Sales of the fastest road-legal car ever produced in Australia are in the slow lane.

GM Holden Ltd.’s Holden Special Vehicles unit said in December it was capping production of its W427 7.0L Supercar at 200 units, half the 427 vehicles planned when the model was announced earlier last year.

But now it appears even that number has not been reached, with HSV saying orders for the W427 will close at 5 p.m. April 28, “giving prospective owners (several) weeks to place an order for a piece of Australian motoring history and one of the finest cars ever produced in this country.”

“We announced late last year the last build for the W427 would be mid-2009, and we now need to confirm orders for the final build of the program,” HSV Managing Director Phil Harding says in a statement.

Harding cites rave reviews from customers, the media and motoring aficionados and says one Australian auto magazine recently described the W427 as belonging to a group of Australia’s top-10 most valuable cars.

The A$150,000 ($107,468) muscle car, a heavily modified version of the Commodore sedan, has a U.S.-sourced V-8 engine. HSV says the W427 achieves 503 hp and 472 lb.-ft. (640 Nm) of torque.