Below is the answer.
% ------------Given data-------------
w=[100:100:600]; % Speed
t=[-150:10:150]; % Torque
[W, T]=ndgrid(w,t);
FC= (0.000001.*(W.^2)+0.00053.*(W)+0.005+(0.05*W.*T))/1000; % Fuel consumption.
P=W.*T/1000; % Power
FC_table=griddedInterpolant(W,T,FC); %create a Lookup table
%----------------------------------------------------------
p1=(1:1:100); %create constant power vector
[W1, P1]=ndgrid(w,p1);
T1=P1./W1;% determine torque at constant power.
FC1=FC_table(W1',T1')'; %Determine fuel consumption at new torque
[c,h]=contour(W1,P1,FC1);
clabel(c,h);