They may not be Boy Scouts, but they have mastered the art of the pinewood derby.

More than 100 artists, amateur engineers, and spectators turned out to The Boiler art gallery on N. 14th Street in Williamsburg last week for Brooklyn Gravity Racers, an adult take on the classic Cub Scouts race, which is a micro version of the soapbox derby. The four-day event pushed adult racers’ craftiness to the limit with exacting rules and a packed lineup of veteran speed demons. The festivities coincided with the 20th anniversary of Pierogi, The Boiler’s parent gallery on N. Seventh Street, which has been hosting the adult pinewood derbies once every five years since the 1990s.

One participant said she relishes the races, more for the challenge and camaraderie than the competition.

The grown-up version of the derby bends the Cub Scouts rules a bit, allowing 10-inch long vehicles whereas the Scouts requires racers to carve their cars out of 6-inch blocks of wood. The ad hoc league also allows for cars heavier than five ounces, but places them in a separate “Heavy Weight” class, which this year featured an un-race-able 16-pound ride. Under the gallery’s regulations, only the featherweight buggies qualify for the coveted Speed Award. And, because these are artists we’re dealing with, there are two award categories for looks — Aesthetic, and What Were You Thinking.

But on some things, organizers hew as closely to the Scouts rules as a race car hugging a high-banked turn, keeping the width between wheels at a strict 1.75 in. and the bottom clearance at .375 in., which allows cars to traverse the wooden track without rubbing.

Cub Scouts race annually, but the adult derby only takes place twice every decade because it requires so much time, energy, and resources to organize without the backing of the Boy Scouts of America, Pierogi co-owner Joe Amrhein said.

“It is so much work to put this together, and we do it out of our own pocket money,” said Amrhein. “Once every five years seems to be the right number for us.”

This year racers submitted cars adorned with such odd accessories as syringes, bubblegum, and a bottle of water from the Gowanus Canal. The 16-pounder, made almost entirely out of brass, was a favorite of Amrhein’s.

“It was too heavy to be safe,” he said. “But I loved the way it looked.”

Ziegler used the same car that she made for the last Boiler pinewood derby in 2009, but she fine-tuned it by adding weights to the body and tinkering with the tilt of the wheels. She won her first race and came in near the front of the pack in four others, she said. The competition was stiff, she said.

“People take the engineering of these cars very seriously,” she said.

Amrhein is considering putting on races in other cities such as Los Angeles and Berlin to form an artsy, possibly international tournament circuit, he said.

“Having a race-off between cities seems like it would be a crazy and fun idea,” he said.