We have worked a lot with BMW tuning for several years - Ex. BMW e30, BMW e36, BMW e46 BMW e60 etc. That means, we have extensive experience in building the engine and the turbo kit on the engines that are located in those cars, for example. (M20, M30, M50, M52, M54, S54, etc.) We have built the engine and turbo kit from scratch, and know what is needed, so we can help you along the way with advice on building your tuning kit and purchasing tuning equipment.
The M20 engine is the first engine we have built on, everything from compressor kit, damper housings, and turbo kit. The M20 engine is very durable and can easily handle 0.7 bar charging pressure without doing anything to the engine. If you want more power, you can put ARP cylinder heads in the engine together with a reinforced cylinder head. Then you can drive with approx. 1.1 bar charging pressure. A good setup can be to use an "ETA engine" which is 2.7 liters, together with an M20B25 cylinder head. The cylinder head must be welded at the water channels as early as 400 hp. With such a setup, effects up to approx. 500 hp. If you want more power and safety, you must mount forged pistons and H-profile connecting rods, in addition, you can use an M21 oil pump which provides 30% more oil, and insert washers at the spring so the oil pressure is raised. Have made with the turbo kit below made 401 hp. (see references)
The M50 engine in the BMW e36 is used incredibly much for tuning and is a very durable engine. Like the M20 engine, it can easily withstand 0.7 bar charging pressure without touching the engine. 1.1 bar by changing the cylinder head and bolts. A really good choice is to use an engine without Vanos and it must be the original cylinder head as they are very durable.