Major changes have come into effect allowing classic car owners in South Australia to modify their cars and still access cheaper registration.

The limited registration scheme allows cars to be driven up to 90 days a year at an annual cost of about $90.

Previous rules meant cars could only access that scheme if no modifications had been made, including additions such as air-conditioning and improved braking systems.

Transport Minister Stephen Mullighan said the changes should see thousands more classic cars on the road.

"These are people that love their cars, that spend thousands or tens of thousands or sometimes hundreds of thousands of dollars, to restore them, to upgrade them, to make sure they're roadworthy, to make sure that future generations will see these parts of South Australia's motoring history," he said.

"It was a no brainer in the end for the Government to get in behind them."

Steve Smith has seven cars that he hopes to get on the road now that registration changes have come into effect.

"It'll be the best thing the state's ever had," he said.

"It'll allow people to get their cars out that they've got hidden in sheds, people who had got three, four, five, even more cars, they can register them and at least they can drive them around without having any problems of what cars are registered in what year."

Regular registration costs can be up to $846 for six-cylinder vehicles.

Cars with major modifications such as engine upgrades or major structural changes will still be required to undergo safety inspections and get relevant approvals to gain access to the road.