Testing And Logging NOS With Holley's Terminator X EFI System On A Foxbody Mustang

10 min read

Testing And Logging NOS With Holley's Terminator X EFI System On A Foxbody Mustang

10 min read

When running power adders, Holley's Terminator X has two superpowers: wideband closed loop control and comprehensive data logging. To see how these two features help when using nitrous, we ran a 1991 Mustang GT equipped with Holley's Terminator X EFI system on the chassis dyno at Boost Addicts in Gallatin, Tennessee.

Older factory fuel injection systems used on vehicles like this 1991 Mustang use "narrow band" oxygen sensors that don't provide closed loop feedback during wide-open throttle. This is because during full throttle, the target air/fuel ratio is richer than the narrow band oxygen sensor's range. At wide-open throttle, the EFI system makes fueling estimates based upon readings from the other sensors and adds fuel based upon a predetermined "recipe" programmed into the factory EFI computer. This meant when running a power adder such as nitrous, the additional fuel needed had to be introduced by manipulating the fuel pressure regulator or injecting fuel via a nozzle or plate. Determining the right amount of fuel to add involved more estimates and testing.

However, the Terminator X's wide-band oxygen sensor monitors the air/fuel ratio continuously—even during wide-open throttle. Estimates are still used to set the baseline for the additional fuel, but even if your estimates are off, the Terminator X has your back. Checking the "Run Closed Loop to New Target A/F Ratio" option ensures that (if the fuel system is up to the task) the engine receives the desired air/fuel ratio.

Then, the Holley Terminator X's powerful data logging feature is a great way to double-check the results and make any adjustments.

Here's how Holley's Terminator X made spraying a 1991 Mustang GT a breeze.

Fox Mustang TermX Nitrous Tuning

We took this 1991 Mustang GT to Boost Addicts in Gallatin, Tennessee where it tickled their in-house Mustang chassis dynamometer with 193 horsepower and 265 lb-ft of torque.

Terminator X USB Link

With the baseline dyno run complete, we were ready to record a data log of a dyno run with the nitrous. With the Terminator X laptop software open, we clicked "USB Link" at the top of the window and then clicked the data log icon (clipboard) to start recording.

Dyno graph with nitrous

With the software recording data, we let 'er rip. Check out this dyno graph! With a 057 NOS jet, we picked up 112 horsepower and 138 lb-ft of torque to the wheels. That’s over a 50% increase from the naturally aspirated baseline. The torque hit was massive!

Terminator X fuel system log

After the run, we stopped logging and opened the log file to check the tune and verify our fuel system wasn't running short. First we compared the air/fuel ratio (AFR) target (yellow dotted line) to the actual air/fuel ratio (cyan line). Note that at 3500 RPM (red line), the nitrous system engages and the target AFR drops from 12.5:1 to 11.2:1. The actual AFR straddles the target throughout the run, which is what we want.

Terminator X injector duty cycle log

Next, we checked the fuel injector duty cycle (purple line). The injector duty cycle maxed out at 59%, meaning we had plenty of injector flow left. Since we had a Holley fuel pressure sensor installed (P/N 554-102) we could log fuel pressure (green line). Note that the fuel pressure doesn't drop throughout the run, indicating that our Holley 190 lph pump is keeping up with the fuel demand. Armed with this knowledge, we are ready to hit the track with confidence!


Wes Duenkel
32 Posts