1967–1969 Chevrolet Impala SS 427: Big-Block Icon

1967–1969 Chevrolet Impala SS 427 — The Big-Block B-Body With Real Bite

Historical Context and Development Background

Chevrolet’s Impala entered the late 1960s at the height of Detroit’s full-size arms race. While the Chevelle SS was capped by GM’s corporate displacement policy for midsize chassis, the full-size B-body had no such restriction. That set the stage for the 427 cu in Turbo-Jet V8 to headline the Impala’s ultimate performance specification: the SS 427.

Introduced for 1967 as RPO Z24, SS 427 bundled Chevrolet’s big-block power with chassis and appearance upgrades. It arrived within the fourth-generation Impala family (1965–1970), during the period when Chevrolet was refining the B-body with improved chassis isolation, coil-spring suspension, and increasingly powerful brake and axle packages. The 1968 lineup gave SS 427 its own identity in the catalog, and for 1969 the package returned to the option column with a revised grille, tail treatment, and the recognizable stripework that enthusiasts often call the “hockey-stick” graphic.

Stylistically, these cars carried the era’s Coke-bottle contours with a domed hood and unique SS 427 badging. The intent was transparent: offer Corvette-grade displacement with dignified space and comfort. In motorsport, Chevrolet’s full-size 427s were no strangers to speed—stock-bodied Chevrolets ran in NHRA’s Super Stock and related categories, while NASCAR calendars of the day featured big-block Impalas. The SS 427’s closest showroom rivals were Ford’s XL/7-Litre and later 428-equipped big Fords, Mercury’s S-55 428, and Chrysler’s 440-powered Plymouth Sport Fury/Dodge Monaco. Pontiac’s 2+2 bowed out after 1967, leaving Chevrolet’s SS 427 to fly the full-size performance flag in significant numbers—albeit as a low-volume halo within the vast Impala range.

Engine and Technical Specifications

The SS 427 centered on Chevrolet’s 427 Turbo-Jet big-block. The L36 was the volume engine; the higher-strung L72—familiar to Corvette and select full-size sleepers—was built in far smaller quantities. Both were iron-block, iron-head OHV designs with forged internals oriented toward sustained high-load cruising and authentic straight-line performance.

Transmissions included the Muncie 4-speed (wide- and close-ratio selections depending on year and axle), a heavy-duty 3-speed manual in limited applications, and the Turbo Hydra-Matic 400—favored for its durability and torque capacity. Posi-traction rear axles were common on SS 427s, with ratios often in the 3.31–3.73 range depending on equipment.

Driving Experience and Handling Dynamics

Driven as intended, an SS 427 delivers huge-wave torque with a long-legged, continental gait. The L36’s single 4-barrel and hydraulic cam profile make for a broad, forgiving powerband, while the L72’s solid-lifter cam, higher compression, and Holley carburetion sharpen the car’s responses and add urgency above 4,000 rpm. Throttle progression is clean and decisive in either tune when correctly set up.

Chassis tuning follows the period’s full-size Chevrolet formula: a perimeter frame, coil springs at all four corners, and a four-link rear. With the F41-type heavy-duty suspension and larger anti-roll bar, body motions are better controlled than the Impala’s boulevard reputation suggests, but ultimately this is a high-speed cruiser rather than a canyon scalpel. Recirculating-ball power steering keeps effort modest—ratio and on-center feel are relaxed compared with contemporary pony cars. The TH400’s crisp, authoritative shifts suit the car’s character; a Muncie-equipped SS 427 feels more urgent but also reveals the sheer mass you’re managing.

Braking started with finned drums; front disc brakes became a valuable option and are strongly preferred today for repeated high-speed stops. Tires of the era were the limiting factor—modern bias-ply reproductions maintain period feel, while radials widen the envelope at the expense of absolute originality.

Performance Specifications

Figures above reflect period-published testing of well-tuned cars and are sensitive to axle ratio, transmission choice, body style, and weather.

Variants and Year-by-Year Notes

Across its three-year run, SS 427 evolved from an option to a unique identity and back again. The following snapshot summarizes the key differences enthusiasts and collectors track, along with widely-cited production totals.

Notes: Totals are widely cited by marque historians and reflect the SS 427 configuration overall, not engine-code splits. Documented L72 SS 427s exist but are a minute fraction of production.

