The Z11 Impala was a 1963 Chevrolet built for the drag strip and almost nothing else. It carried a special 427-cubic-inch V8 rated at 430 horsepower and a front end made largely of aluminum. Chevrolet built fewer than 60, and only a handful survive. The goal was simple: beat Ford, Pontiac and Chrysler at the track.
On paper, it looked like a full-size family car. Underneath, however, it was a racing package sold through the order form.
What follows covers what went into a Z11 Impala, what it cost and how few are left.
A 409 stretched into a 427
First, the engine started as Chevrolet’s 409. According to the Chevrolet 348/409 reference site 348-409.com, the Z11 427 kept the 409’s 4.3125-inch bore and used a longer 3.65-inch stroke. It also got special heads, valves and a new intake manifold.
That site lists the rating at 430 hp at 6,000 rpm, on 13.5:1 compression. Meanwhile, two Carter AFB four-barrel carburetors fed the engine. Real output, the site adds, ran higher than the rating. Conceptcarz gives the same 430 hp and about 575 lb-ft of torque, and it notes the stroke added 18 cubic inches over the 409.
The parts list reads like a race engine’s. 348-409.com lists heads with 2.19-inch intake and 1.72-inch exhaust valves, plus a camshaft with .556 inches of lift and 325 degrees of duration. The intake manifold came in two pieces. Finally, an aluminum water pump rounded out the package, while the tachometer redlined at 6,200 rpm.
The 427 breathed in a new way too. Chevy Hardcore describes a special air cleaner that sealed to the firewall with a rubber boot and pulled air from the cowl. In fact, it calls that cowl induction a first for Chevrolet.
How the Z11 Impala lost 300 pounds
Weight, however, was the other half of the Z11 Impala formula. 348-409.com lists the aluminum parts: hood, fenders, front and rear bumpers, bumper brackets and braces, grille brackets, a two-piece fan shroud, a grille filler panel and the hood support catch. Together with other deletions, that made the car about 300 lb lighter than a comparable 409 Impala.
Chevrolet also stripped out comfort items. Chevy Hardcore says the radio, front sway bar, sound deadener and heater came out. In their place went a deep-sump oil pan, sintered metallic brakes, a Borg-Warner T-10 four-speed and a Positraction rear axle with 4.11 gears.
The chassis got its own pieces as well. 348-409.com notes rear brake backing plates with screens and air scoops for cooling. Even the wheels were specific, since the Z11 rolled on 15 x 5.5-inch wheels with 6.70 x 15 bias-ply tires.
Even so, it was not a featherweight. 348-409.com lists a shipping weight of 3,245 lb and a curb weight of 3,405 lb.
The Z11 also had a forerunner. According to 348-409.com, Chevrolet built about 20 special-order 1962 Impalas late in that model year with aluminum front ends. In addition, those cars ran 409s with Z11-style heads, intake and camshaft.
What a Z11 cost in 1963
Still, the option was not cheap. 348-409.com lists the base 1963 Impala at $2,774 and the Z11 package at $1,240. That brought the total to just over $4,000 before destination charges and taxes. Conceptcarz gives a slightly different option price of $1,245.
In other words, a buyer paid close to half the price of the car again for the package. Yet not every buyer was a racer. 348-409.com says some Z11s sat on ordinary dealer lots.
How many Chevrolet built
The exact count remains debated. 348-409.com says Chevrolet built 57, all for 1963, the only year of the option. Conceptcarz says about 50 left the Flint plant, possibly as many as 57.
Conceptcarz also gives the shipping dates. Twenty-five cars left the factory on December 1, 1962, and another 25 followed on January 1, 1963. Later, it believes, about seven more followed. Meanwhile, Chevy Hardcore settles on fewer than 60, with most estimates between 50 and 57.
On the strip, then gone
Meanwhile, the cars went racing. Chevy Hardcore says Ronnie Sox of Sox & Martin owned and raced his own Z11, which regularly ran low 11.20-second elapsed times. The site also pictures a Z11 owned by Jack May, driven by Larry Wilson and prepared by Sox.
The program did not last. According to Chevy Hardcore, GM’s corporate racing ban in 1963 ended development of the 427. As a result, racers moved to other makes, and factory support dried up.
As a result, few cars made it through. Both 348-409.com and Chevy Hardcore put the number of surviving Z11 Impalas at about seven.
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