Revealing secrets about digital nitrous controllers and how they work
Words: Jeff Smith and Greg Connoyer; Photos: Jeff Smith
It’s almost cliché that big horsepower numbers are incredibly easy to make these days. Big horsepower is not hard to make — or even all that expensive. The challenge becomes how to harness all that power in such a way that you are quicker than the next guy. Otherwise, horsepower is just bragging rights.
Nitrous has been a popular power-adder for more than 30 years and is acknowledged as one of the easiest, quickest, and least expensive ways to make impressive horsepower. The tribal knowledge that’s been passed down by expert tuners now can make even serious 350- to 500-hp packages live over hundreds of runs. One of the best ways to manage all this nitrous power is with a progressive digital nitrous controller.
There are probably two dozen different progressive controllers on the market today — so many that we’re not going to even attempt to mention them all. Companies like Edelbrock, Dedenbear, Induction Solutions, NOS, Nitrous Express, Wilson, and several others have multiple offerings that range in price and complexity. Then there are aftermarket EFI systems like Holley’s Dominator or HP programs that also offer EFI control over nitrous. We will focus this story on a couple of different controllers in an attempt to cover the variations on the theme.
But let’s start with some basics first. In its most simplistic form, a nitrous system hits the engine with the “all or nothing” approach. At the starting line, this is generally too much power. So the digital solution is to introduce a small percentage of the total power package. All nitrous controllers accomplish this by employing the simple principal of pulsing the nitrous and fuel solenoids.
In the early days of nitrous systems, tuners achieved control by using multiple stages of nitrous to progressively adding more power. Now, with digital control, tuners can simplify the mechanical side of nitrous by using a single, high-output stage of nitrous and electronically pulse both the nitrous and fuel solenoids to control the amount of nitrous delivered to the engine. This control is achieved by a combination of on/off time — exactly the same way electronic fuel injectors are managed. Engineers call this pulse width modulation (PWM) and express it as a percentage of “on” time from 0 to 100 percent.
Using a progressive nitrous controller, the tuner has very finite control over pulsing the nitrous and fuel solenoids to a specific percentage. For example, with a big, single stage of nitrous, the tuner can use a progressive controller to pulse both the nitrous and fuel solenoids to operate at varying percentages. A simple example would be by initiating the system with a small percentage, like 20, and progressively increasing this to 100 percent over a given amount of time, such as 6 seconds.
If this progressive control was displayed on a graph, which some controllers offer, the curve would be a sloping straight line, increasing the percentage of nitrous and fuel flow moving from left to right. Many of the more sophisticated controllers (and even some simpler ones like Edelbrock’s) allow the tuner to create non-linear curves with multiple steps or plateaus — often called dual ramp curves. It all comes down to what the car wants to get down the track as quickly as possible.
Many of the more advanced controllers offer multiple options beyond simple time-based control. For example, a few offer vehicle speed-based control where the nitrous is tied to a threshold velocity like 30 mph, but this usually requires a digital vehicle speed sensor (VSS) input.
Another option is throttle position-based control based off of input from a throttle position sensor (TPS). All of these can delay nitrous onset using time, speed, or throttle position inputs. For example, you could delay nitrous onset until the throttle is 100 percent open. Still another possibility, which includes the Lingenfelter system, offers the option of delaying onset of the nitrous solenoid, essentially giving the low pressure fuel solenoid a head start to avoid a potential slight lean condition in the manifold.
This would also be a good point to define a crucial concept with digital progressive nitrous controllers. The “solenoid opening” rate is also often expressed as a hertz (Hz), which is the number of opening and closing cycles per second. So a 20 Hz rate would open and close the solenoid 20 times per second. In addition, increasing the hertz also increases the number of data points per second where you can change the solenoid’s rate.
While tuning these systems is not difficult, Steve Johnson from Induction Solutions offered some intriguing information that might shed some light on what’s happening inside the intake manifold, to make the tuning a little easier. Many tuners naturally assume that a 50-percent pulse width command for a 300-hp nitrous system would represent a 150-hp increase in power. According to Johnson, a long time nitrous tuner, this is often not the case. There are multiple variables that come into play with regard to pulse-width com-manded percentages, including solenoid flow rates, jet flow rates, system voltage, the Hz of solenoid opening, and perhaps a dozen other factors. Perhaps the best way to illustrate the complexity is with an example.
