Two of the most important cars to Peter Brock are set to go under the hammer at the end of May.

The racing legend's personal HDT Commodore and a one-off Opel Monza Coupe developed by his HDT Special Vehicles operation are the stars of this month's Shannons Sydney Autumn Auction.

The HDT Commodore is a Group 3 SS model built by Brock's performance division in the 1980s. Originally used for media events, Brock eventually took over the car and used it as his personal road car.

The car was bought by its current owner directly from Brock and comes with a letter confirming its authenticity.

Shannons expects the Commodore to sell for between $80,000 to $100,000.

The other star attraction of the auction is the Opel, the only example of the German coupe modified by HDT Special Vehicles.

The Opel Monza Coupe modified by HDT SPecial Vehicles will be auctioned in Sydney at the end of May. Photo: Supplied

Brock had plans to use the imported two-door as a future offering for his expanding HDT Special Vehicles business but the business case didn't add up to General Motors.

But this prototype was given the full HDT treatment including replacing the Opel's usual six-cylinder engine with the HDT 5.0-litre V8 paired with a five-speed manual transmission, HDT optimised suspension and even Brock's infamous Energy Polariser.

The Monza is expected to fetch up to $120,000 on the May 30 auction as collectors bid for a piece of Brock history.