okey, from what I have seen there is not a lot of people who actually KNOW why stuff is made that way.
So answers, people add here so that it be like answer guide.

Okey,

Oiling on the turbo. :::::::

oiling in the turbo servs couple of purposes.
first of couse is to oil the bearings. the oil comes from top of the turbo and flows down and passes through the bearings and out.
of couse it helps for the bearing to work long life. If there would be no oil the bearing would have been eaten alife by the shaft in matter of secons.

second is for cooling. as oil passes through it takes away heat that is observed by the exaust housing and the friction in the bearings. This alows of the turbo to run cool, also alows the impeler to run cooler, making less heat. also it provides a protection. imagine runing full throtle and runing into a puddle (small or big) and some of the water gets on the turbo. On full heat and Throtle the turbo would crack in two. (becouse of the head diference and where the water touches that part cools and the whole place contracs and cracks.)

What Happens to the Oil
Well as you imagine oil passes through and gets very hot. Also it gets wiped up. like a cream. becouse if the whole rotation at high speed of the shaft. so when the oil gets in its like oil but when it exists it is like a foam.
Now comes the warnings. So its is very crutial to cool down turbo before you turn off the ignition. becouse else you would cook the oil inside to a crispy crude and ash. When its like oil and flows it is harder to cook that that the foam that is created inside. So it is crutial to let the engine idle for like 2 to 3 min after a good drive.

How Much oil passes through
well it is hard to way but most cars have a 1 to 2 galons of oil in a minute. but when engine is runing and presure rises then there passes even more oil.

more too come...................

 

Oil to the turbo and Out

well thats preaty easy, NOT.

To
well there is not lot of sicence here. usually when turboing a NA engine you put a T conector where the oil presure or sensor is. You put one exit a tube on the 90 deg bend to the turbo and the 180 deg you put the sensor back in. The sensor will work as when there be limited amout of oil to the turbo and the engine it will show you.
The line then goes the shortest rout posible. many times simply over the valve cover. You want as minimum amounts of bend as posible.
On the turboed stock engine (by manufacture) they make special exits for the turbo. specially designed. usually near the head. so that it be as simple as posible. but manufacturers are not limited to posibilities.

From
This is were it gets hairy. We know that the oil in the turbo gets wheeped out. So becouse of that we have to make the drain line Big. Oil has to be drained by the gravity. Well the reason for that is simple. It is important to NOT CREATE PRESURE IN THE TURBO. Why you might ask. Well becouse the seals wont hold presure. Most of the times the seals Dont hold oil out but air in. The exaust side is always under presure, Exaust gasses. The Inlet side, before the turbo starts to work, thyats like 3500 RMP. the engine creates a Vacuem in the system. Only at this time oil can flow from the turbo to the inlet side. After the turbo starts to create boost after 0psi it is imposible for the oil to flow from the turbo to the air.

If too create oil presure inside, the seals would not hold the presure, and would create leaks before the both presures normalize, like 2 psi of oil presure, 2 or more psi of air presure, etc....

 

Can i put in turbo on my 03 A8 L ?

 

Turbocharging
it is posible to turbo charge 99% of all engines in the world. but the biggest problem comes when you are limited by space.
turbo takes space, Fact!!!. if it is posible to put a turbo at the end of the exaust manifold and somehow reroute the air hoses and have a space for the flanges then it is posible to Turbo.
The other problem is the cost. On average, this days a single turbo instalation on a NA engine can cost from 500 dollars and up.

Steps
firts you need to find out what space avalable.
second you need to find out how deep is the valet. aka the max cost you wana spend.
third, maximum boost you wana run, on a static compresion 10:1 usually max is between 5 to 7 psi, and intercooled can be 8 psi. but still better considered right, that wrong.
fourth, calculate the right turbo, aka need to knwo avalability, price and etc....
fives, know what type of electrick system you need, aka piggy back, or stand alone, some sort of fuel and ignition control overide.
six, know where you can work, or someone that can. (need to cut and weld flanges in)
six and half, make your air system, if a dual turbo, then air ducts need to meet 180 degrees of each other.
seven, fine tune the car, start from safe aka reach and retarded ignition, work you way with your butt dyno.
eight, come back and say results.

there might be more sub stapes.

Calculations
some steps are needed to folow, first need to know how much boost needed, then a ratio calculated (boost + 14.7)/14.7 then needed to know how much air flow needed.
dipends on RPM and engine displacment. if a V6 then you half couse you run dual turbo or if you intened to run singal then you need to reotoute the second exaust to the turbo, then dont half it.
example:
2.8L V6
intened to run a dual turbo
max RPM 6000. (5050 RPM is the peak of HP so just go a step forward to have a spare space)
2.8L is 170Cubic inch lets asume that the engine is 80% eficient
lets use the graph, the 5 line from the botom is 5000RPM, so we get 200CFM
then from before we use the function and get that 5 psi of boost be (14.7+5)/14.7 = 1.34
then from second graph
density be 1.27
then
multiply the density to flow, 200CFM * 1.27 = 254CFM
now most turbo maps go in lb/min
so we multiply the CFM by 0.07
we get 17.78.
this is should be somewhere in the max. or at the end if the turbo map.
becouse we use half the requirnemt, we need that the turbo be 8.89 lb/min per turbo
more about that later.................

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You are correct, it is possible to turbo almost any engine but there is more to consider than just space and the number of turbo's. Before you even start looking for available space, you need to learn a little about your engine. Every engine has whats known as a compression ratio. Basically this is how compressed the air is in the cylinder. The problem comes when you have a high compression ratio(I.E. around 11:1 or higher). on these engines with high compression, a turbo should not be added unless the engine internals have been modified, otherwise you risk blowing your engine. Generally the compression ratio is not a problem but as the years have advanced the compression ratio's of cars have gotten higher. I don't think there are to many audi's with extremly high compression but i would check before you go bolting on things. My 2000 a4 has a compression ratio of 9.5:1, low enough to sustain a turbo, the V6 model is at 10.3:1 still safe enough to run a turbo.


P.S. Your compression ratio also determines the size of the turbo you can use before internal modification is needed.

 

Your A8 has a compression ratio of 11:1 kinda high. If you do put one I wouldn't run high boost.

 

right, you will be able to run like 3 to 5 psi non intercooled.