Ownership Notes: What to Know Before You Buy

• Drivetrain robustness: The 427 big-block, Muncie 4-speeds, 12-bolt rears, and TH400 automatics are famously durable when maintained. Expect heat soak and fuel-percolation sensitivity if under-hood insulation, carb spacers, and heat shields are missing.
• Valve lash: L72’s solid-lifter cam requires periodic lash checks; owners often set and verify at oil-change intervals.
• Cooling and fuel: Both 427s expect high-octane fuel and a sound cooling system (heavy-duty radiator, correct fan clutch/shroud). Overheating complaints usually trace to timing, vacuum advance, or incorrect pulleys/shrouding.
• Brakes: Front discs transform confidence and are a sensible upgrade if the car retains drums. Original-style parts are available; ensure the proportioning valve and booster are correctly matched.
• Rust and structure: Common zones include trunk floors, rear quarters, lower fenders, cowl and windshield base, body mounts, and the perimeter frame rails. Convertibles used additional frame boxing; inspect carefully for corrosion and alignment.
• Trim scarcity: Z24-specific pieces (domed hood, emblems, moldings, stripe layouts, gauge packages) are harder to source than mechanical parts. Nice original or quality NOS/replica items carry premiums.
• Parts availability: Big-block service parts, ignition, cooling, and brake components are straightforward; interior soft trim and some brightwork require patience.
• Documentation: A genuine SS 427 should present matching VIN/body tags, build sheets (if found), and correct engine/trans stampings. Casting dates and suffix codes should align with build dates.

Cultural Relevance and Market Standing

The SS 427 occupies a respected niche: a full-size Chevrolet with Corvette displacement and credible straight-line performance. While the Impala nameplate is a fixture in film and television, the specific SS 427 variant remains an insider’s choice—recognized at shows and highly regarded among full-size Chevrolet devotees. Period drag racing cemented the platform’s capability, and NASCAR put 427-powered Chevrolets in front of grandstand crowds.

Collector interest follows specification and provenance. Well-documented L36 cars in excellent condition routinely outpace equivalent small-block SS Impalas, while authentic, correctly restored L72 cars occupy the top rung and have crossed into six-figure territory at major auctions when condition, correctness, and documentation align. Factory 4-speed cars, original paint/trim colors, and rare body styles add meaningful premiums.

Frequently Asked Questions

How can I tell a true SS 427?
Look for proper Z24 indicators for the year: domed hood and SS 427 badging, heavy-duty cooling and suspension components, correct gauge packages, and documentation. Engine and transmission stampings should match suffix codes and dates consistent with the body tag. Be wary of clone builds; the cosmetic bits can be added, but factory paperwork is decisive.

What’s the difference between L36 and L72?
L36 uses a hydraulic-cam 427 with a single 4-bbl (Quadrajet) and 10.25:1 compression rated at 385 hp (SAE gross). L72 adds a solid-lifter cam, 11.0:1 compression, and a Holley 4-bbl for a factory rating of 425 hp (SAE gross). L72 cars are notably rarer and more temperamental in tuning, but faster when set up correctly.

Were front disc brakes standard?
No. Drums were standard, with power front discs optional and strongly recommended for spirited use. Many surviving cars have been retrofitted with factory-spec disc hardware.

What axle ratios were available, and how do they affect performance?
Common SS 427 ratios ranged from around 3.31 to 3.73 with Posi-traction. Shorter gearing (3.55–3.73) quickens acceleration at the expense of relaxed highway rpm; taller gearing favors long-distance cruising and quieter cabin speeds.

How does the SS 427 compare to period competitors?
Against Ford’s XL/428 and Chrysler’s 440-powered big coupes, the SS 427 delivers comparable or better straight-line speed with Chevrolet’s parts-bin depth and serviceability. The Impala’s ride quality and refinement are strengths; handling is secure rather than sharp, reflecting full-size priorities.

What are common problem areas?
Cooling inefficiency from incorrect shrouds/pulleys, fuel boil-over in hot restarts, worn front-end bushings and idler arms, leaky heater cores, and corrosion in the usual GM B-body spots. Big-block exhaust manifolds can crack from heat cycles; verify casting integrity.

Are these engines the same as Corvette units?
They share core architecture and many internal specifications. Accessory drives, carburetion, and calibration differ by application. The L72’s character is similar across platforms but installation details (exhaust, pulleys, brackets) are model-specific.

What’s the service rhythm for an L72 car?
In addition to routine oil and ignition service, plan periodic valve-lash checks, careful ignition timing and advance curve setup, and attention to fuel quality. These steps keep the solid-lifter 427 crisp, cool, and happy.

Why the SS 427 Still Matters

The SS 427 distilled Chevrolet’s big-block ethos into a package that could haul five adults and annihilate a quarter-mile in authentic, understressed fashion. As a bridge between luxury and muscle—backed by a deep bench of parts and knowledge—it remains one of the most usable and rewarding blue-chip full-size performance cars of its era.