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There are some interesting choices in routing. The air box is in one corner and wraps all the way across the engine bay to get to the turbo. Maybe they needed that length of intake pipe for some resonance tuning or something.
There is a whole lot of stuff crammed into this area. The black plastic duct on the left goes from the air box in the corner to the turbo compressor inlet. Those two rubber hoses with protective sheath around them are probably for the compressor bypass valve getting recirculated and the breather for the PV system. Running over the turbine housing heat shield is the compressor discharge pipe, which is not what I would call an ideal placement. The compressor discharge pipe wraps around the back side of the engine. An A/C line also goes very near the heat shield for the turbine housing and has some heat shielding on it.
Stuffed way down there underneath all the lines is the air-to-water intercooler.So there you have it, even the Japanese are going back to boost. With the addition of turbochargers for boost, all of the OEMs are now playing the game of trying to maximize throttle response and low-end torque. The German makes have their twin-turbo V8s (BMW, Audi, Merc) with the turbos placed in the middle of the V to allow for twin-scroll turbo setups for maximum response. To make V6s, they cut off a row of cylinders and left the turbos in the middle of the V. Making a V6 from scratch, Nissan and GM decided to place the turbos on the outside of the V (you cannot use twin-scroll turbos with only three cylinders) and use air-to-water intercoolers to create very short air flow paths for maximum response. Mazda is using some tricky variable turbine valves to get faster response and spool-up.
The whole idea in improving turbo response is to get more torque to the wheels faster. Volvo decided to do a compound setup adding a supercharger to the turbocharger to eliminate lag. BMW decided to go another route in getting instant torque to the wheels and that was with an electric motor in their plug-in hybrid setup. The next things I expect to see are e-boosters and e-turbos. An e-booster is actually in production already (or very soon to be) on an Audi diesel and it’s an electrically driven centrifugal compressor. So it creates instant boost until the turbocharger spools up. E-turbos have an electric motor integrated and that technology is being proven out right now in Formula 1. When will that make it to the street? Probably for not a while as it requires high voltage systems and batteries. The path BMW has taken with the turbocharged gasoline engine with a plug-in hybrid powertrain is the right architecture for an e-turbo. When/if that technology makes it to a street car, there will be plenty of guys in suits under bright lights at auto shows checking it out.
