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      05-10-2006, 09:05 AM   #48
qroc
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Drives: 2007 335i
Join Date: Apr 2006
Location: Bristow, VA

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Quote:
Originally Posted by SteVTEC
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.
Coil packs don't necessarily have anything to do with turbocharging afaik.

Hehe, having owned and dealt with modifying heaviliy a 911 turbo I hear you. Its more complex than na cars but I don't consider it a particular challenge for BMW to do turbocharging right. There is industry data on this since the 70s yes?

But given how common turbo charged cars are nowadays, how old the technology is, how they are gaining popularity, and how tbh I can't think of any recent turbo cars which had spectactular design failures (I think of the reliability of Subaru's turbocharged cars in particular) I feel pretty good about BMWs ability to pull it off. The direct injection part is in my view a cause for concern if any, as well as how damn complicated the engine is (just read the Edmunds thing re: the water pump etc).
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