I think that each number and letter stand for something, like what block, head, t for turbo..... I know between the 5sfe and 3sgte, the "f" and the "g" designate different heads. "f" being a non-performance head and "g" being the opposite, I am pretty sure they have different valve angles. The "s" if I remember correctly is the block, which is the same in these two engines. I would assume the the 1jzgte and 2jzgte is similar.