The Braeside outfit has been holding out for Supercars to reveal its technical package changes before electing to lock in its plans for next season.
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A move to Ford Mustangs now seems increasingly likely after the championship confirmed its new engine regulations will see cars drop approximately 15 horsepower, by using a cheaper piston ring and rocker specification.
Supercars has also confirmed that the use of drive-by-wire technology will be optional.
Kelly was banking on the system being mandatory to save his team money through decreased wear and tear on engines, and allow the squad to move to a road car cylinder head.
The Kelly Racing boss noted that mandating electronic drive-by-wire would also help Supercars ensure parity engines across the grid.
“I've had a lot to do with the engine stuff in particular and everything was looking really good for how all the testing and everything's progressed with the rockers and the drive by wire and bits and pieces, and for some reason part of it got derailed, which was the drive-by-wire,” Kelly told Speedcafe.com.
“It is a little bit frustrating, because that was a big chunk of future-proofing the series from an engine perspective, and saving a considerable amount of money.
“So it's a bit sad that that's gone that far, and then it's become optional instead of mandatory.
“The way these cars hit the limiter in some places, the shock that goes through the whole driveline into the transmission and everything, it's ridiculous.
“And we could've pulled the throttle back instead of being in the hard cut so the (saving of) wear and tear on the cars alone would've covered the expense of the implementation, not to mention being able to homologate and paritise the engines off it.
“Now we're in the position where, with teams changing the rockers, if they don't quite meet the number, everyone's going to spend a heap of money on R&D again, which is pointless for the fans. They don't know the difference, and (it's) not sustainable for the teams.
“It's affected our engine plan a little. That changes our options significantly because we would hope to, if we were going to run the Nissan again, go back to the road car cylinder head that we started with.
“But without the equalisation of the drive-by-wire, we can't afford to spend that money.
“If it falls five horsepower short, we'll spend another 12 months with an engine that's not on the money and a heap of resource to develop it. The engine's good now, but the cylinder heads that we're using, we've almost used all of our stock up.”
Kelly says the team aims to decide if it will abandon its ageing Altima that debuted in 2013 for a Mustang over the next few weeks.
“In the next couple of weeks we'll really need to work out what we can do,” he added.
“We've almost got a cylinder head project complete to understand where we'll get to, yeah, so it really depends on the engine situation now.
“It'd be a Ford, if we had to change, just because of their business model of being able to purchase parts or make your own parts and whatnot and obviously they're extremely competitive.”
Should the team move to Mustangs, Kelly admits it would be difficult to find the funds to make the switch and continue to run four cars, which could see the operation scale down to a two car team.
Fellow Kelly Racing driver Simona De Silvestro is thought to be heading overseas while team-mate Garry Jacobson's options are unclear at this stage.
“Well, if we need to change manufacturers and engines, four cars is a big investment, so that'll be hard. That'll be hard to try and find the funds to do that,” he said.
“If we're not going to change, it'd be easy to continue with four, but if we are, it'd be very difficult.
“It all depends on what happens with the engine thing and what (car) we go to.
“But we need to make a call in the very near future to action any of the above.”