anti knock unit
The unit system is used by auto maker on all of their turbo cars . The unit adjusts the charge air pressure automatically to the maximum possible for the grade of fuel used at any given time. Fuel available to the pumps has been quite irregular in quality for some time now. The unit system enables the engine to achieve ideal performance regardless of the grade of fuel in the tank.
Under heavy engine loads, knocking and pinging can occur. Knocking is caused by pre-ignition of the air fuel mixture. Pre-ignition causes high heat and stress loads on an engine which can cause serious damage if allowed to continue. There is another type of knocking that occurs at high engine speeds which is inaudible to the human ear. This inaudible knocking is the most damaging to the engine.
In most cases, manufacturers restrict the performance to allow for fuel quality variations. Unfortunately, not all of the full energy potential can be extracted from the fuel, and is lost in the form of heat. The unit system is a mostly transistorized system with only one moving part. This makes the system very reliable and unlikely to give any trouble.
"How much performance does the unit add?"
After initial installation, the performance gain was quite noticeable. I hooked up a graduated pressure gauge to get some exact numbers. The stock boost setting on the car is supposed to be 10 psi, but is often lower than that in real life, in my case it was about 8 psi
The needle on the stock gauge is currently reading right to the end of the gauge on the dash which I confirmed to be 14psi with an accurate graduated gauge. The turbo also spools up faster to the max pressure.
"how it works"
The unit listens for knocking and retards the boost in increments of 1.5 psi until the detonation goes away and attempts to bring it back as much as possible until detonation is detected then retards the boost again. This prevents the engine for being damaged by knocking and pinging while allowing the maximum boost possible. Neat trick huh?
The unit receives signals from several transmitters, and in turn processes those signals and uses the data to adjust the charge air pressure. It does this by actuating the wastegate with an electrically operated solenoid valve tapped into the pressure line to the wastegate. The following sensors are used by the control unit to determine charge air pressure: The main sensor is the knock sensor. The knock sensor is a piezo electric sensor that is used a lot like a microphone to listen for detonation. There is a pressure transducer to sense the pressure in the intake manifold upstream of the throttle plate. The unit also uses a signal from the ignition to determine engine RPM.
anti knock selonoid valve
The solenoid valve regulates the charge air pressure. It is connected in the line from the turbo to the waste gate. The inlet port of the solenoid valve contains a fixed diameter restriction. The waste gate actuator is connected down stream of this restriction. The diameter of the outlet port of the solenoid is governed by the frequency and duty cycle that the valve is oscillating at. When energized, the solenoid valve oscillates between the open and closed positions at a fixed frequency of 12hz (12 times per second). If the boost pressure rises above 6 psi (.4bar), the pulse width of the valve will change. The pulse width is the relationship between the amount of time that the solenoid is open and the amount of time that the solenoid is closed within that 1/12 of a second cycle.When the valve is fully open (energized), pressure is evacuated through the "R" port, to the inlet side of the compressor. The restriction in port "C" is so narrow in comparison with the valve opening that there is a total pressure drop in the small quantity of air flowing through the restriction, thus preventing the waste gate from actuatingWhen the solenoid valve is fully closed (de-energized), the waste gate actuator is connected to the full pressure present from the compressed charge air. Since the R port is closed off, the pressure to the waste gate is no longer allowed to dump to the inlet side of the turbo compressor. Therefore, the waste gate is allowed to open and the boost is reduced to the basic setting. The "Basic boost setting" is that which the waste gate would normally open at without any intervention from the anti knock unit.The routing of the solenoid hoses is quite simple. As you're looking at the solenoid with the ports facing you, The port on the left goes to the intake upstream of the turbo and downstream of the fuel metering device (air mass meter, or the air flow plate). there is a very expensive formed rubber hose that goes from the air mass meter to the intake of the turbo. There was no good way to tap into this hose, but I was able to build a T fitting in the line from the crank case ventilation to this hose. The center port with the restriction in it goes to the fitting on the side of the turbine housing of the turbo. On my turbo, there was a 90 degree elbow on it which I rotated to the necessary position for hookup to the solenoid. The port on the right goes to the waste gate actuator.This is a picture of the solenoid valve mounted on the inner fender in front of the coolant reservoir, and behind the air filter housing..
The whole idea of the anti knock system is to allow for maximum boost without detonation or knock. Knocking is an explosion of the air fuel mixture as opposed to a normal controlled burn. When running at high boost pressures, there is a tendency for violent knocking. In order to push the limit of maximum boost without damaging the engine, you must protect the engine from this danger. Knocking combustion causes greater thermal and mechanical stresses on the engine that could damage it due to pressure fluctuations and increased heat loads. The knocking noise heard is caused by gas vibrations.The knock sensor is an acceleration sensor that converts vibrations into electrical signals by way of a piezo-ceramic element. The piezo-ceramic element generates surface charges when mechanical forces act upon it. Knocking causes vibrations in the engine block that exhibit a characteristic frequency between 5 and 10 kilohertz . In order to filter out erroneous noises caused by other mechanical components in the engine the anti knock unit system's brain has the ability to read the signal from the knock sensor, decode it, and make a knock/no knock decision. If the anti knock unit hears knocking it then retards boost in increments of 1.5psi until knock goes away.
The pressure transducer senses the pressure downstream of the throttle butterfly. The pressure has a linear effect on a resistor inside the transducer which controls the signal to the control unit. The pressure transducer will maintain the maximum charging pressure at the correct value, despite the changes occurring due to normal wear and tear on the engine components during the life of the car. The vacuum line to the transducer tees into the vacuum line for the turbo gauge just before it goes into the firewall