By Dave Koehler
What is it? A nitrous controller is often called a progressive box. A progressive box is an electronic gadget with a miniature computer. It allows you to limit the flow rate of nitrous and fuel available to the nitrous system and consequently the useable horsepower available to the tires.
The word progressive is supposed to mean that if you had jets in your nitrous system that could potentially produce 300 HP, you could set the controller to pulse for a period of time, limiting the HP and then ramping back up to full flow HP in the time span you dictate. This description is not entirely accurate, however. It’s kind of misleading to think that your HP is cut in half, for instance. Nothing has really changed as far as the potential HP level is concerned, which is dictated by your jets and pressures. What is really happening is that the solenoid is opening and closing enough times per second to limit the amount of time that the maximum flow rate is available to the jets. We call this opening and closing “pulsing.” Think of it this way. If you are in front of a spinning revolving door is it open or closed to you? Obviously only part of you can get through
unless you are super human quick, so it is closed for a moment. Open it a little slower and you can sneak by if you are quick enough. The same principle is how nitrous controllers operate. A nitrous controller slows down the maximum flow rate by turning the flow on and off in short bursts over a period of time.
WHY AND WHEN YOU NEED TO USE A PROGRESSIVE CONTROLLER
A nitrous controller is desired to soften the incredible torque spike that occurs with each stage of nitrous activation. You may have an engine with more torque than the car or track can handle or you have a tire limited class car (or both) with no wheelie bars and it
has a tendency to spin the tires. If you use a controller and reduce the amount of nitrous available to the engine just long enough to get the car moving forward then ramp in the full charge you will improve your ET, guaranteed.
Some folks try to do the power reduction with ignition retards (reducing total timing) combined with delaying the nitrous activation but this can bite you by producing bumper dragging wheel stands. While this works in some cases it is hard to take enough timing out and not have the pinion try to climb the ring gear and wheel stand the car. When you pull the timing back too far from the engine's ideal point and the nitrous is not activated, the engine really runs sour. While this wheelstand may get your car featured in DRO, you won’t win the race.
If you use the nitrous controller instead of ignition to accomplish this you can leave the timing where it needs to be with the nitrous on and avoid extreme wheel stands and losing. Usually it only requires 2-5 tenths of nitrous progressive duration to make the chassis work as it was intended and stick the car to the track.