I don't think you would be satisfied at all with a home-brew turbo installation. In the first place, engines that are turbocharged have fairly low compression (6 - 1 or so) so the turbo can ram more air/fuel charge into the combustion chamber to make more power. If you try to turbo your engine without changing the pistons to lower compression ones (are they even available?), all you will do is cause detonation, which will destroy your engine in short order. I have had some experience with turbocharged engines and even with adding a turbo (but only on an off-road racing vehicle), and I can say from experience that you will be sorry you ever tried it, if you do. The turbo requires an UNIMPEDED return flow to the pan for the used oil. (minimum 7/16" pipe, 1/2" is better.) The oil cools the bearing, and the return oil is quite hot. Usually turbos require a full flow on the supply side to the bearing, which is actually an aluminum bushing on most turbos - the shaft just "floats" in an oil bath. (read "larger capacity oil pump") There really isn't much of an oil seal on the exhaust side of the shaft - there is a sealing ring, but it isn't up to handling any pressure. On the intake side there is a seal, but it will blow out if the oil return is impeded. The engine's advance curve must be radically altered to allow the varying combustion pressures not to detonate - I doubt if the knock sensor setup could handle it. In my opinion, a bigger engine would be much better and last much, much longer.
1983 300D/4.3L V6