* California T model to debut at Geneva auto show
* Ferrari promises better performance in more efficient car
* Says will consume 15 percent less fuel than predecessor
* Reduces carbon dioxide emissions to 250 g/km from 299
GENEVA, March 3 (Reuters) - Italy's Ferrari has mounted a turbocharged engine on its latest supercar for the first time in more than two decades, as even luxury automakers are forced to seek ways to cut emissions without sacrificing performance.
The California T, which will debut at the Geneva auto show this week, will be equipped with an eight-cylinder engine that Ferrari says will consume 15 percent less fuel than its naturally-aspirated predecessor, reducing carbon dioxide emissions to 250 grams per kilometre (g/km) from 299.
By pumping air into the cylinders, turbochargers get more power from a smaller engine, sometimes at the price of sluggish initial acceleration. Naturally aspirated engines, which instead draw in air through a valve, can deliver more consistent torque and a bigger engine sound.
Unlike holdout Lamborghini and its naturally aspirated 5.2-litre Huracan on show in Geneva, Ferrari is breaking with tradition to offer its first turbo since the F40 coupe, sold between 1987 and 1992. The Fiat-owned sports car maker claims to have achieved "zero turbo lag" with new technology that adapts the torque curve to each gear change.
"The California T ... is one of the results of significant investment in product and technological innovation," Chairman Luca di Montezemolo said last month.
The new model can accelerate from 0 to 100 km/h in 3.6 seconds, Ferrari said, 0.2 seconds faster than the 2012 California. Pricing has not been disclosed, although it is not expected to be significantly higher than the tag of around 185,000 euros ($255,500) on the last California.
The Italian carmaker also said it had modified the car's exhaust to enhance engine noise, offsetting the turbo's muffling effect.
Fans of Ferrari - ranked the world's most powerful brand last month by consultancy Brand Finance - are optimistic.
Joe Adams, president of the Ferrari Club of America, said his members were excited about the prospect of getting more efficient horsepower and better fuel mileage out of the cars.
"Ferrari needs to be able to show its technical prowess," said Adams, who has owned seven different Ferraris over the years. "Being green is just another challenge and that's something Ferrari relishes."
The move by Ferrari coincides with the introduction this year of new Formula One rules requiring the use of turbocharged engines in the sport for the first time since 1988.
Fuel-efficiency improvements account for a large share of the 2 billion euros in planned research and development spending over five years, Ferrari has said.
The carmaker, which last year introduced its first hybrid, the 1 million euro LaFerrari, said its average CO2 emissions have already fallen 40 percent since 2007.
While supercars will keep emitting more than small family cars, they need at least to show improvement, said Jay Nagley, managing director at Redspy, an automotive consultancy. "They don't want to look like dinosaurs," he said.
Unlike Ferrari, Lamborghini is avoiding turbos for now and has no intention to pursue hybrids anytime soon. However, both technologies are readily available from parent Volkswagen should it choose to use them later.
The Huracan LP 610-4 on show in Geneva is Lamborghini's successor to its bestselling Gallardo model, which ended production last year. The carbon fibre and aluminum car's 10-cylinder engine emits an average 290 g/km of CO2.
"One thing that makes a Lamborghini so unique is the music that comes out of the exhaust pipes," said Nick Wirth, a fellow of Britain's Royal Academy of Engineering. "A turbocharged engine would make the orchestra a little bit quieter."
However, Wirth believes it is only a matter of time before even the most exotic brands are forced to embrace turbos and hybrids to meet tightening emission rules. "Ultimately, everyone will have to move in that direction."