Restriction on 1/2" lines is less than .010 pounds per foot. On 3/16", it is roughly 2.2 pounds per foot. I can only estimate that a 1/8" line would provide over 5 pounds per foot restriction. I think that would be too much. Definately much higher than G.M. engineering originally calculated.
Are you sure you don't mean 3/8"? That is about .025 pounds per foot. I will probably install that size using steel lines.
