PHP Code:
new Float:velocity[3];
entity_get_vector(id, EV_VEC_velocity, velocity);
new Float:dir[3];
xs_vec_copy(velocity, dir);
dir[2] = 0.0;
xs_vec_normalize(dir, dir);
xs_vec_mul_scalar(dir, 250.0, dir);
xs_vec_add(velocity, dir, velocity);
velocity[2] = 250.0;