Founded by Phil Ward over 25 years ago and recently owned by Tony Quinn, the ARC class was in March purchased by Brett Thomas’ TFH Racing entity, which also sponsors cars in the series.

A survey of competitors at the opening round in Sydney later that month resulted in a decision to drop Cragsted as the control engine builder for the 1251cc Yamahas used in the class.

While allowing teams to refurbish their own engines was well received on cost grounds, tensions rose during Round 2 at Symmons Plains last weekend over straightline speed disparity.

Amid accusations that some engines were running outside the regulations based on their performance, category management addressed competitors on Saturday.

A bold new plan was communicated that involved policing only the camshaft, carburettor and the original casing, essentially throwing away the rest of the rulebook as a way of levelling the playing field.

An official rule update delivered to teams on Tuesday clarified new regulations, which although far from being open slather, allows a capacity increase to 1347cc through a bigger bore size.

Other permitted changes include the allowance of aftermarket valve springs, pistons and sump baffles, all aimed at reducing costs.

The increase in engine capacity, though, essentially gives competitors the choice of spending an estimated $4,000 per engine to upgrade, accept being uncompetitive or withdraw.

Johnston Craill Racing Enterprises, a team co-owned by TV commentator Richard Craill, has already signified it will skip the upcoming round in Perth next month.

The team had already chosen to refresh its engines following the post-Round 1 decision to drop Cragsted and is now “in an extremely challenging position”.

“To change the regulations in a way that significantly influences engine performance – as an increase in capacity does – and requires a substantial financial input two rounds into a season is in our opinion unprofessional for a championship at this level,” read a note sent to JCRE partners.

“As we are not willing to represent our partners and supporters racing with little realistic chance of competing at or near the front, we are not planning on competing again until such time that we can enter with cars that are at the same specification as those already competing.”

JCRE also urged the ARC category to improve the policing of its engine rules to stamp out the alleged bending of regulations.

“We also strongly urge the category to ensure they have the mechanisms in place to properly check that competitors are abiding by these updated regulations moving forward,” it added.

“These rule changes have been brought on by an existing lack of compliance to the approved technical regulations, so we are hoping that with this change comes the scrutiny the category requires.

“We entered Aussie Racing Cars based on competing in some of the best wheel-to-wheel racing in Australia where driving talent was on display – not to race in a two-tier system where some have special engines and some do not.”

The category’s note to competitors confirming updated engine rules on Tuesday stressed it was acting in the best interest of competitors.

“Our commitment remains the same as it has been for over 25 years: to make decisions that benefit the category as a whole and to maximise participation opportunities,” it read.

“ARC’s philosophy is a tightly controlled, one-make category where driver skill – not budget –determines success.

“We are focused on fairness, maintaining a level playing field, and reducing engine costs through increased reliability and longevity.”

The category also reminded competitors that the control chassis, body work and ancillary components must remain “as supplied by ARC”, with no modifications allowed.