One knob, many maps
Plenty of our customers want more than one personality from the same car. A mild setting for a wet track day, full boost when conditions are good, something sensible for the commute. You could reflash between tunes, but that means a laptop in the passenger seat. The cleaner answer is a 12-position rotary trim module mounted on the dash.
The module is simple. It has three wires: power, ground and a signal. Each click of the knob puts a different voltage on the signal wire, the ECU reads that voltage as a position number, and you use that position as an axis in whatever tables you want to change.
Setting up the module in ESP
- In ESP, open Setup, then Main Setup, then Functions, and choose Rotary Trim Module 1. Elite ECUs support up to three modules at once, and each one can drive as many functions as you like.
- Click Edit Connection and assign the spare input you've wired the signal to.
- Check the calibration tab. It already matches the voltage steps of Haltech's 12-position modules, so there's usually nothing to change.
- Turn the knob with the laptop connected and make sure the position channel follows it, one step per click.
Our rotary trim modules article covers the function settings in more detail.
Adding the knob to a map
Here's the process using boost as the example. It's the same for any table.
- Open the boost target table under Boost Control.
- Go to Setup, then Table Setup (F3 is the shortcut) to reach the axis setup.
- The table probably uses RPM on one axis already. Set the other axis to Rotary Trim Position Knob 1 and add the positions you plan to use.
- Click OK. The table now has a row for each knob position, and you fill in a different boost target for each.
Five positions is a good number for boost: something like low, street, sport, track and everything the setup can safely give. You don't have to use all 12.
Ideas beyond boost
| Table | What the knob can do |
|---|---|
| Boost target | Step boost up or down for traction, fuel quality or the occasion |
| RPM limiter | Pull the rev limit down low for a valet or loaner mode |
| Ignition | Carry a safer timing map for poor fuel |
| Target lambda / AFR | Run a leaner economy target for highway trips |
A favorite is a proper valet position: one click that drops boost to a low target and brings the rev limit down to a lazy 4500 RPM. Hand over the keys with a little more peace of mind.
If you want the knob to richen or lean the engine, put the knob axis on the target AFR (or lambda) table. With closed loop fueling active, the ECU learns toward whatever the target says. Put the knob on the main VE table instead and the closed loop learning simply trims your change back out to meet the unchanged target. See long term fuel trim for how that learning works.
Tips from the shop
- Label the positions on the dash. It sounds obvious until you're squinting at a knob at night.
- Make position 1 your safest map. If the signal wire ever fails, you want to know what the ECU will fall back to, so check it on the bench by unplugging the module.
- Change one table per position at a time when testing, and log the knob position channel so every run is traceable.
FAQ
Can one knob control several things at once?
Yes. Add the same knob axis to as many tables as you like. Position 2 could lower boost, the rev limit and timing all together.
Does this work on a Nexus ECU?
The same idea applies on Nexus ECUs in NSP. See our Nexus rotary trim module article. If you'd like us to build a multi-map setup for your car, get in touch.
