Hopefully, your "poured wall" foundation has a footing, is reinforced with steel, and is healthy concrete poured in the last 30 years or newer.
Beyond that, I don't recommend trying what you want to do. Digging your crawlspace out will undermine your footings and cause your foundation walls to collapse. (any guess where you will be when this happens?) This should be professionally done, and I would recommend lifting the home, building a half wall on top of the existing foundation, and setting the home back on the new wall. Keep all living space egress requirements, head height, clearances, and codes in mind. This project should be professionally done by an architect and an experienced contractor.