The basic formula for rock hasn’t changed much over the past half-century or so: Take two or more teenagers, add drums, microphones and guitars, combine in garage and plug in. It doesn’t always work, but when it does the results can be mighty and long-lasting.

Drummer James Raymond and a friend — a vocalist who declines to use his family name professionally; his stage name is Relentless — were 14 when they started their band in a backyard shed at Raymond’s family home in Rutherford.

“We weren’t very good,” Relentless recalled. “A lot of the kids were rough on us. People said we wouldn’t make it.”

Twelve years later, Vengince has vanquished its early critics. The group has toured 40 states, gathered more than 3,100 registered fans to its Myspace.com page and sold some 7,000 CDs without a record label.

But at home in Napa County, the band is still practically unknown.You won’t hear the newest Vengince single, “Caskets and Coffins,” on local music shows, and the group plays only one or two Napa gigs each year.

“This isn’t popular music,” said Raymond (band name Flatline), describing the Vengince sound as “metalcore: We’re heavy metal and we’re hardcore.”

In other words: not exactly the type of band that gets booked to provide background music at wineries and restaurants.

Rare local show

A rare Napa appearance at Downtown Joe’s Sunday will give local fans, friends and family a chance to hear Vengince live without hitting the road – or paying for a ticket.

A Web video of the band, performing its song “King to Rat” at the Warfield in San Francisco last January, gives a compressed hint of the energy Vengince unleashes in concert.

Relentless — a towering presence at 6’ 4”  — prowls the stage, roaring lyrics like “Becomers, portray your image/Turn a nation, into a nightmare.” Massively amplified, his voice sounds like an angry oracle warning humans to change their ways.

Flatline’s precision drumming pierces intricate layers of guitars and electronic samples, while in the audience a seething “mosh pit” of shirtless, tattooed young men jostles happily to the music.

Will a mosh pit break out at Downtown Joe’s next week? Unlikely, Relentless said. Vengince fans packed the slim Main Street venue last June, leaving no room for moshing.

Still, the Dec. 10 gig promises sensations seldom known in downtown Napa, including the presence of “Jager Girls.” They’re young models hired to promote — without actually drinking — Jagermeister, the European herb liqueur. (Think of the “booth babes” seen at boat and auto shows, and you’ve got the general idea.)

Vengince became a “Jager band” after Relentless lived up to his name, submitting his band again and again for one of the company’s regular metal sponsorships.

“I just bombarded them,” he said.

His persistence paid off: Jagermeister helps promote the band’s appearances with posters, CDs and Jager Girls, giving Vengince much-needed support and helping to recruit new fans at concerts with more-established metal groups. In return, Vengince helps keep the venerable German brand at the bleeding edge of metal culture.

A rising tide for metalcore?

In person a thoughtful and soft-spoken 26-year-old with a business degree from Sonoma State University, Relentless splits his time between Vengince and the even-more-brutally-metal group Endrah, which is signed to a European label.

His day jobs have been casual, and he’s planning to give up his Napa residence in about a month and stay with friends when he’s not on the road.

“The time’s now,” Relentless said: The metalcore genre, with its emphasis on technical musicianship alongside the explosive energy of hardcore, has never been closer to a mass audience.

Metalcore bands snagging major-label record deals include the Boston, Mass., group Unearth — a paragon to Raymond and Relentless:

“They quit their jobs; they’re making it as professional musicians,” Raymond said. “We’re hoping to follow in their footsteps.”

He added, “I don’t want to be on my deathbed saying, “I wish I’d done this.”