From the IMDB's
trivia section for
The Car.
"There were six Cars built for filming by Barris Kustoms in Lynnwood, California: one main car of steel and five fiberglass replicas. Three replicas were destroyed in the climactic explosion scene and the other two replicas were wrecked in rollovers. The gloss-black main Car is a custom Lincoln Mark III with a locked 4.11 differential (to allow easier spinning), heavy-duty suspension, roll bar, safety harness, and amber-tinted glass. The top is lowered and the beltline raised. Twelve craftsmen built the main Car in six weeks."