Muscle Mustangs & Fast Fords
Turbos & Superchargers - Forced Introduction
A breakdown of turbos and superchargers that everyone can understand.
To relieve excess boost, a bypass valve is normally located in the outlet tubing. Using engine vacuum as a gauge, the bypass valve bleeds off excess boost pressure to the low-pressure side of the system before the supercharger inlet.
The operation of a centrifugal supercharger creates less heat than that of a positive displacement supercharger. “Centrifugal superchargers produce significantly cooler air-charge temperatures due to their design and overall advantages in efficiently compressing air,” says Lacina.
Centrifugal superchargers have been a staple of the Mustang aftermarket since the early ’90s, before turbo kits or positive displacement superchargers were widely available. Companies like Vortech, Paxton, and ProCharger have been at the forefront of technology, and all provide a wide array of kits for almost every late-model Mustang application.
TurbosTurbochargers, or most commonly turbos, are air compressors driven by the otherwise-wasted energy stored in exhaust gasses of an internal combustion engine. In simpler terms, turbos are driven by the exhaust flow.
A turbo basically consists of a turbine wheel, a compressor wheel, and a center housing. The exhaust-driven turbine converts heat and pressure into rotational force by applying pressure on the impeller and turbine shaft, causing it to spin. The turbine shaft is connected directly to the compressor through the center housing (which houses the bearings). On the other end of the turbine shaft is the compressor wheel. Like a centrifugal supercharger, the compressor wheel draws inlet air through a snail-shell-shaped housing (compressor housing) and to the intake system of the engine.
Often oiled and cooled by engine oil, turbochargers can spin up to 100,000 to 150,000 rpm. This requires solid engineering when developing bearings, housings, and turbine and compressor wheels. The main turbocharger manufacturers are Garrett Turbo, Borg-Warner, Precision, Turbonetics, and Master Power. Typically, the larger the inducer diameter (measured tip to tip in millimeters on the induction side of the compressor wheel), the more potential the turbo has to create power.
As important, though, are the other components of a turbocharger system that allow it to work. Also required are hot piping (exhaust side), a wastegate, cold piping (inlet side), and a blow-off valve. Unlike a supercharger system, turbocharger systems often require significant (and perhaps complicated) piping, and either welds or clamps to seal the tubes, preventing either exhaust gases or compressed air from leaking out.
Hot piping is what routes the exhaust gases to the turbine housing. Often necessary, or preferred, is the manufacture or modification of exhaust manifolds. Because a turbo/turbos are typically mounted near the front of the engine (to take advantage of cool, fresh air from outside the engine bay), most turbo exhaust manifolds point forward.
In the hot piping before reaching the turbo housing is the wastegate. It bleeds off excess exhaust gases into the atmosphere or the exhaust system (after the turbo). The wastegate controls boost pressure by either a set-weight spring connected to a valve, and/or being controlled by a boost controller.
After the fresh air is compressed by the turbo(s), it travels through the cold piping to either an intercooler (which we’ll discuss later) or directly to the intake system. This is often clamped together with V-bands to reduce loss of boost pressure.
In the cold piping is the blow-off valve. This is the piece that makes the cool psssshhhhh noise. It bleeds off excessive boost under decel and when the throttle is closed. Otherwise, the pressure in the cold piping would cause the turbine wheel to pulse, which can damage the shaft bearings.
Single-turbo - The most popular turbo kits are the single-turbo systems. Because of their simplicity (in relation to twins), they are most widely used in OEM and aftermarket applications. A misconception about single-turbo systems is that a larger turbo is always better. If a turbocharger is too large for an application, it will not “spool up” (achieve its most efficient operating speed) quickly enough for the engine to take advantage of its larger diameter wheel.