BEVERLY HILLS, California -- Women have salivated over Vin Diesel's ripped abs, bulging biceps and chiseled physique -- until now, that is.

The normally ripped action star underwent a massive transformation, packing on 30 pounds and adopting a Donald Trump-like hairpiece, for his role as a wisecracking mobster with a heart of gold in the new dramedy "Find Me Guilty," out Friday.

Helmed by multiple Oscar nominee Sidney Lumet ("Network," "Dog Day Afternoon"), the film is a true tale of New Jersey mob boss Giacomo "Fat Jack" DiNorscio, played by Diesel. Without any legal training, DiNorscio opted to act as his own lawyer during a criminal trial which, at 21 months, ended up becoming the longest mafia trial in U.S. history.

"One of my reservations in the beginning was that I didn't think I could look like Jackie DiNorscio," the "Chronicles of Riddick" star said recently of his rotund Italian alter ego. "I said to Sidney, 'How am I going to look like Jackie?' and he said, 'We have ways.' "

Lumet hired one of the industry's highest-regarded makeup artists to transform the youthful-looking 38-year-old into the weathered crime boss. But despite enduring two hours of daily makeup preparation, Diesel -- who eschewed prosthetics for the sake of authenticity -- still had to pile on the pounds to fully achieve his hefty new Mafioso look.

"I said I don't want to wear prosthetics because that'd be cheating," Diesel said. "I really had to gain the weight, so I would eat a quart of ice cream a day and not train at all."

"I think it was so incredibly refreshing because I had always been so conscious of my physicality and staying in shape, so to go the opposite way was fun for me. ... I was extremely proud of the fact that I sort of transformed myself, so I'd walk around the set and show off my stomach to everybody!" he recalled, laughing.

"Find Me Guilty" also stars Linus Roache ("Batman Begins") as prosecutor Sean Kierney, who paints DiNorscio and his 19 cohorts as vicious, callous criminals. The clan, headed by Alex Rocco of "The Godfather" fame, faces 76 counts of various charges, including racketeering, robbery, bribery, extortion, drug trafficking and money laundering.

The project was a full-circle experience for Diesel, as Lumet was the man who inspired the budding actor/director to direct his own short film, "Multi-Facial," in 1999. It was that 20-minute clip that got the attention of Steven Spielberg, who tapped Diesel for the war drama "Saving Private Ryan."

"Sidney Lumet was the main reason why I had to do this film," Diesel said of his 81-year-old mentor. "As an actor, it's a dream come true. Who else could you work with who has worked with actors you've grown up admiring, like Marlon Brando and Al Pacino?"

Under Lumet's guidance Diesel was able to break out of his stereotypical action-hero mold and deliver a noteworthy dramatic and comedic performance as DiNorscio, whose larger-than-life persona forced Diesel to step out of his comfort zone.

"[But] what Sidney would do is he'd create a whole environment, a whole reality that protects you as you delve into this character," Diesel explained. "I think sometimes you can give the best performance in the world, but if your director hasn't protected you [in that way], it takes away from the scene and it doesn't matter who was great or not."

Check out everything we've got on "Find Me Guilty."

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