the Z11

when the Z11 debuted in late 1962, it was a dichotomy of firsts and lasts for Chevrolet's drag racing efforts. It was the last of the full-size lightweights, thanks to GM's 1963 self-imposed anti-racing edict, and it ran the last W-headed race engine, but it was the first to possess the magic cubic-inch displacement - 427.

Built in three batches, the initial 25 Z11 Impalas were released on December 1, 1962. The first car arrived at Ammon R. Smith Chevrolet in York, Pennsylvania, near Christmas 1962, for the already highly successful team of Strickler and Jenkins, who had first met at a nearby drag strip years before.

Under the hood was a revised W-series engine. The stroke was increased from the 409 by .150-inch using a forged-steel 3.65-inch stroke crank to make it a 427, while the bore remained at 4.3125 inches. Forged connecting rods were employed, and forged domed pistons pushed the compression ratio to 13.5:1.

Factory-designed cast-iron headers were installed, but were generally quickly swapped out for steel-tube headers. The aluminum water pump, fuel pump, lines and filter and the rocker covers were also specific to this engine, and a deep sump oil pan was used. The 427 was underrated at 430 hp.  It ran 10.90s at 128 MPH,

Jenkins painted the engine semi-flat black to dissipate heat more quickly. Though the Z11s were delivered with an alternator, he installed a generator with a quick disconnect wire and a short belt from it to the water pump. This allowed him to run the generator as an electric motor to turn the water pump and circulate the water to cool the engine when the car was shut off.

He also painted the underside of the car and the suspension white. His reasoning was said to be to reflect the rising heat from the track and also to make it easier to see while working on the suspension.

A complete race package, the Z11 didn't rely on the powertrain alone to get the job done; there was a weight reduction plan, too. An aluminum front end included the hood, hood catch, front fenders, grille filler panel, radiator support panel, fan shroud and front and rear bumpers, as well as their brackets and braces. No radios were installed and most of the Z11s were built without sound deadener or a heater. Don related that Jenkins had told him the inner fender wells were steel in '63, so he swapped them for the aluminum '62 pieces. All totaled, the weight-saving measures reportedly shaved a few hundred pounds from the Impala. A heavier-than-stock battery was installed in the right rear of the trunk to aid in weight transfer.

https://www.hemmings.com/magazine/mus/2014/10/Laudable-Legendary-Lightweights---1963-Z11-427-Impala--1964-426-Race-Hemi-Dodge-330/3742891.html