Said grew up with motocross as his first motorsport passion. While attending the Detroit Grand Prix in 1985 as a spectator, he met SCCA champion Bob Sharp, an encounter that redirected his ambitions toward road racing. He began competing in the SCCA in 1987 and was named SCCA Rookie of the Year in 1988. By 1993 he was driving BMWs in the IMSA series, and in 1997 and 1998 he won the 24 Hours of Daytona and added the 1998 12 Hours of Sebring in the same IMSA campaign.
Said's business ventures ran parallel to his racing: he co-founded the apparel and action-sports brand No Fear, established Honda and Suzuki motorcycle dealerships in his twenties, and later opened a BMW dealership in Murrieta, California. He is also a co-owner of the K1 Speed go-kart racetrack franchise.
Said entered the NASCAR Craftsman Truck Series in 1995 primarily as a road-course specialist. He won his first Truck Series race at Sears Point in 1998 and added his first Busch Series win at Circuit Gilles Villeneuve in Montreal in 2010, leading the final laps after Robby Gordon ran out of fuel with three to go.
His NASCAR Cup appearances were concentrated at road courses. He was consistently competitive at Watkins Glen and Sears Point throughout the 2000s, scoring a best Cup finish of third at Watkins Glen in 2005 and fourth at the Pepsi 400 at Daytona in 2006 — his highest oval result, which he described as the highlight of his career. He qualified on the outside pole for the 2007 Daytona 500, eventually finishing fourteenth after surviving a late-race accident.
Said drove for several teams including MB2/MBV Motorsports, Evernham Motorsports, No Fear Racing (which he co-founded with crew chief Frank Stoddard), FAS Lane Racing, Go FAS Racing, and Circle Sport–TMG. He ran NASCAR road-course events intermittently through 2017 before announcing retirement after the I Love New York 355 at Watkins Glen that year, though he made further appearances in the Xfinity and Cup series in 2021 and 2022.
As a BMW Motorsport factory driver, Said captured the Rolex Sports Car Series GT drivers' title in 2004. In 2005 he became the first American to win the 24 Hours Nurburgring outright, co-driving with Pedro Lamy, Duncan Huisman, and Andy Priaulx in a BMW M3 GTR. He also won the Six Hours of the Glen in 2006.
Said won the 24 Hours of Daytona in the GT category in 1997 and 1998 and the 12 Hours of Sebring in 1998. He competed in the American Le Mans Series with PTG Racing and was listed on the 2011 24 Hours of Le Mans entry in the LM GTE Am class.
Said dominated Trans-Am during the early 2000s, winning more than 40 SCCA races across Trans-Am and IMSA over his career. He claimed the 2002 Trans-Am Series championship, winning all but four races that season. A 45-day suspension in 2003 for alleged unprofessional conduct interrupted his Trans-Am run. He returned to the series in 2019 and won at Road Atlanta in 2021.
Said competed in the Australian V8 Supercars L&H 500 at Phillip Island and the Bathurst 1000 in 2008 alongside co-driver Matt Neal. He returned for the Armor All Gold Coast 600 in 2011 with Paul Morris Motorsport. Said also appeared twice at the X Games, in rally car competition at the 2007 X Games XIII and in Stadium Super Trucks at the 2015 Austin X Games.
Said was a rare figure in NASCAR's modern era: a factory sports car champion and endurance race winner who competed on equal terms with the Cup regulars on road courses. His No Fear Racing venture gave him an ownership stake in a Cup operation. His son Boris Jr. is also a racing driver, making his Trans-Am debut at Road Atlanta in 2020.