The 4g63 is a mitsubishi motor that came in the turbo eclipses. The 420A is a chrylser motor that came in our cars. Notice that our engines sit on the left side of the engine bay (looking from the front of the car). 4g63 engines sit on the right side of the engine bay. In my opinion, theres no point of even trying to build up a 4g63 block. They are not in our cars, and to swap one into a nonturbo eclipse would cost thousands of dollars. Im not even gonna get into what you would have to buy to actually make a conversion possible, but its very expensive and not worth while.

Although its true that a 4g63 block is more durable and can handle plenty of boost out of the factory, the 420A engine is a good engine as well. If you want to go turbo, all you need to do is buy the turbo kit (hahn or star or custom). That will allow you to run from 6 to 10 psi, based on what stage kit you buy. Our engines will not handle more than 10psi of boost safely, because they were not designed for boost. Youd need to rebuild your bottom end (pistons, rods, etc.) so that you can handle the boost. But even at 6psi, you should be creating somewhere near 200-215 hp at the crank, which is a good number. 10psi should put you somewhere near 270hp at the crank.

Overall, dont try to swap engines, its not a worthwhile effort. Look into buying a turbo kit and redoing your bottom end, or buying a built 420A block from howell. Hope this helps.