The team had initially agreed to freeze its engine specification for the Pirtek Enduro Cup on the understanding that the 70 percent ethanol fuel blend would be approved for the three events.
With V8 Supercars instead having elected to introduce compulsory pitstops, Erebus general manager Ross Stone told Speedcafe.com that the previous pledge is now “off the table”.
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The squad took its best ever finish of fourth in Sunday's Sandown 500 despite losing what it calculated to be 14 seconds in added pitstop stationary time due to its higher fuel consumption.
“There is a lot more we can do, it's all just a matter of time,” explained Stone, who says his engines are still lacking bottom end power, as well as economy.
“If we make any spec changes we need to make sure we validate it on Craig Hasted (V8 Supercars designated engine performance chief)'s dyno, and you soon start running out of time when you spend a couple of days here and a couple of days there doing all of that.
“We had some stuff that we've done on the (Erebus team) dyno nearly two months ago that we parked when it looked like E70 was going to be the short-term solution.
“We'll now get stuck in and see what we can come up with. We're going to give it a big go to introduce it for Bathurst.”
Having run an unchanged engine package at Sandown, Stone put the team's improved form down to suspension developments run at a pre-event test.
“We've done a lot of hard work,” he said.
“Before we went to Sandown we had a test at Queensland Raceway where, instead of getting temperatures under control and different bits and pieces, we actually did some suspension work.
“We knew we'd be reasonably strong at Sandown and we thought we'd put on a good show there.
“I think our cars will be quite good at Bathurst as well, but we'll have to wait and see.”
The team has cancelled a planned pre-Bathurst test in order to focus on its workshop activities in the lead-up to the event.
Nissan Motorsport, meanwhile, is expected to head into the season's biggest race with minimal changes to its package.
The team proved unable to crack the top 10 at Sandown, where its lack of top-end speed, as well as its poor economy, were both starkly apparent.
“We can't do much at all internally, we would have already done it if we had something there that's a good gain,” said Todd Kelly of the potential for upgrades ahead of the 1000.
V8 Supercars is yet to confirm the exact number of pitstops that will be compulsory at Bathurst, while Kelly still holds some hope for a late rethink of the E70's rejection.
“We've got to still go through that process and have V8s know what the fairest solution is, but I don't know that what we did at Sandown would be ideal for anyone,” he said.
“I think it's a shame to tamper with the Bathurst event (by introducing compulsory pitstops) to fix a problem with two teams that doesn't effect anybody else.”