Cars began queueing before dawn to be inspected, with hundreds of car trailers, tow cars and 4WDs of all makes and sizes.

Many had driven thousands of kilometres - from Perth, Queensland's far north, South Australia and Victoria, through floods and scorching heat - to the nation's capital to participate in Australia's longest-running modified car festival, held over four smoke-filled, busy days inside Exhibition Park.

In terms of attendance, it's the ACT's second-largest event behind the month-long Floriade. But it's a fiercely intense four days, and without a flower in sight. Vehicle entries were sold out months ago and around 120,000 people are expected to attend.

For Col Statton, chief scrutineer for the event, simply getting all the vehicles through his team's three double-laned assessment bays and into the show will be a massive achievement in itself and worthy of a few quiet celebratory beers once the rush is over.

"We began setting up the scrutineering bays on Monday, opened up early Wednesday and hopefully we should have everyone through here by Friday morning," Mr Statton said.

"Some of the entrants with road-registered cars have filled out their self-declaration and so getting them through scrutineering and away only takes five or 10 minutes.

"But there's a lot of modified cars which are trailered in so we go over them more closely checking primarily for safety items, things like having secure batteries, accelerator return springs, working brake lights, seat belts and that any modifications are safe and secure.

"We also look for fluid leaks, that wheel nuts are tight and make sure the drag and burnout cars have fire extinguishers. But generally speaking, there's very few issues; most of these people really look after their cars."

The elite show cars were identified as they rolled through and were redirected out to a special pre-judging bay at the back of the stadium. More than half the elite entrants sadly won't make the cut on quality, and miss out on a place among the top 60 which will be assessed even more closely again later.

It's a busman's holiday at Summernats for Mr Statton, who is the service manager at a Honda dealership in Canberra and takes his personal leave to work as chief scrutineer across a variety of car shows, including CentreNats in Alice Springs and Rockynats in Rockhampton.

"I do this because I just love the cars and the people are great; there's lot of regulars every year and you always enjoy seeing the new builds come through that people have been working on for years," he said.

For decades, scrutineering for Summernats had been held at the Thoroughbred Park racecourse. But the number of entrants - with the sold-out sign on entries going out mid-year - has overwhelmed that venue and for the first time, switched out to Bruce.

But even the huge AIS carparks were brimming with vehicles on Wednesday, the queues stretching down Haydon Drive and Battye St, with the big mega-buck tow rigs almost as impressive and expensive as the vehicles on behind.

Among those lined for inspection were Leah and Blake Poiset, from Camden, who are bringing their four kids and their red VK V8 Commodore to the festival.

"This is our 10^th year and this is our annual holiday," Ms Poiset said.

"We will be at skid row and cruising around."

Summernats entries generally are dominated by Australian-built Holdens and Fords, together with US muscle cars and the occasional Japanese-built vehicle. But there's some unusual machinery in the mix, too, including a Suzuki Mighty Boy and a NASCAR racing truck.

Gates open at 11am on Thursday, with the annual City Cruise at noon.