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Originally Posted by qroc
Turbocharging itself like your post indicates has been around for some time and I think its reasonable to assume BMW is able to pull this off without problems. Its not really a technically challenging thing in my view. Maybe add in direct injection and one becomes a tad more skeptical.
I think the design will be good but if there will problems it will be the quality of the parts they use and how they fit together. I don't get great feelings of the quality of the parts modern German cars use. Yah yah I don't have solid evidence although there have been some reliability surveys in which many German car manufacturers didn't come out high.
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It is a challenge. There is significantly higher mean effective pressure in the engine that the cylinders all have to deal with. There is also significantly higher heat both going into the engine and in the engine bay itself, so you need a robust cooling system. You need a sturdy engine block also that will not fatigue or warp, same with the heads. The turbos themselves are quite challenging because they're subject to constant acceleration and deceleration to and from 100,000 rpm or more, and handle the extremely high exhaust gas temperatures of petrol engines which can exceed 1000C. And they're expected to be reliable for the life of the car. The entire engine needs retuning as well both for performance and emissions because NA engines need different things than FI engines. The powerband needs to be smooth so that means minimal lag and zero boost surges or other unexpected phenomena. There are detonation issues to worry about also.
There are plenty of historical examples out there of what can go wrong with poorly designed turbocharged engines. Audi has a lot of recent ones. Oil gelling and huge coil pack issues on their 1.8T engines, and the 2.7TT V6 engines had poor thermal management which results in a lot of turbo failures. Even Toyota 2JZ-GTE engines from the Supra TT were known for secondary turbo failure on their sequential setup. The more complex you make an engine, the more difficult it is to bulletproof it. It's not easy by any means.