The massive tax and spending bill passed by Congress earlier this month made a significant change to fuel efficiency regulations for cars and trucks that have been in place for nearly 50 years.

The Corporate Average Fuel Economy standards impose a fine on automakers whose fleets of cars and trucks fall short of the required miles per gallon. But under the “One Big Beautiful Bill Act,” that fine is now zero dollars.

That means that even with fuel economy regulations still on the books, carmakers won’t feel as much pressure to make their vehicles increasingly fuel efficient. And that may change what car companies choose to build.

Some of those changes have already started creeping into the automotive market. Take, for example, the 8-cylinder Hemi engine. The Hemi is not terribly fuel efficient, getting at best 21 miles per gallon in a recent truck model. But for years it was a big selling point for Ram trucks, thanks in part to a ubiquitous series of ads two decades ago.

Stellantis, owner of the Ram and Dodge brands, had recently been winding down its use of the Hemi. 

“The factory was still running, but they were removing it from model after model, and probably likely to shut that factory down in the next couple of years,” said Sean Tucker, lead editor at Kelley Blue Book.

The company was instead moving towards more fuel efficient engines and electric motors, in part to comply with federal and state requirements.

But then, shortly before Congress stripped away the financial penalties for violating fuel efficiency standards, Stellantis pulled a U-turn, announcing it will make more Hemis.

“The Hemi was about to go away, and essentially this gave it a new lease on life,” Tucker said.

It’s not the only company to shift back to large, gas-powered engines as Congress and the Trump administration roll back CAFE penalties and federal support for electric vehicles. In late May, GM announced it would make 8-cylinder engines at a plant near Buffalo, New York where it had previously planned to build electric vehicle motors.

But while these moves might mean more fuel-hungry trucks on the market soon, the overall mix of vehicles on dealer lots in the next few years might not change all that drastically.

“These automakers have to make decisions at least four or five years in advance, and in many cases, even more years in advance, eight years in advance,” said Kenneth Gillingham, a professor at the Yale School of the Environment.

Because car companies plan so far ahead, they can’t count on federal policy remaining friendly towards gas guzzlers. A future Congress might put those CAFE penalties back in place.

“In fact, they may be worried that the pendulum has swung so far in one direction that it might swing in another direction in just a few years,” Gillingham said. “If they're not prepared to accommodate that swing in the other direction, they could be in deep trouble.”

U.S. car companies also sell vehicles abroad, including in countries that have fuel efficiency rules that are getting more strict, Gillingham said.

“If they want to be making money around the world, and not just in the United States, they need to develop a fleet that can accommodate all of these many changes,” he said.

One way carmakers are trying to do that is by designing cars and trucks that can be outfitted with different kinds of powertrains.

Car companies have moved towards making “vehicles that could be produced with an internal combustion or hybrid system, or could be produced with a battery electric system,” said Stephanie Brinley at S&P Global Mobility.

Even if car companies are no longer being pushed by the government to make cleaner vehicles in the U.S., they could still be pulled in that direction by some consumers.

“The incentive for continuing to improve fuel efficiency and reduce emissions is consumer demand,” Brinley said. “It's better for the environment, and that is something that consumers care about.”

In the long run, most auto analysts still think that as electric vehicle technology improves, the industry will eventually go all-electric, said Sean Tucker at Kelley Blue Book. 

But for now, “if you're GM or Ford, you can earn quick cash by selling more of those big V8 powered SUVs and trucks,” Tucker said. “So I suspect that we will see the larger, less fuel efficient engines come back.”

Meanwhile, carmakers will still keep an eye on a more efficient, and electric, future.