Big Block (Rat) Chevy

Unlike smaller engines, the big-block Chevy’s evolution can be traced back to a high-performance 425-hp L78 396, originally offered in 1965 Corvettes and Chevelles. Although the big-block was destined for trucks and family sedans, it began as a serious high-performance item with rectangular port heads, a solid lifter cam, a high-rise aluminum intake manifold and a 780-cfm Holley carb.

To make matters worse, advertising and marketing methods were twisted to boost sales. For example, the identical L78 396 engine produced 425 hp in a Corvette but only 375 hp in a Camaro or Chevelle. In addition to improved exhaust manifolds and a free-flowing air cleaner, the Corvette engine’s 6,400 rpm rating distinguished it from the Camaro and Chevelle engines’ 5,600 rpm ratings. Not actually “lying,” but reporting horsepower ratings below the true peak power level to avoid competing with the famed Corvette.

There are thousands of hours of research and development that went into this modern 500-ci Pro Stock engine. Every system has been massaged, flowing, tested, and altered to maximize drag strip performance. A constructed sheet-metal tunnel-ram intake manifold houses two 4500 series carbs;  stainless steel headers with merge collectors; a crank trigger ignition system; a belt-driven camshaft and front-drive distributor; and a dry sump oil pump and pan with a full-length kick out. One-inch lift titanium valves push on enlarged keyway-guided roller lifters, a bespoke nine-bearing roller camshaft and a GM DRCE iron block with compacted graphite and 4.900-inch bore spacing. With a compression ratio of over 15:1, high-ratio shaft-mount rocker arms provide valve train stability. The cylinder heads are NHRA-legal GM DRCE castings that are fully CNC machined to each team’s specifications.  

In 1972, insurance companies started charging more for high-performance cars. Chevrolet used the more realistic net horsepower number, which reflected the true “as delivered” output of the engines with all accessories and a stock exhaust system. Because the GMPP crate engines were never used in production vehicles, their horsepower numbers reflect their total output.


325 BHP

Holley 4-barrel carb till 1967, Quadrajet 4-barrel after 1967, 10.25:1 compression, two-bolt main caps, and forged steel crankshaft. Until 1972, most full-size automobiles, Camaros, and Novas had it.


Improved hydraulic lifter cam, open-element air cleaner, dual exhausts. Mains bolted to forged steel crankshafts. With Holley 4-barrel carb until 1967, then Quadrajet 4-barrel starting in 1968. From 1966 through 1970 in Chevelles and Camaros.  The L34 396 had a factory-rated 25-hp improvement over the L35 396 thanks to an open-element air filter, higher lift hydraulic cam, and dual exhaust.

425 BHP

A forged steel crankshaft and rectangular port cast iron heads with an 11:1 compression ratio. It was offered through 1970 in Corvettes and Camaros. An open-element air cleaner and high-flow exhaust manifolds were included. Above the oil filter boss, the block was tapped for the oil cooler, as was common in the muscle car period. Some had Closed chamber rectangular port aluminum heads, high-rise aluminum intake manifold, 780-cfm Holley carburetor, forged pistons with 11:1 compression, four-bolt main caps, and forged steel crankshaft.

375 BHP

Intake manifold: high-rise aluminum with 780 cfm Holley carburetor; pistons: forged pistons with 11:1 compression ratio, four-bolt main caps, and forged steel crankshaft. Z-16 Chevelles.



In 1970, only the 402 had 10.25:1 compression ratio (down to 8.5:1 in 1971 and later) and two-bolt main caps. Mostly in Camaros and Chevelles. The 1972 SAE engine test protocols resulted in reduced horsepower ratings.  This engine has a 4.125 inch bore, oval port cast iron heads, higher lift hydraulic lifter cam, Quadrajet 4-barrel carb, 10.25:1 compression ratio and dual exhausts. Most had two-bolt main caps, although others had four-bolt blocks.

375 BHP

Engine features wider bore rectangular port cast-iron heads, high-lift solid lifter camshaft, high rise aluminum intake manifold, Holley carburetor (780cfm), four-bolt main caps and a forged steel crankshaft.


There were two-bolt main caps and an oval port cast-iron head on this engine.  Only in 1969 mid size automobiles.   Also the 427 engine with bigger bore higher-lift hydraulic lifter cam, Quadrajet 4-barrel carb, 10.25:1 compression ratio, and dual exhausts. It was only fitted on Corvettes.

400 BHP

The L36 427 engine has oval port cast-iron heads, a higher-lift hydraulic lifter cam, 10.25:1 compression ratio, and dual exhausts. Only 1967–1969 Corvettes. A forged steel crankshaft and three 2-barrel carburetors with open-element triangle air cleaners.

425 BHP

The L71 427 engine has rectangular port cast-iron heads, a high-lift solid lifter cam, forged pistons with an 11:1 compression ratio, four-bolt main caps, and a forged steel crankshaft. It produced 450 horsepower in Corvettes, in other cars 425 hp.

Three 2-barrel carburetors, open-element triangular air cleaner, high-lift solid lifter cam, forged pistons with an 11:1 compression ratio, four-bolt main caps, and forged steel crankshaft.

430 BHP

This famous engine ruled the iron-block 427s. There were aluminum rectangular port heads with closed chambers from 1967 to 1968, and open-chamber heads from 1969. 7/16-inch pushrods, 12.5:1 forged aluminum pistons; four-bolt mains, forged steel crankshaft The L88’s conservative hp rating was significantly below its genuine peak power. With tubular exhaust headers, they could create 550 horsepower at 6,400 rpm! 1967-1969 solely in Corvettes.

This unique all-aluminum L88 engine is the crown gem of the muscle car era. Only two Corvettes and 69 Camaros were sold in 1969. 7/16 inch pushrods, 12.5:1 forged aluminum pistons, 4 bolt mains and a forged steel crankshaft were among the features.


2-bolt main caps, oval port cast iron heads, Quadrajet 4-barrel carb, mild hydraulic lifter cam it was the last big-block offered in Corvettes in 1974. In 1970, the LS5 produced 390 gross horsepower in Corvettes, 360 gross horsepower in Chevelles and Monte Carlos, 365 gross and 285 net horsepower in 1971, and 271 net horsepower in 1972 and later.

Dual exhaust, Oval port cast iron heads, Quadrajet 4-barrel carb, low restriction air cleaner, high-lift hydraulic lifter cam, 8.5:1 compression. Larger automobiles like Corvettes featured free-flowing exhaust manifolds.

425 -450-460 BHP

A rectangular port head with closed chambers in 1970 (11:1) and open chamber heads in 1971 (11:1 compression ratio) (9:1 compression). Equipped with forged aluminum pistons, four-bolt mains, and a forged steel crankshaft.

465 BHP

However, it is said that some of these bad boys made it into production cars. With an aluminum high-rise intake manifold and Holley 830-cfm carb, aluminum rectangular port heads with open chambers, a custom “off-road” solid lifter cam, 7/16-inch pushrods and a 5140 forged steel crankshaft, it was a boosted L88.