I think you should check what would really happen. If you turbo your car, which with high boost and no engine management (altering ignition/fuel), you are seriously risking detonation and blowing your whole engine. And if mitsu finds out you turbo'd your car, there is no way in hell they are going to replace the engine. As I see it, they would be horrible business people if they replaced the engine because of the result of something you did on your own free will. I don't think I would be able to find 5 dealerships in the US that would be willing to warranty an engine that was not built for turbo but was turbo'd anyways.

 

Any kind of modification comes with some risk or side effect. For Turbo'd your car, maturity of the driver is essential. Sometimes we just want to keep pressing the 'up' button on our boost controller. It is not the turbo'd your car that Mitsubishi Motor strict about the warranty coverage, but when (IF) you did blow your engine, how did you do it (what is the caused)? Of course, if you running your stock 4g69 without proper fuel management system (E-Manage) and setting up the boost to 19psi, it will blow your engine away, however, this is not the turbocharged 4G69 faults, but the driver stupidity.