The Blue Oval has been central to a parity push in the latter stages of development of the new Gen3 cars, voicing concerns over both aero balance and engine performance.
The aero is thought to have been solved during last-minute VCAT testing at Temora Aerodrome last week, the result of which is the addition of a flap to the front wheel arch of the Camaro.
The status of the relative engine performance, however, has been less clear, with sources suggesting that changes to mapping could be made once the season is up and running and data from competitive sessions is available.
Speaking on the eve of the season-opening Newcastle 500, Rushbrook confirmed to media that the question mark over the relative performance of the 5.4-litre quad cam Ford and the 5.7-litre pushrod Chev remains.
"On the powertrain side, engine and acceleration we knew at the beginning with different engine architectures that it was going to be a challenge," said Rushbrook.
"Instead of two pushrod engines with the same displacement, they have different displacements and technology. You can always meet on a dyno… but how they perform in the car can be different.
"So while there is equivalence certainly on the dyno, that manifests itself differently in the car, so some adjustments have been made in the calibrations that are in the cars to account for that and we’ll see how it works this weekend.
"But I think everyone is going into it with the right mindset that we’ll see how it works this weekend and certainly if further adjustments need to be made, then they can be. There is a process for that which will be driven through data, and is transparent and collaborative."
Rushbrook also clarified that there is no firm expectation that the Chevrolet unit will outperform the Ford motor this weekend thanks to some mapping changes that followed the all-in test at Sydney Motorsport Park a fortnight ago.
“We think we’re in a good place coming into this weekend but we don’t know what we don’t know, and as we get more data we’ll see what it is," he said.
“There were some small calibration differences that were done to address some idle issues which wouldn’t affect performance. The performance element of it was the same as what had been run on track in Sydney and then some small adjustments to address the acceleration differences."
Rushbrook also thanked Supercars for its work on the aero re-test, which he feels was crucial for the aero parity.
"The amount of work and effort that has gone into this is significant and I think it’s important we launch this series, the start of racing, in the right way," he said.
"So when we looked at aero, the testing that had been done, there were certainly some questions that came out of November from the testing that was done then and it was very good that the series, with all of the stakeholders in agreement, agreed to go back and do extra robustness testing and to get to where we are now.
"And I think very clear aero parity."
Rushbrook's support of the additional aero work followed comments from Jamie Whincup, head of GM homologation team Triple Eight, suggesting Ford had delayed the homologation process unnecessary.
Whincup told Fox Sports that, as far as he's concerned, parity was achieved in the initial VCAT last November.
GM and Supercars are understood to have both been happy to sign off on the aero after that test, with Ford the missing piece of the puzzle.
“We achieved [parity] in VCAT 1,” Whincup said.
“That was proven at VCAT 2, because there was one small change made to the Camaro — we’re talking four or five kilos of downforce or drag; we’re talking very, very small numbers and small percentages.
“Unfortunately we just had to talk about it and go around in circles for the months in between [November] and yesterday to get sign-off from Ford on the car to start racing.”
Practice for the Newcastle 500 kicks off at 11:15am local time tomorrow.
