For all the details, read his full explanation of how the Lap Times are tested.
The performance of all the vehicles in the Muscle class has been accurately tested by Broughy1322, a famous car tester and skilled driver who raced each vehicle around the same circuit and recorded their best lap times.
On this page you find the full list of the best Muscle Cars in GTA Online and GTA 5, ranked by their Overall Performance when raced around a lap.