The launch of Mercedes-AMG's One hypercar has been pushed back to 2021, according to a report from Auto Motor und Sport published Thursday.

The One was previewed in prototype form as the Project One at the 2017 Frankfurt International Motor Show and confirmed at the time for a launch in 2019. But getting the car's Formula One engine suitable for road duty—certainly no easy feat—is taking longer than expected.

Tobias Moers

Tobias Moers

AMG chief Tobias Moers last October said the One was delayed until 2020 due to challenges in getting its engine to meet emissions standards. That's the same reason cited by Auto Motor und Sport, whose source said AMG had underestimated the difficulty in converting the engine for road use.

Motor1 detailed in a Friday report that AMG's task has been made tougher by the WLTP (Worldwide Harmonized Light Vehicles Test Procedure) emissions standard coming into force in Europe from September 1, a tougher standard than the somewhat lenient New European Driving Cycle (NEDC) it replaces. To meet this, AMG is developing the One with multiple exhaust gas treatment systems, among other measures.

Mercedes AMG W07 Hybrid 2016 Formula One car power unit

Mercedes AMG W07 Hybrid 2016 Formula One car power unit

And even without the emissions issue, just getting the F1 engine to operate like an engine in a road car is a monumental feat in itself. Remember, this is an engine that normally has a team of engineers monitoring it around the clock. For example, because the tolerances of the internals are so tight, an F1 engine normally can't be started until it's warmed to a temperature of about 175 degrees F, achieved by circulating warmed coolant through the engine and radiators. The engine then needs to be manually turned so that all the oil can seep through before it's finally fired.

Given this, it's no surprise that the One's engine will only be rated to 50,000 kilometers, after which a rebuild will be necessary.

Mercedes-AMG One

Mercedes-AMG One

In case you've forgotten, the One features the actual engine used in AMG's multiple championship-winning F1 cars: a 1.6-liter turbocharged V-6 complete with an 11,000-rpm redline and a turbo-mounted electric motor-generator. Three additional electric motor-generators feature in the One, with one mounted to the engine and a further two at the front axle to form an all-wheel-drive system. Combined output is above 1,000 horsepower.

The same issues haven't plagued the rival Aston Martin Valkyrie, which uses a bespoke 6.5-liter V-12 developed by Cosworth. Prototype Valkyries are currently being tested and delivery of the first customer example is scheduled for late this year.