R = 17;
l = 1.7;
ro = 0.05;
pe = 22;
dd = 7.5 10^-14;
dc = 2 10^-10;
Manipulate[ContourPlot[(3.8/R)^4  (1 + 2 (1 + delta) pe^2) - (3.8 /R)^2 8 3.14 ro (t + x pe (1 + delta)) == 0, {t, 0, 20}, {x, 0, 3}], {{delta, .3},
  0, .4}]