AutoSpeed - The Independent Electronic Boost Control, Part 2

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 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

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 boost!

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 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.

The rule to remember is: the higher the output number, the lower the boost level.

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 range.

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 gradually decreases
Boost come on gently with lots of wastegate creep
Boost come on as hard as physically possible by keeping the wastegate closed longer

....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.

Closed Loop?

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.