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Looking for info on the new N20 turbos...

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I was thinking of adding a turbo(s) to the M10 at some point (MS, etc.). So I try hunting down some info on what two smaller(?) turbos were used on the new BMW N20 (better boost at lower rpms?). Still haven't found the details on the turbos but I did run across this cool video:

...I'm probably late to the realization that one day I might be taking apart motors that were put mostly together by robots.

Any one have any info on the smaller turbo specs?

/Martin

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5.3.1.�Function�of�TwinScroll�exhaust�turbocharger

The�designation�TwinScroll�denotes�an�exhaust�turbocharger�with�a�twin-scroll�turbine�housing.�The

exhaust�gas�from�two�cylinders�in�each�case�is�routed�separately�to�the�turbine.�In�the�N20�engine�(as

is�usual�in�4-cylinder�engines)�cylinders�1�and�4�and�cylinders�2�and�3�are�brought�together�to�form�two

ports�each�feeding�one�scroll.�This�results�in�pulse�charging�which�is�used�to�greater�effect.

Pressure�and�pulse�charging

Two�principles�of�forced�induction�are�used�in�engines�with�exhaust�turbochargers�–�pressure�and

pulse�charging.�Pressure�charging�means�that�the�pressure�ahead�of�the�turbine�is�approximately

constant.�The�energy�which�drives�the�exhaust�turbocharger�is�obtained�from�the�pressure�difference

before�and�after�the�turbine.

In�the�case�of�pulse�charging,�the�pressure�before�the�turbine�is�high-speed�and�greatly�fluctuating,�or

pulsating�by�the�discharge�of�the�exhaust�gas�from�the�combustion�chamber.�The�pressure�increase

results�in�a�pressure�wave�which�strikes�the�turbine.�In�this�case,�the�kinetic�energy�of�the�exhaust�gas

is�used,�whereby�the�pressure�waves�drive�the�turbocharger.

Pulse�charging�provides�for�a�fast�response�by�the�turbocharger,�especially�at�low�speeds,�because

pulsation�is�at�its�strongest�here,�whereas�in�the�case�of�pressure�charging�the�pressure�difference

between�before�and�after�the�turbine�is�still�low.

In�actual�fact,�both�principles�are�always�used�in�exhaust�turbochargers�in�passenger�car�engines.�The

proportion�of�pulse�charging�is�higher�or�lower,�depending�on�the�size�factors,�the�exhaust�port�guides

and�the�number�of�cylinders.

Dependence�on�the�number�of�cylinders

In�a�single-cylinder�engine�there�is�an�exhaust�cycle�every�two�revolutions�of�the�crankshaft.

Theoretically,�exhaust�gas�is�therefore�discharged�for�180°�every�720°�crank�angle.�The�graphic�below

shows�in�highly�simplified�form�the�pressure�conditions�before�the�exhaust�turbocharger�in�a�singlecylinder

�engine.

TurboTwinScroll_P0017850.jpg

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