my theory
until someone can provide proof of operation that proves different then this is my theory of how it works.
http://img112.imageshack.us/img112/8853/sprintue4.jpg
load of b****cks !!! as wot is the same with or without the sprint booster thingy
All that would require is a revised throttle potentiometer, or a change to the linkage.
Since it involves a computer I would suggest it might work quite differently and much smarter to that. And if it doesn't it should. I would suggest that it works like brake assist.
The way the cable throttle on mk 1s work is the throttle butterfly moves AS you push the throttle pedal. And the way the mk 2s electronic throttle works is that every tenth or whatever of a second the ECU reads the throttle pedal position potentiometer THEN sends a signal to the stepper motor in the throttle body telling it to move to there. So there's a delay. With the electronic throttle the butterfly only goes to that position some time (albeit a small time) AFTER your foot moves the throttle pedal to that position.
But the way brake assist works on cars that have got it is that the computer measures how hard you're pressing the brake pedal by measuring how fast it is being pushed down, and when it detects that you've hit the pedal hard in what is apparently a panic stop it doesn't wait for you foot to get all the way to the floor it anticipates it and gives you maximum braking immediately. I would think that is what this device does for the throttle. It measures throttle pedal pressure by the rate its heading for the floor. It anticipates you wanting full throttle and passes the ECU a signal to say your foot is all the way to the floor, and to open up the throttle body all the way BEFORE your foot has actually gotten all the way to the floor. OK, it not a lot of time earlier, but when you're only talking seconds, getting full throttle a couple of tenths of a second earlier is the equivalent of a significant increase in horsepower.
I can't draw a graph of that because it'd have to be a three dimensional graph. The cable throttle gives you the throttle butterfly position you want AS you ask for it. The standard electronic throttle gives it to you a small but noticeable time AFTER you ask for it. And this box tries to anticipate what throttle position you want BEFORE your foot has got all the way there based on two things, where your foot is AND how hard (ie, fast) its pressing the pedal.