi on a combustion chamber usually equate to 12:1 compression.