Chevelle Engines Guide: Sixes, Small Blocks, 396, 402 and 454

Over its fourteen model years the Chevelle was offered with a remarkable range of engines, from economical inline sixes to some of the most powerful engines Detroit ever put in an intermediate car. This guide covers the main engine families, explains where each one fits, and gives an honest account of the horsepower ratings, which mean different things depending on the year.

First, a word on gross versus net ratings

Until 1971, American manufacturers advertised SAE gross horsepower. Gross figures were measured on an engine running without the full production accessories, intake and exhaust restrictions that it would carry in the car. For 1971 Chevrolet published both gross and SAE net figures, and from 1972 it quoted net figures only. Net ratings measure the engine much closer to how it is installed, so they are substantially lower for the same hardware.

Two more complications are worth knowing:

• Advertised ratings in the muscle era were also shaped by marketing, insurance and corporate policy. Some engines are widely believed to have been rated conservatively, and others optimistically.
• For 1971 GM lowered compression ratios so engines could run on lower-octane fuel, so 1971 and later engines did lose real power, not just paper horsepower.

The upshot: comparing a 1970 gross figure with a 1972 net figure tells you very little. Compare like with like, and treat all period ratings as approximate.

Inline six-cylinders

Large numbers of Chevelles left the factory with Chevrolet's inline sixes, including the 194, 230 and 250 cubic-inch versions depending on the year. They are durable, simple and easy to maintain. Six-cylinder cars are common donors for SS clones, which is one reason a car's original engine type matters when you assess its history.

Small-block V8s: 283, 327, 307, 350 and later

The small-block Chevrolet V8 powered most V8 Chevelles.

• 283: the original Chevelle V8 in 1964, offered in two- and four-barrel versions through the first generation.
• 327: added during the 1964 model year and offered in several states of tune through the late 1960s, including high-performance versions. A strong 327 Chevelle was a quick car in its day.
• 307: introduced for 1968 as the base V8, replacing the 283, and used into the Colonnade years.
• 350: offered in the Chevelle from 1969. From 1971 the SS package could be ordered with a 350, which is why a 1971–72 SS does not necessarily have a big block.
• Later small blocks: Colonnade cars used the 350 and other small blocks, with the 305 appearing late in the run, all in emissions-era tune.

Small blocks are lighter than big blocks, which helps handling, and parts for them are among the cheapest and most plentiful in the hobby.

The 396 big block

The 396 cubic-inch "Mark IV" big block made its Chevelle debut in the 1965 Z16, rated at 375 hp. From 1966 through 1969 it powered the SS 396, which is why that era is remembered as the time when "SS" on a Chevelle meant a big block.

The 396 was sold in several versions. Commonly cited Chevelle ratings are 325 hp (L35), 350 hp (L34) and 375 hp (L78), the last being a high-compression, solid-lifter engine aimed at serious performance. For 1969 an aluminum-head version of the L78, the L89, was a rare and expensive option. Exact availability varied by year, so check year-specific references before assuming a given version was offered.

The 402, wearing 396 badges

For 1970 Chevrolet enlarged the 396 by increasing its bore, giving 402 cubic inches. The Chevelle kept its SS 396 badges anyway, so a 1970 "396" is actually a 402. Chevrolet later marketed the engine under the Turbo-Jet 400 name. Its ratings fell sharply in 1971 and 1972 as compression came down and net figures took over.

The 454: LS5 and LS6

When GM dropped its internal limit on engine size in intermediates for 1970, Chevrolet installed the 454 in the Chevelle SS 454.

• LS5: the hydraulic-lifter 454, rated at 360 hp gross in 1970. It continued into 1971 and 1972 with lower compression and lower ratings, quoted as both gross and net in 1971 and net only in 1972.
• LS6: the high-compression, solid-lifter 454 rated at 450 hp gross, available in the Chevelle for 1970 only. It is the highest factory rating of the classic muscle car era. See our dedicated 1970 SS 454 LS6 article.

The 454 also appeared in early Colonnade Chevelles, but in emissions-era form with far more modest net ratings.

Quick-reference table

Years in this table are approximate. Offerings changed mid-year and by market (for example California emissions versions), and sources differ on some details.

Transmissions and rear axles

Automatic choices included the two-speed Powerglide and, in later years, the three-speed Turbo Hydra-Matic in its 350 and 400 versions, with the stronger 400 generally paired with big blocks. Manual choices included three-speed and four-speed gearboxes, with the Muncie four-speed in wide-ratio, close-ratio and heavy-duty close-ratio versions popular on performance models.

Rear axles were typically 10-bolt or 12-bolt designs, with the 12-bolt common behind big blocks. Axle and transmission codes are part of the evidence experts use when evaluating a car; see how to identify a real Chevelle SS.

Choosing an engine today

If originality matters, keep or restore the engine the car was built with; a correct, original engine is a large part of a collector Chevelle's value. If you want a driver, a healthy small block is cheaper to run and easier on the front suspension, and a modern crate engine can add reliability and power. Whatever you choose, document what is in the car and keep the original block if you replace it.