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Chapter 3 - Turbocharger Systems and Components
So what makes up a complete turbo system? In this chapter, we will take a look at all of the basic turbocharging components and explain what part each one plays in creating and controlling boost and engine management.
The Turbocharger (in a nutshell)
The turbocharger is the heart of the system. It is comprised of a turbine and a compressor. The turbine is spooled by the spent exhaust energy that is expelled from the cylinders. The exhaust energy spins the turbine to extreme RPMs creating terrific potential energy.
Connected to the turbine via a shaft, is the compressor. It is the compressor's job to draw in fresh air and force feed it into the engine's intake. The engine's ability to create power increases by increasing its volumetric efficiency.
Cutaway of a turbocharger showing the turbine (red side) and compressor (blue side).
It is the wastegate's job to control the turbine's speed, thus preventing overspin and overboost. The wastegate is placed before the turbine inlet in the exhaust system, and is referenced to a boost source. When boost reaches the wastegate's designed operating pressure, a valve is opened, redirecting exhaust energy away from the turbine. By redirecting energy away from the turbine, it is not allowed to increase its speed, and therefore prevents the compressor from increasing boost pressure.
Once the boost pressure has fallen below the wastegate's operating pressure, the valve is closed allowing all of the exhaust's energy to spin the turbine.
Inside of the wastegate, there is a spring that is calibrated to control the pressure at which the valve opens. Some wastegates are adjustable. Others have interchangeable pre-set springs. The springs are rated in BAR (14.5 psi). So a wastegate set at 1 bar will open just before the boost reaches 14.5 psi gauge pressure. A .25 bar spring will open and keep boost at 3.625 psig (14.5 x .25).Keep this is mind when you purchase your wastegate(s).
Also remember that a wastegate can be controlled to open at a higher boost pressure by the use of a boost controller. For example, if you purchased a wastegate with a .25 bar spring and later you decide that you want 5 psig of boost, you can attach a boost controller to the wastegate to delay the opening of the valve until 5 psig is reached. More on boost controllers later.
The wastegate should be referenced from a boost source. Some turbochargers have a port on the compressor for connecting a hose to the wastegate reference port. You can also pick up the reference from the charge tube by tapping and placing a hose barb in the charge tube. If you are installing a twin turbo system, you will need two wastegates.
A TiAL wastegate.
Blow Off/Bypass Valve
The blowoff valve (BOV) prevents pressure build up the charge pipe when the throttle blade is closed after a positive boost condition.
Let’s imagine that a turbocharger is supplying 5 psig under a full throttle condition. The throttle blade is open, and boost is being supplied to the engine, while exhaust energy is spinning the turbo.
Now imagine that the throttle blade is suddenly slammed shut as it would while shifting a manual transmission equipped vehicle. Even though the exhaust energy has been reduced to the turbo, it still continues to spin at a high rate of speed supplying boost. The problem is that the throttle blade is shut, and the boost pressure cannot enter the manifold. Therefore, pressure builds in the charge pipe between the throttle blade and the turbo's compressor.
Two things can happen at this point, either the pressure builds until a hose clamp blows off, and/or the pressure tries to back itself through the compressor blades. Both cases are not good. Damage will occur to the turbocharger over time if backflow continues to release though the compressor, not to mention performance loss from backpressure slowing the turbo, causing lag time to re-spool between shifts.
The solution to these problems is a BOV. The BOV will open when a vacuum is sensed in the manifold, and positive pressure exists in the charge pipe. Excess boost is quickly bled off into the atmosphere preventing backflow through the compressor, and/or hose connectors popping off. You can hear a BOV when it is activated on a turbocharged vehicle. It is that neat psssssh sound heard during shifting.
The turbocharger will also stay spooled between shifts with a BOV, preventing turbo lag and increasing performance.
On some forced induction applications, you are able to blow-through the MAF. Some engines however, require drawing through the MAF. A bit of searching on the internet will let you know if you can use a blow-through type of system, or need to draw-trhough your MAF.
On a draw-though system, the MAF is placed on the inducer side of the tubocharger's compressor. Air entering the charge pipe after the turbo is metered by the MAF. On draw-through systems, a BOV would dump metered air into the atmosphere, causing an incorrect air fuel ratio.
The solution to this problem is a called bypass valve. The bypass valve acts like a BOV, but dumps back into the intake pipe between the MAF and compressor, keeping metered air in the system and maintaining a correct AFR.
The BOV can be mounted before or after the intercooler, but always before the MAF.
Blow-off valve mounting location.
Boost Reference Location
Picking up a boost/vacuum reference point on an engine can be done at any available vacuum port on the intake manifold. On cars that are equipped with brake boosters, a vacuum source can be picked up at the brake booster vacuum hose. A nylon Tee can be placed inline with the hose and can be used as a reference for the boost gauge, BOV, alky injection switch or any other device that needs to be boost or vacuum referenced.
Boost/vacuum reference from the brake booster hose on a Z28.
If you do not have an adjustable wastegate, or like the convenience of dialing your boost from the cockpit or other easily accessible area, a boost controller is what you need.
A boost controller plumbs inline with your wastegate and allows you to increase boost above the wategate's maximum opening pressure. For example, if you have a .25 bar spring in your wastegate, a boost controller will allow you to dial in boost pressures above .25 bar, but not below that.
Manual Boost Controllers
The simplest and least expensive type of boost controller is the manual type. It is very easy to install and operate. Simply plumb it between the wastegate’s boost reference and the wastegate and you’re done. A knob or dial on the controller lets you turn up the boost as needed.
The manual boost controller works by tricking the wastegate into thinking that the boost pressure is actually lower than it really is. It does this by creating a controlled leak in the boost reference line. The larger the controlled leak, the lower the wastegate boost reference is. One popular manual controller is the Perrin Performance manual boost controller. It retails for about $80 and claims to decrease spool time.
Perrin Performance manual boost controller.
Electronic Boost Controllers
Electronic boost controllers use a stepper motor to control boost pressure. The advantage here is that the wastegate does not slowly open like during normal operation. It opens quickly as the target boost pressure is reached thus drastically reducing turbo spool time.
Electronic boost controllers allow you to set different boost levels that can be changed with the touch of a button. You can select different boost setting for street, track, pump gas, race fuel etc. Some EBCs even allow you to select different boost levels for each gear like the E-Boost2 from TurboSmart.
The Greddy PRofec-B is an easy to use electronic boost controller that allows you to control boost on the fly. Also look into EBCs from A’PEXi, Blitz and HKS.
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