In the seven years of AutoSpeed we’ve covered all types of boost controllers. Everything from cheapy buy-it-online controllers to electronic controllers costing AUD$750. So what’s the deal? What boost control system is best for you?
In this article we’ll take a look at the characteristics of each boost control system we’ve covered.
DIY Boost Controller #1
One of the most tried-and-proven systems is the in-cabin boost controller discussed at Project EXA - Part 3 - DIY Boost Control. This system is suited to all turbo cars and is easy to install and calibrate.
The system uses two brass valves – a quarter inch needle valve (which becomes the in-cabin controller) and a quarter inch ball valve (which should be mounted under the bonnet and gives coarse boost control for set-up purposes). You’ll also need a quarter inch T-piece and a couple of metres of quarter inch hose. Total cost should be less than around AUD$75. Installation and calibration is discussed in our original article (Project EXA - Part 3 - DIY Boost Control)
So what are the characteristics of this system?
Well, the rate of boost rise is very fast but it's possible to achieve an even faster rise with other systems. Boost pressure stability also varies depending on the combination of turbocharger and engine. In some instances your newly set boost value will be held all the way to the redline – however, in some cars (particularly those with a relatively small turbocharger), it will fall off at high rpm. Note that this system is also susceptible to variations in ambient temperature and across different gears.
So, in summary, this system is reliable, easy to configure and cheap – but it doesn’t necessarily give the fastest rate of boost rise (if that’s what you want), it may allow boost to fall off near redline and it can’t compensate for changes in ambient temperature and across different gears. It may seem flawed but this system can work well – especially if you have an in-cabin boost gauge to keep an eye on.
DIY Boost Controller #2
This is the first Do-It-Yourself boost controller we’ve seen that incorporates adjustable wastegate creep – you can have a relatively progressive rate of boost rise or you can have it shoot up as quickly as possible. And, in contrast to the previous system, boost pressure is controlled using a pressure regulator rather than a bleed.
The Audi DIY Boost Control comprises two main components – a pressure relief valve (which allows adjustment of wastegate creep) and a pressure regulator (which allows adjustment of boost pressure). The pressure relief valve is fitted in the wastegate hose and the regulator is connected downstream (towards the wastegate actuator). The pressure relief valve can be set to open at, say 10 psi, so absolutely no pressure will reach the regulator or the wastegate actuator at boost pressures lower than this. This means boost can build as quickly as possible. Then, once the relief valve opens, the pressure regulator steps into action to control the amount of pressure applied to the wastegate actuator - and therefore control boost pressure.
In addition to these two main components you may also need a large diameter one-way valve which serves to improve boost response after gear-changes (by ensuring there is no residual pressure trapped against the wastegate actuator). The one-way valve is plumbed so that it connects the outlet end of the pressure regulator to the inlet end of the pressure relief valve. The valve is orientated so air can flow from the wastegate line to the input end of the pressure relief valve.
The biggest advantage of this system is the adjustment it gives over the rate of boost increase – you can have it exactly how you want. In terms of boost pressure consistency, the pressure regulator ensures the wastegate opens the same amount regardless of any other conditions. This might seem ideal, but in very cold conditions (where the engine can produce more power and, therefore, more exhaust gas than usual) we’ve seen this system allow over-boosting. Again, this is a good system to use in conjunction with an permanent in-cabin boost gauge.
At around AUD$100, the Audi Boost Control has been widely put into service with success. Its adjustability is the major drawcard, but be aware that – like a bleed - the pressure regulator does not ensure consistent boost pressure. Compared to the previous controller, it’s also slightly more difficult to install and tune.
DIY Boost Controller #3
The final Do-It-Yourself system we’ve devised is exclusively for use in cars with open loop factory electronic boost control - see Brilliant Boost and Bumped Up Boost. This is probably the trickiest Do-It-Yourself approach because, unlike the previous systems, the logic of the factory boost control system is retained. You’ll enjoy a ‘bumped up’ version of the factory boost curve along with all of the manufacturer’s safety strategies.
Extremely easy to set-up, this system involves installing a quarter inch flow control valve in the factory hose between the compressor outlet and the OE boost control solenoid. Start with the flow control valve fully open and adjust it so that the desired boost pressure is reached. It couldn’t be easier.
So what boost characteristics can you expect from this system?
Well, you’ll be able to set your maximum boost pressure but you can’t alter the factory boost curve – if the factory system brings boost up gradually and drops off toward the redline, then that’s what you’ll get. However, as a result of inserting the flow control valve in the wastegate hose, you can expect boost to rise slightly faster than standard. In addition, you’ll have the protection of OE failsafe strategies which, for example, might involve a reduction of boost pressure when the airflow meter signal is detected faulty.
For under AUD$50, this is an easy to install, safe and well integrated approach to boost control and should appeal to anyone not wanting to ‘throw the baby out with the bath water’.
Stick around for the second and final part of the series – we look at off-the-shelf aftermarket boost controllers...