Is it permissible to take a loan from a person who funds a project, on the condition of converting the loan into a share in the project upon its success, or securing it with the house or car upon its failure?

This form of contract is not permissible because it is an interest-bearing loan (riba) if the project succeeds. One of two options must be determined from the outset: either a guaranteed loan in which there is no profit or loss for the lender, or a partnership in which both parties bear and share in the profit and loss.