By 1955 Chevrolet introduced its “small block V8” with 265 in³, not to be outdone Ford increased its displacement to 272 in³ and introduced the Thunderbird with a 292 in³ engine. The 272 in³ (4,465 cc) version of the Y-Block was the same bore as the outgoing Mercury 256 in³ Y-Block but with a longer stroke (3.625 x 3.3 in). The standard 1955 U-code featured a two barrel Holley carburetor and was rated at 162 bhp (121 kW) at 4,400 rpm and 258 lb·ft (350 Nm) at 2,400 rpm. The optional "Power Pack" M-code utilised a four barrel Holley carburetor and was rated at 182 bhp (136 kW) at 4,400 rpm.