1963 saw the Impala SS continue to increase in performance and popularity. With the elimination of the Bel Air coupe buyers again switched back to Impala SS coupes and convertibles. (Impala SS engine options included the 230ci 140hp I-6 283ci 195hp V-8 327ci 250 V-8 327ci 300 V-8 409ci 4 bbl 340hp V-8 409ci 4 bbl 400hp V-8 409ci 2x4bbl 425hp V-8 and the 427ci 2x4bbl 430hp V-8.) The 409 was further improved for drivability and a detuned version with 340 bhp was made available with an optional Powerglide automatic transmission. For the serious enthusiasts Chevrolet offered the 409 with solid lifters and a single four bbl carb good for 400 bhp and a solid lifter 409 with two four barrel carbs good for a whooping 425 bhp. As if that wasn't enough Chevrolet introduced a new engine the Z-11 in mid 1963. This was a 427 cid V8 loosely based on the existing 409 but featured a smaller bore and a longer stroke. It featured angled valves and was nicknamed the "porcupine head motor." Although it was officially rated at 430 bhp it easily made close to 500 bhp and was an instant success at the drag strip. Unfortunately it was only available to factory approved customers through Chevrolet's RPO (Regular Production Option). It was usually coupled with the optional factory fitted lightweight front end - aluminum panels and bumper. In addition Chevrolet was preparing another 427 V8 the Daytona "Mystery Motor" to be used at the 1963 Daytona race. However Chevrolet officially withdrew from racing competition putting a stop to development of the "Mystery Motor" and after only 55 Z-11 Impalas were built. The 427 would not reappear for another three years but it would be a direct descendent of the "Mystery Motor" that Chevrolet had killed in 1963. Prices ranged from $2661-$3170. Weights were approximately 3265-3870 lbs.
