Last week we introduced the Independent Electronic Boost Control (IEBC), an
electronic kit that allows full control over turbo boost. The IEBC is tuned
using a Digital Hand Controller and once this has been done, two different boost control curves can
be selected by a dashboard switch. (Go to The Independent Electronic Boost Control, Part 1).
The IEBC works by monitoring injector duty cycle so that it always knows the
exact engine load. The flow of the boost control valve is then set for each
engine load point, resulting in boost being mapped against engine load. This
approach gives much better throttle control than a conventional "get to 20 psi
and hold it there" system while still always giving max boost when you do actually nail it.
In Part 1 we tested the IEBC, making sure it recognised the input
injector signal and could drive the output boost control solenoid over a variety
of flows. Now it’s time to install the boost control solenoid. (Note that the
installation of the system is covered in much more detail in the book, High
Performance Electronics for Cars which we recommend you buy.)
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
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.
After the RESET Button the Hand Controller has been pushed for 5 seconds, the
output to the solenoid valve at all engine loads is returned to zero.
This means the initial tuning configuration results in NO control over
To tune the boost curve, you’ll need an assistant and a boost gauge. The
first step is to pick which boost curve you want to tune first – H (High) or L
(low). This is selected by the switch on the main controller (the switch can be
mounted anywhere you want).
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 ‘NOW!’ 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
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
The rule to remember is: the higher the output number, the lower the boost
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 – 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.
A Sample Tuning Map
Here is an example of a boost tuning map from a Nissan Maxima V6 Turbo.
As can be seen, for about the first half of the engine’s power range, the
wastegate is kept completely shut (ie from Load Site 0-28). This gives the
fastest possible boosting.
Then, as the turbo starts to come on boost hard, the solenoid is ramped open,
rising to a maximum duty cycle of 44 per cent. This transitions the
fastly-rising boost to the level that is to be held across the rest of the rev
The solenoid is kept at this value until....
...the top end of the engine’s power output, where – because boost would
otherwise have started to drop off - the solenoid output is progressively
decreased, so closing the solenoid. At full engine power (load site 64), the
wastegate is again nearly shut.
This tuning map resulted in a ruler-flat boost curve – the high-speed
data-loggged boost curves in each gear are shown in High Performance
Electronics for Cars, but as a guide, once it reaches maximum, boost varies
by only 0.25 psi all the way to the redline.
Assuming the turbo and wastegate can flow the gases, with the IEBC it’s
possible to have:
- Boost reach its peak level and stay at that level
- Boost increase progressively until the redline
- Boost reach its peak and then progressively decease
- Boost reach its peak and then hold steady until the last 1000 rpm, where it
- Boost come on gently with lots of wastegate creep
- Boost come on as hard as physically possible by keeping the wastegate closed
....or whatever other boost behaviour you want!
The result is a tuning flexibility that we think is impossible to achieve
with any other boost control system.
It all starts getting a bit complicated, but if you look at this diagram
you’ll see that while - strictly speaking - the IEBC is not a closed loop boost
controller, it does have some closed loop aspects.
The injector duty cycle depends on a bunch of factors that contribute to how
much power the engine’s making at that time – throttle position, RPM, intake air
temp, ignition timing and boost pressure. (Yes, all of these factors are
automatically taken into account by measuring just injector duty cycle. Injector
duty cycle is a very ‘information rich’ signal.)
If changing the turbo boost level changes injector duty cycle (which it will
unless the injectors or airflow meter/MAP sensor are maxxed out, or you’re got
enormous exhaust backpressure where increasing boost doesn’t increase power)
then the IEBC will respond to this change.
The IEBC isn’t a beginner’s system but it’s one that can be set up to give
fantastic results at a cost lower than anything that even comes close.
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