The Indian team completed its first test of the Gen3 car, which has 100kW more power than the current Gen2 machinery, on Thursday with Oliver Rowland conducting driving duties.
Mahindra will take its Gen3 car to Goodwood's famous hillclimb event next week, where the machinery will make its first public appearance on track.
Heidfeld, who is Mahindra's test driver and ambassador, held the Festival of Speed record for 20 years after setting a 41.6s time on board a McLaren MP4-13 back in 1999.
But the German lost the record to Romain Dumas' run in the Volkswagen ID.R in 2019, which was clocked in at 39.9s to ensure an electric car could collect the record.
“It’s a proud moment for us to take this car to Goodwood just a week after its first test," said team principal Dilbagh Gill.
"This is testament to the hard work, determination and passion of the team to always push to achieve what others see as unachievable.
"I’m very much looking forward to seeing the car make its debut at an iconic event such as Goodwood, representing the whole of Formula E as the series takes a step to its new era in 2023.”
NIO 333 Gen3 test "productive" - Turvey
Oliver Turvey got his first taste of NIO 333's Gen3 machinery, suggesting that it will be "a fun car to race" when it makes its debut next season.
The Brit also relayed his experience of the reconfigured braking system, where the motor at the rear handles all of the braking at the back of the car, with the front brakes also augmented by a regenerative motor.
“It was a proud moment to be the first to drive the NIO 333 ER9 Gen3 car this week," said Turvey.
"Everyone in the team has put a huge amount of effort in to get the car ready, so it was great to have a productive test.
"The acceleration on 350kW is a decent step forwards and will be quick on the street circuits we race on in Formula E. It was also pretty cool to use the electric motor on the front axle for braking and to experience the full 600kW regen capability.
"It’s certainly going to be a fun car to race and I look forward to getting into the car again."
