Much of my automotive knowledge comes from reading magazines and PR material written by my peers. This was especially the case when it came to knowing aftermarket products. As I didn't have a lot of hands-on experience, I frequently had no idea how a lot of products actually worked. The buyers guides I read only related what a product was for and all the fancy features it had; there was nothing on how anything actually worked. I needed that hands-on experience.
Take boost controllers and piggyback computers, for example. It wasn't until I went out and blindly purchased a$500 boost controller and installed it myself that I finally understood how they worked. What follows is what I learned, along with a list of the various units on the market.
Before I talk about boost controller units, however, you need to understand how turbocharging systems on a reciprocating internal combustion engine work. Without going into overwhelming details (such as drawing pressure-volume (P-V) diagrams) here are the basics and how they relate to boost control.
The engine in your car is basically an air pump that sucks in air and expels it back into the atmosphere at a higher pressure. At some point someone realized that the efficiency of this air pump can be increased by scavenging the wasted thermal and kinetic energy of the exhaust gases and use said energies to compress the intake gases and thus increase the intake air mass. That's what a turbo does. More air pushed into the cylinders for combustion means more gas to expel, which increases the exhaust gas flow and energy available to build boost.
Without regulation, this cycle continues until either the turbo or the intake track reaches its flow limits. Before this occurs, though, the increased combustion pressures and stresses become too high for an engine to safely operate under. So there is a need to control the amount of boost generated by the exhaust-gas-driven turbocharger.
To do this, the speed of the compressor wheel in the turbo must be limited by governing the speed of the turbine wheel on the exhaust side as they share the same axle. A wastegate-internal or external-is used to regulate whether or not exhaust gases are bypassed around the turbine wheel. By bypassing the exhaust gases, the amount of energy available to spin the rotating assembly becomes limited and thus the amount of boost is limited. The wastegate operates as a pressure valve that is referenced to the exhaust-gas pressure and intake-manifold air pressure (MAP). Only when at target boost level does the valve open to let exhaust gases bypass the turbine.
So why do you need a boost controller if the wastegate already regulates boost? Because a boost controller doesn't directly control boost, it controls the MAP that the wastegate is referenced to and thus alters when and how the wastegate opens. Without boost, the MAP will always be a vacuum, sucking the diaphragm and exhaust bypass valve shut, ensuring that all the exhaust energy goes into spinning the turbine.
As boost builds, the MAP will start slowly pushing the wastegate diaphragm up against the spring that is loaded to the same pressure as the target boost. Ideally, when MAP reaches the target boost, the pressure overcomes the spring holding the valve closed and then pops the assembly open. In the real world however, this is not the case. As boost climbs, the valve creeps open under the increased pressure applied to the diaphragm and bleeds exhaust gases around the turbine, thus making additional boost harder to generate. This really slows boost response.
So a boost controller (BC) is simply a valve put in line between the manifold and the wastegate reference that alters the response time of the wastegate opening and losing. The valve can be manually controlled or electro-mechanically actuated with either a solenoid or stepper motor. The actuator's role is to essentially pinch off the vacuum line that the wastegate is referenced to, preventing premature opening of the bypass valve. OEMs and the aftermarket both use similar technology, so a N75 valve found on turbocharged Audis and VWs is just a solenoid controlled by a Motronic ECU.
Since most modern turbocharged cars come with an integrated boost controller, the units shown in this guide are better suited for aftermarket bolt-on turbo kits or turbo upgrades where the turbo generates boost pressures beyond the controllable range of the factory controllers. These are generally referred to as "piggyback" electronic BCs and usually require a separate MAP sensor. The MAP sensor is used as the sensory element of a feedback loop to detect and control boost pressure so that the controller can accurately achieve the target boost. The speed at which the target boost is acquired is controlled by the gain of the feedback loop and is determined by BC tuning.
Although this guide does not cover all of the piggyback BCs on the market-and only offers a precursory glance of their capabilities-each type of controller from every category is represented here. These units can be used on external- and internal-wastegate applications, and most can be plumbed to operate twin-turbo setups. Other more advanced BCs, such as add-on modules to stand-alone engine management systems, have been left out of the guide. When choosing a BC, one helpful way to determine its level of sophistication and functionality is to look at its wiring diagram to see the types of signals it requires to operate. Don't forget that simplicity can be advantageous. I also included some of the turbo timers available from the same manufacturers.