From Dana at fj40dana@hotmail.com:

Here is an interesting thread from the DTLC all about Turbos that I hope can provide some reasonably in depth information:

Listers, I contacted Berrima Diesel in Aus, and they sent me some very 
interesting diesel info, in the form of several attachments.  Here is one, 
I'll send the others in separate posts.  Please note the comment about 
aneroids.

Dana
 

from Berrima Diesel:

Tech Sheet
'Turbo Myths and Facts'
Myth-  This turbo is totally oil cooled as water cooling is troublesome.
Fact- There is no such thing as an oil cooled turbo charger!! All turbo 
chargers are oil fed due to the fact that they all have bearings that need 
lubricating. Turbocharger units are either water-cooled or not! Full Stop!! 
Unfortunately most aftermarket turbo kit manufacturers specify a non-water 
cooled or use the water-cooled turbo, but leave the water-cooling 
disconnected. All for a cost sake!! As usual, the excuses used leave the 
customer confused! Water cooling came about to increase the durability and 
life expectancy of a turbo unit. This is visible if we look at factory turbo 
charged 4WD's. They nearly all use water-cooling.

Myth- The engine will run a much lower engine temperature if it is 
Intercooled.
Fact- A diesel engine compresses the cylinder air charge to approx. 500PSI. 
This is done as the air needs to be red hot so that when the diesel fuel is 
injected, it immediately ignites. As we can see, hot air for a diesel is not 
a problem. Intercoolers are generally sold with the myth of running cooler 
denser air and lower temperatures, whilst dramatically increasing power. The 
temperature part would be true only if the increased power part was left 
out. To get the increase in power sold with an Intercooler we now have to 
increase the fuel loading higher. As I always say, more fuel makes more 
power with the offset of more heat.
Let's now look at the other problems associated with Intercooling. Over 
fuelling and hungry for power is the biggest one which definitely cooks 
engines. The most common of all though is radiator air flow restriction. The 
radiator needs cool air to cool the hot engine coolant. Generally up front 
we have a bullbar, driving lights, bug screens (all diverting small amounts 
of air flow),  we then have the introduced Intercooler dumping hot air over 
the air conditioning condenser (most air conditioners shut off  if the 
engine coolant starts to get too hot to try and aid in keeping cool air 
going to the radiator) which is dumping now extremely hot air over the  poor 
old radiator. The radiator is now getting the leftovers and is expected to 
cool the power enhanced, hard working engine. This problem gets worse as the 
ambient air temperature increases.
So... an Intercooler added to a turbo system may not run cooler.

Myth- Particular companies don't increase the engine output too much ,when 
turbocharging, so as to keep long engine life.
Fact- This comment is alarmist! It is impossible to gauge the original life 
of a diesel engine let alone one that is now turbo charged. If a turbo 
system is set up correctly, it will have no effect on engine life. Here at 
Berrima, we suggest that engine life could be possibly lengthened, with the 
install of a correctly set up turbo system, due to the fact that it is now 
running with increased efficiency which can help with reducing soot build up 
in engine oil and around piston rings etc! We see vehicles that we turbo 
charged many years ago coming back with 500000km on the engine and no sign 
of it wearing out. Diesels last if correctly maintained!
 

Myth- You must fit a Fuel pump aneroid (fuel compensator) when you fit a 
turbo as it will run better and give you more power.
Fact- For starters the addition of an aneroid to your injection pump will 
cost upwards of $800-$1000 on top of a turbo system. It is specifically 
designed as a pollution control device and is fitted only to factory turbo 
diesel. Unfortunately in aftermarket turbo fitment, an aneroid can be used 
as a device to mask over fuelling and over powering the engine.

Myth- Some companies promote large, low boost, cool running turbo units!!!
Fact- Get real! It's simple physics. Pressure and volume are relative to 
each other. A turbo running higher boost gets higher volumes of air to an 
engine than the one running lower boost. The higher the boost the more air 
volume! A turbo is only an air supply device. Boost pressures used in turbo 
charging are relatively low and don't generate much heat if any. If we kept 
compressing the air to a couple of hundred PSI though, air would soon heat 
up. It still stands that fuel makes the heat in the equation!! Loads of fuel 
means loads of heat. A correctly matched turbo spins up fast so as to keep a 
nice lean mixture down low and to get a torque increase early in the rev 
range(a lean mixture is cool and clean in a diesel!!). As we know, diesel 
engines produce maximum torque at low engine revs so we need a turbo to be 
at maximum boost at those low engine revs. What's happened now to the 'large 
low revving turbo'? Not much, until the engine revs get up high. Too late 
for the boost to arrive at high revs! In fact if the boost is kept low and 
the turbo spins up slowly, the fuel and air mixture can be quite rich in the 
low to mid working range of the engine. Rich means heat in a diesel. That's 
why using a large 'cool' turbo charger is a fallacy! With the high revving 
diesels of today, a turbo needs to boost early and hold the boost through 
the large rev range. The variation in a 4WD diesel rev range can be 4000RPM 
between idle and redline.

Myth- Use the old manifold and just adapt the turbo to it.
Fact- This is a real worry. The original exhaust manifold is not designed to 
have the weight of a turbo unit swinging off it or the increased 
backpressure that a turbo creates in the system. Having a specifically 
designed new exhaust manifold for the turbo to bolt to is only common sense. 
A specific turbo exhaust manifold is internally split for cylinders 1,2,3 
from 4,5,6. This is specific for exhaust flow and increased low speed 
torque.

Myth- The turbo must be mounted high up in the engine bay so as not to crack 
in water.
Fact- High mounting in certain engine bays can lead to excessive engine bay 
temperature. We have seen some funny cases! The most common is systems using 
a high mount position, for the turbo, in the Nissan Patrol. We have seen  
some melted glove boxes, cooked batteries and even paint damage to bonnets. 
As far as water crossings cracking turbo housings go, I don't know who would 
drive at full speed long enough to get the turbo orange hot and then plough 
into a river deep enough to fill the engine bay. You can imagine the picture 
let alone the splash! The castings are strong enough to withstand splashing 
and possible immersion ,whilst hot, under most conditions.

Myth-You need a high flow foam filter when turbo charging.
Fact- If you don't know our stance on this subject just ask! Ask the turbo 
reconditioning industry how much foam they find behind compressor wheels in 
turbo chargers when they are being rebuilt!