According to sources the Mustangs were split between a 30 millisecond and 50 millisecond shift cut for the 90-minute session.
All Fords had been running 50 milliseconds, already considerably shorter than the Chevrolet V8, heading into the Perth round.
Todd Hazelwood (Blanchard Racing Team), Cam Waters, Thomas Randle (both Tickford), Chaz Mostert (Walkinshaw Andretti United) and David Reynolds (Grove Racing) all ran the faster of the two cuts.
According to one leading driver the difference on the data was negligible.
All cars will now revert back to the 50 millisecond cut for the remainder of the weekend.
The shift cut experiment comes as part of a mapping change made to the Fords for this weekend in the ongoing search for parity between the Ford and Chevrolet hardware.
Ford Performance has been lobbying for changes based on the idea that the Chevrolet V8 has better throttle response and performance from fourth gear onwards.
The mapping change is mostly focussed on throttle response.
Reynolds topped yesterday's practice session, although all drivers canvassed by Motorsport.com indicated that the mapping change wasn't noticeable in the car.
The Perth SuperSprint continues with qualifying 11:10am local time today.
