How does those little device that are sold for a few hundred ringgit work andhow you can make one yourself for less than 30 bucks!
Basically, those device is nothing more than a flow control valve which taps onto the brake vacuum hose. It is tapped there because of its hose size. It is the biggest of all vacuum hoses. What this device does is it allows more air to enter the engine since the engine now has an additional source to suck air. Something like as if you have a larger throttle body. Also on cars with airflow sensor will run slightly leaner since air that enters thru this device does not get metered by the sensor. A normally aspirated engine will normally yield best torque in the 13.2:1 ~ 13.8:1 air fuel region. Many cars from factory run way to rich so leaning out the mixture can yield more power and better fuel economy.
So the question now is how do I make one? Go to your local hardware shop and get a ball valve and a brass T. Locate the brake vacuum hose. Cut this and insert the T the unconnected end of the T then goes to the ball valve. Open the ball valve half way and go for a spin. You have now got your self an E68/micrcompressor device. Experiment different open angles for best power... Once you're done. Get a engine cover breather and fit it on the open end of the valve so that dust doesnt get sucked in during idle and/or high vacuum situation. Here is a picture of a typical ball valve.