Johnson passed along some numbers pulled from one of his customer’s data log. Induction Solutions has built its own custom nitrous flow bench where they can flow a functioning nitrous system and measure the flow rate of both the nitrous and the fuel. Then, using the nitrous flow rate, Johnson calculates a horsepower number that is associated with that combination of fuel and nitrous flow. The bench allows them to custom set the nitrous-to-fuel ratio to allow safe operation of the system.
In this situation, the customer’s single stage kit flowed the equivalent of 485 hp at 100 percent duty cycle. We won’t reproduce the entire curve, but instead use just three basic data points. The Percent Command column is the nitrous solenoid’s duty cycle. The Perceived HP column represents what you would expect the system to deliver based on the commanded percentage of the actual total horsepower the system produces. The Actual HP is the horsepower equivalent of nitrous flowed by the solenoid. The Percent of Total HP is the percentage of the 485 hp total to use as a comparison against the Percent Command. The final Accuracy column is the difference between the commanded percentage and the actual HP percentage.
|32%||155 hp||88 hp||18%||-14%|
|34%||165 hp||141 hp||29%||-5%|
|44%||213 hp||301 hp||62%||+18%|
There’s a wealth of information in these three data points. In the first line, notice that despite commanding 32 percent (155 hp), the actual power was barely 18 percent (88 hp) of full power. The second line increased the PWM command only 2 percent (to 34 percent), and yet the power almost doubled from 88 to 141 hp. This was the closest of the three tests with an error factor of only 5 percent. Line three commanded 44 percent, yet generated 62 percent of the total power.
If you stand back and look at both the commanded and actual power curves, they both are linear. The actual power is wildly different from what you would think the PWM control would deliver. We subtracted the actual percentage of power from the commanded percentage to create that far right column called Accuracy. As you can see, the first command under-delivered by 14 percent, while the second was the closest with a mere 5 percent under-shoot. The third percentage over-delivered power by 18 percent.
Johnson says the customer’s data logger reported that the car tended to haze the tires when 34 percent was commanded for only 0.20-second. Johnson said rather than reduce the percentage, they instead lengthened the 34 percent time to 0.06-second and solved the problem. Part of the issue of inaccuracy may be the steepness of the commanded ramp. But the more important point is that even with finite digital control, there are huge variables that affect accuracy.
It’s important to also note the actual delivered horsepower really isn’t all that important compared to the commanded percentage number, as long as you understand that increasing the percentage will increase the power and vice versa. The important issue to understand is that the actual power numbers will likely not be linear. In complex issues like this, everyone tends to think in terms of linear steps, while Johnson’s testing reveals it’s entirely possible systems may not always deliver as expected. The best way to understand how your system responds would be to have Induction Solutions flow test your system with the controller, in order to really understand what’s happening.
Crucial to understanding how your system will perform on the track would be accurate data recovered from each run, so you can use that information to make intelligent decisions for changing track conditions. This is where a dedicated data logging feature is incredibly useful. For example, both the Induction Solutions and Lingenfelter controllers offer an internal data logger that captures basic information that can be used to evaluate the run.
Information that can be logged includes engine rpm, nitrous on/off, vehicle or driveshaft speed, air-fuel ratio, battery voltage, nitrous system pressure, fuel pressure, and more depending upon the system. Of course, if you already have a data logger program, then a controller with data logging capability isn’t all that important.
We’ve barely scratched the surface of how nitrous controllers work, how they operate, and the limitations of the system. But, even with their foibles, nitrous controllers are an outstanding way to manage a thumpin’ nitrous system that can help you lay down a killer pass.
Sources: Daytona Sensors, Daytona-Sensors.com; Edelbrock, edelbrock.com; Holley Performance Products (NOS), holley.com; Induction Solutions, inductionsolutions.com; Lingenfelter Performance Engineering, lingenfelter.com; Nitrous Express, nitrousexpress.com; Nitrous Pro-Flow, wilsonmanifolds.com