Electronic+Boost+Controller+Supplement

toc Written by Aikmeng Kuah, SPL PARTS INC. Jan 26 2003 Copyright SPL PARTS INC.

=How does a electronic boost controller work?= First, let us understand how a turbo works. A turbo simply consists of an exhaust wheel and a compressor wheel connected together, exhaust gases from the combustion turns the exhaust wheel which in turn spins the compressor wheel. The compressor wheel then crams more air into the intake, creating boost pressure.

If left alone, a turbo would just keep spinning faster and faster and could result in too much boost, which would cause engine components to fail. To regulate the amount of boost, wastegates are equipped on all turbo-charged cars. The purpose of the wastegate is to divert some of the exhaust away from the turbo (so it won't spin the exhaust wheel). A wastegate is simply a spring loaded valve, this valve opens when the intake pressure reaches a certain pressure and diverts some of the exhaust away from the turbo. Suppose the wastegate is designed to open at 7PSI of boost, then when boost reaches 7.1PSI, the valve opens and the exhaust from the cylinders are diverted away from the turbos, and the turbo starts to slow down. When the boost drops to 6.9PSI, the wastegate closes and the turbo starts to speed up again. This happens rapidly and keeps boost regulated nicely at 7PSI.

The pressure at which the wastegate opens is the base boost pressure, installing a boost controllers will allow you to run higher boost. An electronic boost controller usually works using a solenoid (electronically controlled) valve. A solenoid valve would have 3 ports (sometimes 1 is hidden inside the housing), and 1 port goes to the wastegate, the other port is hooked up to the intake, and the last port is left open to the atmosphere. The solenoid can switch between connecting the wastegate port to the intake port, or connecting the wastegate port to the atmosphere port.

Suppose you want to run 14PSI of boost, then a electronic boost controller should do this -- when the boost reaches 14.1PSI, the solenoid will connect the wastegate to the intake, causing the wastegate to open (since 14PSI is higher than the 7PSI required to open the wastegate)... the turbo will start slowing down, when it drops to 13.9PSI, the boost controller will then switch the solenoid and connect the wastegate to the atmosphere. This causes the wastegate to close since the atmosphere is 0PSI lower than the 7PSI needed to open the wastegate, and the turbo will start speeding up again. This happens rapidly and keeps boost regulated nicely at 14PSI.

Most boost controllers accomplish this by figuring out what percentage (or ratio) of the time the solenoid would connect the wastegate to the atmosphere vs. connecting the wastegate to the intake. This ratio is often known as the DUTY CYCLE, the duty cycle is directly related to the boost level.

Now this is the main function of the boost controller, but there is another benefit to running a electronic boost controller, and that is it will allow the turbos to spool up a little faster. How does it do this? Well, a wastegate might be designed to open at 7PSI, but it usually cracks open a little even before the pressure hits 7PSI. This will slow down spoolup of the turbo, causing it to hit 7PSI a little later. A good electronic boost controller would keep the wastegate shut for as long as possible, by using the solenoid to connect the wastegate to the atmosphere (0PSI) till the turbo gets really close to hitting the boost you want, only then it will start switching the solenoid back and forth according to the duty cycle. To determine how long to keep the wastegate shut, most electronic boost controllers use a number known as GAIN. If the gain is set too high, the boost could spike (the wastegate is held closed a little too long causing overboost), but if the gain is set too low, the spoolup is not as optimal as it could be. Getting the correct gain setting will give the optimal spoolup of your turbos.

=Manual mode vs. automatic mode vs. fuzzy logic= Most of the modern higher-end electronic boost controllers have an automatic mode or fuzzy logic, where you simply enter the boost you want to reach, and the boost controller would automatically try to figure out the DUTY CYCLE and/or GAIN. In certain cases (eg. twin-turbo setups), this logic might not work very well, and it would be necessary to use the manual mode.

=How to set up an electronic boost controller in manual mode= In manual mode, there are two numbers that has to be determined: DUTY CYCLE (sometimes also labelled as SET) and GAIN. The optimal gain number always depends on the boost level you want to run, if you are running very high boost, then you want the wastegate held closed for a longer time since it takes a longer time to reach the higher boost.

So the first step is to determine the duty cycle:


 * 1) Start off with a low DUTY CYCLE and GAIN setting.
 * 2) In a higher gear (3rd or 4th), run the car to see what boost level the duty cycle corresponds to by watching what steady/stable boost level is reached. Increment the DUTY CYCLE with each run till you reach the boost level you want. Fine tune as necessary. If you notice boost spikes, then you have set the gain too high, you do not want spikes at this point since that makes it more difficult to see the steady/stable boost level.The reason why you should use the higher gears is because in the low gears, things can happen too fast to figure out what the steady/stable boost level is. Now that you have figured out the duty cycle that will give you the boost level you want, the next thing to do is to work out the gain:
 * 3) Make runs in lower gear (1st or 2nd), increment gain with each run till you see boost spikes. Then fine tune it till there is little or no boost spike. This is your optimum gain setting for that boost level. The reason why you should use the lower gear now is because boost builds much quicker in the lower gears, so there is a higher tendency to boost spike.

When setting your boost controller, always have a passenger set the controller and watch the boost gauge for you, the driver should keep his eyes on the road!

=Common problem= Sometimes if the gain is set too high, it may appear to have the same effect as the duty cycle. If you notice (especially in the higher gears) that you initially hit the boost level you want, but then it starts tapering off, then you might have set the gain too high and the duty cycle is not set correctly. Or you might have a boost leak...