As far as we’re aware, the Independent Electronic Boost Control (IEBC) is
unique in the approach that it takes to controlling boost. So what is makes it
- The boost curve can be mapped at up to 64 points through the engine load
- Two completely separate boost curves can be mapped with on-dash switch
selection of each
- The placement of the boost control solenoid gives very quick and stable
Add to this the fact that the Independent Electronic Boost Control in kit
form costs very little (AUD$80 + hand controller at AUD$60) and you have a
killer boost control system!
But despite its low cost, this is not a system for a beginner. It won’t
- You put the electronic kit together wrongly
- You don’t test the system to make sure it is behaving as it should
- You plumb the solenoid in wrongly
- You don’t map the action of the solenoid correctly
If you expect to build the kit, fit it to a car, tune the boost curves and
being happily blasting around the road – and do it all in a few hours – you’ll
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 – 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
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 – 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
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 – 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
What You Need
To make this boost control system happen you’ll need three things: the IEBC
kit, the Digital Hand Controller Kit, and an electronic boost control solenoid.
(If your car already has an electronic boost control solenoid, use that.
Otherwise, source one from a wrecker.) The kits need fairly good soldering and
component recognition skills to assemble them, so if you’re a beginner in this
area, we strongly suggest you buy the built-and-tested versions. However, as
you’d expect, the built versions are more expensive than the kits.
(Note that even if you’re also using the Digital Fuel Adjuster and/or Digital
Pulse Adjuster kits, you need only one Digital Hand Controller. Since the Hand
Controller is used only during boost mapping, you can also share one Hand
Controller amongst a few friends.)
We strongly suggest that you also buy the book: High Performance
Electronics for Cars. Not only will this give you instructions in colour
(important for some of the wiring diagrams), but it also has chapters on how
electronic car systems work, how to build kits, and so on.
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 ‘duty cycle’ – 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
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 Controller
It’s very important that you test the operation of the controller before
trying to adjust boost with it. In addition to checking that all is working as
it should be, the tests will also make you familiar with how the system works.
To make it easy to see what’s happening, the controller has three status LEDs on
the board: one for power, one showing input signal and the other output signal.
When power and earth are connected correctly, the ‘power’ LED on the board
should light up. Additionally, the plugged-in hand controller LCD should light
and text should appear on the screen (at this stage don’t worry about what the
text says). (If the controller lights up but there’s no text displayed, make
sure that the contrast adjustment is turned up to full.)
As shown in the instructions that come with the kit, the first step is to
connect the input to an injector. This provides the duty cycle signal from the
injectors, so the controller always knows the engine load.
When the injector is connected, an INPUT load number will appear on the hand
controller, which will change as the engine is revved.
But what if this doesn’t happen? There are two reasons why it might not.
Firstly, you may have connected to the wrong side of the injector. And secondly,
the pot on the board needs to be adjusted until you get a clean input
signal. When the input signal is working correctly, the ‘input’ LED will
also get brighter with greater input duty cycles. IOTW, as engine power output
increases, the LED gets brighter.
If you cannot get a consistent input signal, even with the pot adjusted, you
may have a car that has ‘peak/hold’ injectors. In that case, you’ll need to buy
and build the Peak/Hold Injector Adaptor kit. Refer to High Performance
Electronic for Cars for more details.
The output can be tested in two ways. Firstly, with the engine idling (and so
an INPUT of say 3 showing on the hand controller screen when in RUN mode), press
the black UP button. This rapidly increases the output duty cycle for that load
site. As the output number increases, so the ‘output’ LED should get brighter.
(Note: it will also be flashing 10 times a second.)
Sometimes, the controller will jump back and forth between two input load
sites (eg 3 and 4). If this is the case, make sure you increase the output
number on both load sites so that the output is consistent.
Without power, input and output all working correctly, the boost control will
Constructors who have found that their IEBCs don’t work have most often made
mistakes with the on-board links. When positioning the links, make sure that you
follow the overlay diagram in the instructions, NOT the overlay screenprinted on
the board or the photo in the instructions. (The board screenprinting and the
photo are for the Digital Pulse Adjuster, which uses the same board but
different software in the PICs.) Also note the two PICs each contain unique
software – they can be differentiated by the placement of a stripe or a dot on
them; the instructions (see the first few pages) show which goes where.
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 ‘output’ 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.
Next week we’ll install the boost control solenoid and do the on-road tuning.
But before you get to that stage, always make certain the system is working
properly by doing the tests shown above.
Independent Electronic Boost Control – built and tested
Independent Electronic Boost Control – kit
Digital Hand Controller – built and tested
Digital Hand Controller – kit
Peak/Hold Injector Adaptor – kit
The Background Story
So how did this kit come about?
The Independent Electronic Boost Control was developed and designed by
electronics magazine. The kit, along with many others, is covered in the Silicon
Chip publication, High Performance Electronics for Cars. The book is a
must-have for DIY modifiers. The kit for the Independent Electronic Boost
Control is available from Jaycar Electronics
or through the
The electronics design and development of the Independent Electronic Boost
Control was carried out by electronics engineer John Clarke, while I came up
with the concept and did all the on-car development. (During this period I wore
a different hat to an AutoSpeed contributor, working for Silicon Chip
Publications as a freelance contributor to High Performance Electronics for
So by no means should the Independent Electronic Boost Control be seen as an
AutoSpeed-developed project, at the same time I am happy that AutoSpeed endorses
it and promotes it.