Ray Hall
Turbocharging

Turbocharger Facts
Free Software
TF Electronics
AutoSim

 

Turbocharger Facts

In the past anyone interested in turbocharing a engine would ask a turbocharger specialist for information. Now so many people are reading forums for information on turbocharging. They only come to a specialist looking for information when they get into trouble. There is so much very wrong information written on forums. To make it worst people read what is written and then quote it on other forums. It is so bad that I have have to do something.

Fact Turbocharger seals do not seal engine oil pressure
Fact Turbocharger seals are there to seal crankcase pressure.
Fact Turbocharger seals are made of steel, not rubber. They are a steel piston ring.
Fact Turbocharger seals do not fail. Bearings fail first then the seals leak.
Fact You cannot BLOW a seal, no matter what you do.
Fact You can easily damage the bearings, and then the seals will leak.
Fact Incorrectly designed oil drain = oil smoke
Fact Incorrectly designed crankcase breather = oil smoke
Fact Garrett ball bearing turbochargers all have oil restrictors internally. Normally 0.8 mm
Fact Garrett ball bearing turbochargers do not need an additional restrictor.
Fact It you have oil smoke, then you need to fix the oil drain or crankcase breather.
Fact You cannot suck the seals dry when dry sumping the oil drain.
Fact Turbocharger seals do not go hard or perish went the tubocharger is sitting on the shelf.

Oil drain sizes and design are critical. If the oil drain has a vertical fall of over 150mm (6") and then a smooth curve into the sump, then you can get away with a inside diameter of 13mm (1/2"). This is far from ideal, but will work in most cases. The best size is 19mm (3/4"). If the fall is less then 30 degrees, use 25mm (1").

Crankcase breather size is dependent on the number of cylinders. Engines with two cylinders need huge breathers. 30 to 40mm are needed. On a four cylinder engine you can use 19mm (3/4") in most cases. Catch Cans are a major cause of oil smoke. They restrict the engine breathing. If using a Catch Can, the hose and fitting sizes need to be doubled.
Boost pressure is a measurement of the pressure in the inlet manifold and not in the pressure the in the cylinder. How much of the air in the inlet manifold that gets into the cylinder is dependent on the exhaust back pressure. The exhaust back pressure is the pressure in the exhaust manifold between the engine and the turbocharger. Measuring the pressure and comparing to the boost pressure is the way to confirm the turbocharger match and exhaust manifold design is correct. For a performance road car you can achieve equal pressures at the engines peak torque rpm and around 2 psi higher exhaust pressure at maximum rpm. Race engines can achieve exhaust pressure a lot less then boost. If the pressure is two or three times the boost pressure then your setup sucks.
V6 and V8 engines need two turbochargers. Using one turbo just causes high exhaust back pressures and unnecessary stress on the engine.