Porsche AG has put the idea of building a 21st Century version of the legendary Porsche 550 sports car back “into the desk,” CEO Matthias Mueller says.

Mr. Mueller had earlier this year floated the idea of a new Porsche sports car that would be priced below the brand’s Boxster and Cayman models. The original 550, produced in the 1950s, was a low-slung open-top car embraced by racers and celebrities, including actor James Dean.

However, in an interview Wednesday ahead of this week’s Los Angeles Auto Show, Mr. Mueller said that after studying the concept of offering a less expensive sports car now, he concluded “the risk to the brand is pretty high.” So the idea is now off the table, he said.

Still on the table, Mr. Mueller says, is the idea of a “sport turismo” – you could call it a wagon – version of the Porsche Panamera sedan. Plug-in hybrid versions of the Panamera are on track to go on sale next year, as is a plug-in Porsche 918 sports car. Plug-in hybrid Porsche Cayenne SUVs are scheduled to be available in 2014, Mr. Mueller said.

Mr. Mueller expressed some impatience with the emphasis on electric and plug-in cars, which has become traditional at the LA Auto Show, partly in deference to the pro-electric car leanings of California clean-air regulators.

“It’s a pity we are always discussing plug-ins and BEVs (battery electric vehicles,” he said.

More significant to the cause of reducing greenhouse gases and petroleum consumption are the improvements in internal combustion engines, Mr. Mueller said. He cited as an example Porsche’s redesigned Cayman sports car, on display in LA this week.

It’s new six cylinder engine is more fuel efficient than its predecessor – the 2014 model is rated at 32 miles per gallon on the highway compared to 30 for the outgoing car – but should reach 60 miles per hour from a standing start in 5.1 seconds, 0.3 seconds faster than today’s Cayman.

Porsche, now controlled by German auto giant Volkswagen AG, expects record sales in the U.S. for 2012, and Mr. Mueller said he’s confident the brand will achieve its goal of selling 200,000 vehicles a year worldwide by 2018, up from just under 117,000 vehicles in 2011. A big part of that increase will come from a new, smaller sport utility vehicle called the Macan which goes into production next year, he said.

“It’s a calculation,” Mr. Mueller said of the 2018 sales target. “Not a goal.”