What a dual intake runner does
Runner length tunes the intake's pressure waves to a certain RPM range. Long runners help torque down low. Short runners, or an opened secondary path, let the engine breathe at high RPM. A variable intake uses a valve, usually driven by a vacuum or electric solenoid, to move between the two. The Dual Intake Runner (DIR) function in ESP drives that solenoid based on engine speed, with the switch point allowed to change with load.
Most systems turn on at one RPM and stay on as RPM keeps climbing. Some also switch back off above a second, higher RPM. Because the function is really just an RPM and load controlled on/off output, you can use it for other jobs that need that behavior too, such as an auxiliary valve or device that only needs to run within an RPM band.
Wiring tab
- DIR Output: the ECU output wired to the runner control solenoid, usually a DPO (digital pulsed output).
- Active State: sets the output's polarity. At the default of Low, the ECU grounds the wire when DIR is on. High flips that, so the wire is grounded when DIR is off and released when it's on.
Most solenoids are fed switched 12V on one side and grounded by the ECU on the other, so Low is the usual choice. Use High only if your valve's default position is the opposite of what you need, and double check it with the output test before driving.
Switching Points tab
RPM Hysteresis
Hysteresis is a small buffer applied as RPM falls back through a switch point. Without it, an engine sitting right on the switch RPM would flick the valve on and off constantly. With it, the output has to drop a set amount below the threshold before it changes back.
On and off points that move with load
Instead of one fixed switch RPM, ESP lets you define the switch point at a low load and a high load and blends between them.
| Setting | What it does | Our advice |
|---|---|---|
| Min Load | The low-load reference. Anything below it uses the Min Load RPM values | Set around light cruise load |
| Max Load | The high-load reference. Anything above it uses the Max Load RPM values | Set near full load |
| Min Load On RPM | RPM where DIR turns on at or below Min Load | Find it on the dyno at part load |
| Max Load On RPM | RPM where DIR turns on at or above Max Load | Where the two torque curves cross at wide open throttle |
| Off RPM Condition | Enables a second, higher point where DIR turns back off | Leave disabled (the default) unless the manifold needs it |
| Min Load Off RPM | RPM where DIR turns off at or below Min Load (Off condition only) | Only if your system switches back |
| Max Load Off RPM | RPM where DIR turns off at or above Max Load (Off condition only) | Only if your system switches back |
Between Min Load and Max Load, the ECU interpolates, so the switch RPM slides smoothly from one value to the other as load changes. With the Off RPM Condition disabled, the output simply comes on above the On RPM and stays on until RPM drops back below it (less the hysteresis).
Worked example
Say dyno runs show the long runner position makes more torque below 4,400 rpm at full throttle, and the short position wins above that. At light load, the crossover happens lower, around 3,800 rpm. You might set:
- Min Load at your light cruise load, with Min Load On RPM at 3,800.
- Max Load near full load, with Max Load On RPM at 4,400.
- A modest RPM hysteresis so the valve doesn't chatter when you hold RPM near the switch.
- Off RPM Condition disabled.
At half-way load, the ECU would switch around 4,100 rpm, halfway between the two. These numbers are only for illustration. Every manifold is different, and the right points come from back-to-back pulls with the valve locked in each position.
How we find the switch point
- Make a full throttle pull with the valve held closed (DIR disabled or On RPM set above redline).
- Make another with it held open (On RPM set very low).
- Overlay the torque curves. Where they cross is your Max Load On RPM.
- Repeat at a lighter load if the car will spend time there, and use that crossover for Min Load On RPM.
- Re-tune fuel and timing around the switch. Volumetric efficiency changes when the runners change, so expect the fuel table to need attention there.
Troubleshooting
| Symptom | Usually |
|---|---|
| Valve never moves | Wrong output assigned, no 12V to the solenoid, or a vacuum supply problem on vacuum-operated valves |
| Valve works backwards | Active State set the wrong way for your solenoid |
| Valve chatters near the switch point | Hysteresis too small |
| Flat spot or lean spike at the switch | Fuel table not tuned for the change in airflow at that RPM |
FAQ
Can I use DIR for something other than an intake manifold?
Yes. Any device that just needs to turn on above a certain RPM, optionally varying with load and optionally turning off again higher up, can use it.
Is this the same as the Nexus function?
The idea is the same, but the settings differ. For Nexus ECUs in NSP, see Dual Intake Runner for Nexus and DIR wiring.
Related Elite functions worth a look: switched cam control and air pump control.
