1958 Pontiac Bonneville Sport Coupe
For 1958, the Bonneville became its own model line rather than a performance upgrade within the Star Chief series, and a new two-door hardtop Sport Coupe joined the convertible, giving buyers a second body style in what proved to be a one-year-only design.
Both models rode on a new X-member cruciform frame that permitted coil springs at all four corners, replacing the semi-elliptic rear setup of the previous chassis. Placement on the 122-inch wheelbase gave the Bonneville more responsive handling than its size suggested.
The 370 CI “Tempest” V-8 (bored out from the 347 CI unit used in 1957) was offered in three configurations: a four-barrel at 255 HP, a Tri-Power three-carburetor setup at 300 HP, and Rochester fuel injection at 310 HP.
A Tri-Power convertible was chosen as the 1958 Indianapolis 500 Pace Car. Fuel injection, priced at $500, found only around 400 buyers before being discontinued mid-year, leaving the Tri-Power as the preferred performance option for most buyers.
Sport Coupe production reached 9,144 units, all in this single-year body. By 1959, the entire full-size GM lineup was redesigned under the Wide Track program, making the ’58 Bonneville a notably brief chapter in the model’s history.
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