The line of cars in front of Turn5's headquarters outside Philadelphia alludes to the business inside: souped-up Jeep Wranglers, Ford Mustangs and pickup trucks.

"Whoever knows about cars, we hire, specifically the cars we sell [parts] for," said Andrew Voudouris, 30, who with his older brother, Steve, 32, started Turn5 in 2003 in the basement of their parents' four-bedroom home.

The company provides aftermarket parts primarily for Mustang, Wrangler and Ford F-150 vehicle models through three e-commerce sites.

The sales niche is thriving so much that Turn5 — a take on racetrack terminology — will be moving this fall to premises twice as big. Its workforce is expected to grow from 425 to 1,000 in the next three years.

In the world of taillight tint inserts, axle-back exhausts and an indulgence called a Jammock — a heavy-duty hammock designed for lounging when the top of a Jeep is removed — consumer passion for souping up vehicles is hot and expected to get hotter.

"I just don't see an end in sight," said Andrew Voudouris. He added that Turn5 has been profitable from the start with "double-digit" growth year over a year, but he declined to provide specific revenue.

A study released earlier this year by San Francisco-based Grand View Research Inc. valued the global automotive aftermarket at $318 billion in 2015, projected to hit $486 billion by 2025.

The Voudouris brothers started their business selling computer parts. But in 2004 when they saw people complaining about the "old school" aftermarket parts business on online message boards, they shifted focus.

Customer service is where the brothers think they can outdo their most formidable competitor, Amazon, believed to be the auto aftermarket's largest single online retailer.

"We're super-focused on how we create a better experience for our customers," Steve Voudouris said. "At the end of the day, that isn't something Amazon will be able to do."

In March, Turn5 added a 40,000-square-foot distribution center in Las Vegas for faster satisfaction of orders from the West and Southwest. Last year, a 5,000-square-foot call center was added near Philadelphia.