When I think of what is termed muscle cars, I think of the US, especially the 1960's. They are not the sort of car I have had much to do with and they were never that popular in NZ. So some of you dear readers will more au fait with them than I am. What I can offer is a bit of insight and data.
Ford Mustang: I loved the look of the original model which went from 1963 to 1973. Sales were initially huge but soon settled at a more modest level. The peak of US sales was 540,800 in 1966 but down to 120,500 in 1972. I collated production numbers which can be seen by clicking here. That data would include exports.
In 2020, sales were 61,000 which is a far cry from initial sales but reflective of recent trends toward less cars and more SUVs. 2020 was a poor year for car sales anyway so it will be interesting to see if any sort of rebound will happen in 2021.
Dodge Challenger: This is a harder model to follow historically. it's first full year of sales was 1970 and that only reached 54,000 units. It went down from there and ended in 1974. The second generation surfaced in 1978 and ended in 1983 but was a rebadged Mitsubishi so not a US muscle car.
Then it returned in 2008 as the real deal and has continued since then. It currently outsells the Camaro, which I find surprising, given the size of the respective companies. 53,000 sales in 2020 was a fine result, not that far removed from the 2019 total.
Chevrolet Camaro: GM reacted to Ford's pony car with the Camaro. Its 1967 sales total of 206,000 wasn't a bad effort but like the Mustang it fell away pretty quickly. Only 45,000 found buyers in 1972. It has continued through to today, with only a break from 2003 to 2008. Production numbers can be viewed by clicking here.
As sales couldn't even reach 30,000 for 2020, it was a sad result. While GM has apparently committed to producing the model until at least 2026, beyond that who knows?
GM also ran the Pontiac Firebird and shared its platform with the Camaro. It ran from 1967 to 2002 so doesn't feature in the data below.