Copyright by Goodheart-Willcox Co., Inc.
346 Auto Engine Repair
A waste gate limits the maximum boost pressure
developed by the turbocharger. Without a waste gate, the
turbo could produce too much pressure in the combustion
chambers.
A turbocharger intercooler is an air-to-air or air-to-liquid
heat exchanger that cools the air entering the engine. It is
a radiator-like device mounted at the pressure outlet of the
turbocharger.
A supercharger normally consists of the housing, rotors,
timing gears, extension housing, and drive pulley. A super-
charger bypass valve may also be used to improve engine
efficiency by only providing maximum boost when needed.
Most superchargers are direct drive. However, some
have an electromagnetic clutch that allows the supercharger
to be engaged and disengaged.
When the accelerator pedal is pushed to the floor for
passing or getting up to highway speed, the supercharger
spins faster to provide more boost. Engine power is instantly
increased. Most superchargers used on production vehicles
provide 4 psi to 10 psi (30 kPa to 70 kPa) of boost.
A supercharger intercooler removes heat from the
compressed air before it enters the engine. A supercharger
intercooler system consists of the intercooler, intercooler
coolant, intercooler lines, intercooler pump, and intercooler
radiator.
Supercharger service may be required after extended
use. Usually, a supercharger will fail because of worn
bearings or damage to the impeller and housing.
When diagnosing problems with the supercharger
system, inspect the unit for obvious problems first. Some
supercharger noise or whine is normal. A rattling noise
from the supercharger indicates rotor bearing failure and
mechanical contact between the spinning rotors and the
inside of the supercharger housing. A knocking noise
indicates possible drive gear teeth breakage.
When a supercharged engine fails to generate proper
boost pressure, it is often due to a broken or slipping
drive belt, an inoperative electromagnetic drive pulley
mechanism, an inoperative pressure bypass valve system,
physical wear or damage inside the supercharger, or a
badly clogged air filter or an obstruction in the air intake.
Overboost can be caused by a bypass valve stuck closed,
electronic control problem, or engine modification.
Problems with the intercooler system are similar to
the problems that develop in the engine cooling system.
During service, check the level and condition of the cool-
ant in the intercooler reservoir. Pressure test the system as
you would the engine cooling system.
Superchargers are not normally serviced in the field
and are simply replaced as a unit. However, seal kits are
available that typically include the gaskets, oil seals, and
special oil for the supercharger. The belt is also a normal
wear item that requires periodic replacement.
Review Questions—Chapter 16
Answer the following questions using the information
provided in this chapter.
1. Define normal aspiration.
2. What is the basic purpose of turbocharging or
supercharging?
3. List four engine modifications normally found on
turbocharged or supercharged engines.
4. List the six parts of a turbocharger.
5. Describe the operation of a turbocharger.
6. _____ is the short delay before the turbo develops
sufficient boost.
7. What is the function of a waste gate?
8. Why is an intercooler needed on turbocharged and
supercharged engines?
9. Describe the basic operation of a sequential
turbocharger system.
10. Minor problems, such as a bad waste gate control dia-
phragm, leaking seals or hoses, or damaged housings,
can be done in the shop. Otherwise, the turbocharger
must be _____.
11. List the five basic parts of a supercharger.
12. What is the purpose of a supercharger bypass valve?
13. A supercharger intercooler:
(A) cools the air coming into the air inlet.
(B) is typically an air-to-air heat exchanger.
(C) cools the air coming out of the supercharger.
(D) results in a cooler, less dense charge of air
entering the intake manifold.
14. List four problems that may be indicated by low
supercharger boost pressure.
15. List three problems that may result in overboost.