Hi this is a cut & past summary from a guide to building an independent boost controller but I hope it helps, it was based around an Audi boost control solenoid
Jason
So how does it work? The IEBC measures engine load by monitoring injector duty cycle (ie how long the injectors are open for) 200 times a second. By using injector duty cycle as the input, it always knows exactly how much load the engine is under —a and it provides the boost that you've chosen to match that load. The control of boost is achieved by varying the wastegate solenoid duty cycle.
So in summary, all that's done is to set what wastegate duty cycle applies at each injector duty cycle.
Sound a strange way of doing things? Nope. It has huge advantages over a control system that measures boost pressure and then always tries to make it as close to maximum as possible. In fact, if you've driven a big turbo car with a traditional "keep the wastegate shut until 20 psi is reached" you'll know that such a system has terrible throttle control. At high revs you might get 20 psi boost at half throttle, three-quarters throttle and full throttle —a which makes much of the accelerator's range useless for finely controlling power! Cornering a car like this on the throttle needs huge skills, as waves of boost keep coming and going with slight ankle twitches.
But with the IEBC you always get boost that's proportional to throttle position (cos throttle position is proportional to load). So at 4000 rpm, half throttle, you get less boost than at 4000 rpm, full throttle. If you put your foot down, you still get max boost so there's absolutely no drop-off in available power, but at the same time you get far better throttle control. And making boost proportional to load also decreases the average temp of the air the intercooler sees.
But even if you're only interested in full-throttle performance, the IEBC has huge advantages over its nearest cost competitor, a pneumatic bleed. For starters, you can keep the wastegate shut as engine load increases, completely dialling-out wastegate creep. Then you get easily get rid of the drooping top-end boost curve that often occurs with bleed systems. And finally, there's in the in-cabin switch that lets you select two completely different boost curves —a nope, not just peak boost levels, but the shape of the entire boost curve. That means you can have a wet weather map that brings on boost more gently and peaks at a lower level, for example. The dry road map? Well, that can have a heap of wastegate anti-creep built in and hold boost at a higher level.
How the Solenoid is Pulsed
Unless it's set so that it's ether fully open or fully shut, the boost control solenoid is pulsed 10 times per second. When only a small amount of air is required to pass through it, the time that the solenoid is open for is very short. When lots of air needs to pass through it, the solenoid is open for much longer. This opening time is called â€Ëaduty cycle' —a the expression has the same application as with injectors.
As can be seen in this scope view of a working IEBC, at 5 per cent duty cycle the solenoid isn't open much at all. (Look how narrow the peaks are.)
However, at 70 per cent duty cycle, the solenoid is open for over two-thirds of the time.
Most boost control solenoids will work over the range of 5-80 per cent, giving 75 different levels of airflow through the valve. Since you can set the solenoid airflow at 1.5 per cent injector duty cycle intervals, there are thousands of different values that are available to control boost! But don't panic: if you want a smooth boost curve, road tuning soon shows the values to use - once the map has been started, the rest of the figures are easy to select. We'll cover more on boost tuning next week.
Testing the Solenoid
Now that the controller is working, you can connect the boost control solenoid. At this stage it doesn't need to be plumbed to the turbo. With the solenoid wired between 12V and the controller's output, try changing the output signal going to it by adjusting the hand controller's up/down buttons at that input load site. (You can easily do this test with the car just idling.)
In addition to the â€Ëaoutput' LED changing in brightness, you should be able to feel and hear the solenoid clicking. Change the output number across a wide range and check the duty cycle at which the solenoid stays fully open and then fully shut. (Solenoids won't work over the full 1-100 per cent range; typically they'll work only over say 5-80 percent.)
Blow through the solenoid and check that at zero output, the solenoid is shut and that at 100 per cent output, the solenoid is open. Then try some in-between duty cycles and check that the flow varies as it should.
Boost Control Solenoid
It's important to note the boost control solenoid is NOT installed as with a conventional system. Instead of the boost control solenoid being used to bleed off air that's going to the wastegate actuator (so reducing the pressure the wastegate actuator sees), the IEBC's solenoid is actually placed in-line between the boost pressure source and the wastegate.
IOTW, when the solenoid is shut, no boost pressure at all can get to the actuator.
The above diagram shows how the solenoid is plumbed-in. As can be seen, a small vent is also placed between the solenoid and the wastegate. This prevents pressure being trapped between the closed solenoid and the wastegate actuator when the solenoid is shut. The small vent is most easily made by soldering up one arm of a brass T-piece and then drilling a small hole (eg 1mm) through the solder plug. Alternatively, a quarter-inch needle valve can be used to give an easily adjustable opening. The T-piece is available at any auto parts store while the needle valve can be bought at hydraulics and pneumatics suppliers.
Boost control solenoids are usually directional. When installing the valve under the bonnet, be careful not to plumb the valve in wrongly or it may leak, making boost control impossible.
Tuning
To tune the boost curve, you'll need an assistant and a boost gauge. To start the on-road tuning process, put your foot down at low revs in a higher gear (like third) and watch the boost gauge like a hawk. Boost will shoot up rapidly and when it's just below the peak level you want, yell out â€ËaNOW!' and immediately back off the throttle. The assistant should watch the Hand Controller (set to RUN mode) and note the load site number that occurred when you yelled.
If for example, it was at Load Site 34 that you yelled, increase the output number at the ten sites in front of (and including) Load Site 34. This is easily done by going into VIEW mode and then scrolling across until you reach these load sites.
Drive the car at full throttle again and the boost level shouldn't reach your max until higher loads. Continue adjusting the outputs at the new load sites until you have the maximum boost set correctly. If you find that the boost level surges, it's probably because you have the duty cycle of the solenoid ramping up too quickly —a start bringing on its action at an earlier load site. In other words, never have too big a huge jump in output between adjoining load sites or the boost control may become erratic as the controller switches back and forth between these sites.
You can then concentrate on the rest of the boost curve, fine-tuning the way the turbo comes on boost and making sure that it remains constant throughout the rev range (or has the boost curve shape you want).
Once you realise you can increase or decrease boost anywhere you want through the load range, the power of the controller becomes obvious.
