DETROIT — Sales of classic cars — especially American muscle cars from the 1970s and 1980s — are showing unexpected strength in auctions so far this year, according to the president of the largest insurer of collectible cars and boats.

“That was when Detroit and other automakers got back to building great cars,” after a brief Dark Ages that coincided with the first oil crisis and the advent of emissions controls, says McKeel Hagerty, president of Hagerty Insurance.

He calls them “Bandit-era” cars, because the old road-trip comedy Smokey and the Bandit — starring Burt Reynolds, Sally Field and a Pontiac Trans Am — coincided with and added to resurgent interest in performance cars.

The January auctions include major sales in Scottsdale, Ariz., and Kissimmee, Fla. Sales and prices in Scottsdale were down slightly, but Hagerty calls Kissimmee “a barn burner,” up about 30% from 2015. Analysts had expected sales to fall due to global currency fluctuations, falling oil prices and unease about the Chinese economy.

That kept many collectors from offering cars for sale, on the assumption they’ll get better prices in a year or two, he said. Muscle cars have recovered from a crash in value during the Great Recession.

“They are driving the low and mid-market now,” he said. “Good, solid muscle cars are selling at rational prices that are determined by the rarity of the vehicle.” In the case of muscle cars that were built in the tens of thousands, that means cars with bona fide records of when and where they were built.

“Prices for cars from the ‘70s, ‘80s and ‘90s are showing the most growth,” Hagerty said, “particularly limited edition performance cars. Cars from the 1950s and pre-World War II eras are down.”

Part of the reason for that is that each generation tends to collect cars that were hot when it was young, including used cars that young people could afford to buy, customize and dress up.

“Generation X is finally coming into some money,” Hagerty said. They’re interested in cars that were relevant to their youth.” In addition to muscle cars, that means cars featured in TV shows like Miami Vice, Magnum, P.I. and The Rockford Files are hot.

There’s also a trend to higher prices for early sporty imports. Demand for the Nissan 240Z and early Mazda Miatas is strong, along with 1980s sporty compacts like the VW GTI, Audi Quattro and Toyota Supra.

Porsches of all eras are selling well, because the brand has always done a great job of managing production and connecting its road cars to the success of its racing programs, Hagerty said. “The brand has been on the rise for the last 24 months.”