In a refurbished factory tucked below Snyder Avenue in South Philadelphia, 48 naked railcars are being formally dressed for their public coming-out later this year.

Gleaming stainless-steel bodies are slowly being filled with wiring harnesses, heating covers, lights, doors, and seats. Soon they'll be adorned with the familiar SEPTA logo and rolled out the back door to try out their new wheels on a test track.

Then they'll get their real baptism of fire - carrying commuters who have been clamoring for years for relief from overcrowded, outdated, worn-out Regional Rail cars.

These are the first of 117 Silverliner V cars being assembled for SEPTA at the South Philadelphia plant by Hyundai Rotem USA Corp., a division of South Korea auto manufacturer Hyundai Motor Group. Three pilot Silverliner Vs were built in South Korea, delivered earlier this year, and are now being tested by SEPTA.

The 120 new Silverliners will replace 73 railcars built in the 1960s. SEPTA's rail fleet now has about 350 cars; with the retirement of old cars and the addition of new ones, the authority will have about 400 by next year.

After years of delays, SEPTA passengers are about to get their new rides. And Hyundai is getting a foothold in the United States, hoping to use the Philadelphia plant to build cars for transit agencies around the nation.

Hyundai Rotem has a contract to assemble 75 cars for Boston's MBTA at the refurbished Weccacoe Avenue factory in South Philadelphia. Plans to assemble 121 bilevel railcars for the Southern California Regional Rail Authority's Metrolink have been scratched; most of those cars will be assembled in Colton, Calif., to save time and money, said Doug S. Dan, senior vice president of sales and marketing.

With a total price tag of $274 million, each SEPTA car costs nearly $2.3 million. But Dan said Hyundai Rotem was losing money on the deal.

"This is our first project in the U.S.," Dan said. "We made the pricing to cover the costs at the time, but certain costs were underestimated."

Dan said the South Korean firm expected the investment here to pay off by giving the company a chance to tap into the vast U.S. market.

"We're committed long-term," he said, noting that the company had leased the South Philadelphia site till 2017. "This is a very important strategic location for Hyundai Rotem. We need a volume of work to maintain the workforce here."

He said the factory had the capacity to assemble about 200 vehicles at a time.

The plant now employs about 110 workers, including 20 administrators from South Korea. The American workers include engineers, electricians, mechanics, and laborers.

The steel car shells were made in South Korea. As required by law, the cars must be assembled in the United States and 60 percent of the components must come from U.S. sources. In this case, that includes brakes from Spartanburg, S.C., batteries from Cherry Hill, wheels and axles from Morton, and heating and cooling systems from West Chester.

As the plant speeds up its assembly process, from the current 18 weeks to 14 weeks, it will eventually employ about 200 workers, said Jun-Yeon Jung, senior manager of contracts administration and sales.

The new cars will have wider doors, wider aisles, larger windows, electronic destination signs, automatic voice announcements of station stops, and public-address systems that can be accessed from SEPTA's control center.

However, they won't have restrooms, and they will not eliminate the three-passenger seats that rankle many riders now.

A still-unresolved issue is the design of the engineer's compartment. The new cars are being built with cabs similar to those in many subway cars - extending halfway across the front of the train.

SEPTA engineers want bigger cabs that extend all the way across the front of the train, similar to those in the current cars.

Dan said the Silverliners would be delivered with half-cabs. But he said they could be modified later to accommodate full cabs if that's what SEPTA decides it wants.

Behind the plant, Hyundai Rotem has leased 1,500 feet of CSX track to test its cars. The Silverliners are designed to accelerate and brake more quickly than the cars they replace.

The first cars will be ready for the test track by June, Dan said. Once SEPTA accepts the three pilot cars, the first production cars can begin to go into service.

By late this year, commuters may be riding in the cars now being outfitted on the South Philadelphia assembly line. As the first cars roll out the door, Dan said, Hyundai Rotem will be looking for new opportunities in the efforts by the Obama administration to develop a high-speed rail industry.

The company builds high-speed trains in South Korea for that country's rail network and it could bring the same design to production here, he said.