Another note...IAV probably is in this century, if they took a current engine and tweaked it, and simulated all the crap on a computer to see what would happen(and got that bit right) then the only bit left is to physically tweak some of the already proven engines and actually test them to see if they behave.
Not anywhere near the expense of starting with an idea and some metal stock.
Not anywhere near the expense of starting with an idea and some metal stock.