Clip contour with envelope

I'd need to clip a contour map with an envelope. As straightforward as possible: I would like to work with contour plots for engine characteristic map (X,Y,Z are scattered data) So, I use:

F = scatteredInterpolant(X,Y,Z,'linear','none');
[X_grid, Y_grid]= meshgrid(X_array, Y_array);
Z_map = F(X_grid,Y_grid);

Now I'd like to use extrapolation function, but plot the map with "contour(f)" and clip it with an envelope, that can be e.g. the full load curve (if X is engine speed, Y Bmep). What I ask is whether is there an envelope function and whether a contour(f) can be clipped with this envelope.

[sst]

Similar question from my end. Is there a way to do this?