The chief engineer for the new 737 says the Boeing Co. has selected the optimum size for its new engine and will produce the most fuel-efficient and least-costly jet in the single-aisle market.

The engine for the 737 MAX will have a larger, 68-inch diameter fan and a lower weight, said John Hamilton, 737 chief engineer.

“The 737 is a more efficient, lighter design and requires less thrust than other airplanes in this class, which is important because weight and thrust have a significant effect on fuel efficiency and operating costs,” Hamilton said.

He said an airplane’s weight affects about 30 percent of its operating costs, so a smaller, lighter and more-efficient jet engine will help Boeing “maintain the current advantage we have” over its chief competitor, Airbus.

Airbus decided two years ago to add a new engine to its A320 single-aisle jet and received hundreds of firm orders at this year’s air show. Boeing followed suit and said Thursday that it now has 600 commitments for the new MAX, up from 496 when it launched the program in August. Hamilton noted the 600 “are commitments, not orders.”

He acknowledged that Boeing is behind Airbus in its re-engine program, the A320neo, but said there’s a lot of interest from airlines in Boeing’s model.

“It’s a huge growth market,” he said of single-aisle jets. “The customers are responding quite well, and we expect several hundred more commitments soon.”

Hamilton said the engine will be the largest change for the 737 MAX, but he noted several smaller ones, including:

•The nose gear will be longer.

•Tail cones will be more aerodynamic.

•The wing will be strengthened to handle the added load on the engine.

•The fuselage will be strengthened for the same reason.

•The engine computers will change.

•Fly-by-wire spoilers will be added.

Boeing said Thursday it continues to work with customers to see what they want in a new model aircraft. It expects to settle on the design configuration in 2013. The first flight of the new jet is set for 2016, with deliveries in 2017.

He said he expects to be pushed to beat that deadline, but said Boeing wanted to set one that it strongly believed it could meet. The company was more than three years late in delivering its new 787 jet.

The new 737 family will be powered by CFM International LEAP-1B engines, the company said. The new engine will use 10 percent to 12 percent less fuel than existing 737 engines and offer a 7 percent operating cost advantage over the Airbus A320, Hamiliton said.

It said in one year, a fleet of 100 will save 175 million pounds of jet fuel and save $85 million in fuel costs. Boeing said the amount of fuel burned should be 16 percent less than the competitors are burning now and 4 percent less than future offerings.

The MAX will also be able to fly farther than today’s 737s, which have 61-inch engines, according to the company. The A320neo has a 78-inch engine.

Hamiliton called the 737 the most popular and reliable commercial jet and said it has sold more than 9,000 of the Renton-built aircraft.

Boeing has not announced where it will build the new 737 model, although analysts say it would be difficult for it to meet its deadlines if it tries to build entirely new production facilities elsewhere.