LOS ANGELES — High fuel prices have many business owners worried about their rising expenses and customers who have far less money to spend.

Then there is Gale Banks Engineering of Azusa, in the San Gabriel Valley east of Los Angeles, where the product line might be in even greater demand now than before. The company is part of the $285-billion aftermarket industry, which includes custom engineered automotive and truck equipment billed as better than factory parts.

When the industry sprang up shortly after World War II, speed was the mantra that drove enthusiasts to tweak their vehicles. Now, interested motorists are more likely to be owners of motor homes, large sport utility vehicles and full-size trucks who are desperate for better fuel economy.

President Gale Banks III said he helped customers get through the 1973-74 Arab oil embargo and the 1979 energy crisis. At his office, which is decorated with 50 years of automotive history, Banks leans forward as if sharing a secret.

"I actually like fuel crunches," Banks said. "I've been through two of them. Both of them gave me and this company direction."

But there are limits to the improvements he can deliver, Banks said, bemoaning the impossible promises from snake-oil-style ads found in some automotive magazines.

"P.T. Barnum was right about one being born every minute," Banks quipped. Banks' products focus on three areas.

Bigger air intake systems deliver more air to the engine to help it breathe better, serving as the rough equivalent of giving a smoker a lung transplant from a long distance runner. Bigger exhaust systems give that additional air a quick escape route. The third part is a small computer called a tuner that fits under the hood and acts as a kind of personal fitness trainer for the engine, telling it when and how to work most efficiently.

They range in price from around $115 for a replacement filter for an air intake system to around $1,700 for an intake manifold that delivers the air-fuel mixture to the engine cylinders. They also are sold as sets called PowerPacks.

The performance claims such as gains in fuel economy are modest by design, Banks said, based on something his father referred to as "the rule of 10 and the rule of 100."

Banks' father walked a beat as an officer for the Los Angeles Police Department but had come home from World War II suffused with knowledge on how to keep just about any kind of ground vehicle in good repair. It was know-how, and a way to approach business, that he passed on to his son.

"He'd say, 'Lie to someone about what something does and he'll be angry enough to tell 100 people. Tell him the truth, and he'll only be happy enough to tell 10 people, but those are 10 who might become customers,' " Banks said.

So, Banks claims his products can give a 10 percent or slightly better boost to fuel economy, while increasing horsepower and torque, the latter of which governs things such as towing and hill-climbing abilities. When there is a range of effectiveness, Banks says he uses the lowest result in the range.

"If I give him a high number, he'll be disappointed and wondering why he bought it. If I give him a low number, he'll be very pleased when he gets a better result," Banks said.

Banks Engineering employs about 200 people at its 12-acre campus of several buildings. Annual sales run about $16 million, according to Dun & Bradstreet, although Banks described revenue as in the "mid-eight figures."

Banks has become a legend among the aftermarket speed crowd, having set land-speed records and built what was once the world's fastest passenger car. He even improved the engine on the covert-action boats used by Navy SEALS.

His customers include big automakers and individual motorists who say that Banks' products have made their long drives easier and more economical.

Drag racer Tim Turner of West Harrison, Ind., who hauls his super-gas category vehicle in a trailer with a combined weight of 9,000 pounds, was getting a consistent 14.2 miles per gallon on his 2003 Ford F250 pickup truck before he bought a Banks Six Gun with a Power PDA — the names still reflecting the old hot rodder days. The air intake and exhaust systems give him more horsepower and an average of about 19.5 mpg, he said.

"Most definitely I was very shocked and very pleased that the mileage went up so much. And the power was more than what the factory advertised," Turner said.