The New Engine Meant A New Direction
While GM had plenty of experience with Big Blocks (the first Mark 1 debuted in 1958), the Mark IV represented a new direction in engine design. The old W-series (1958) was a big-block Chevy engine with a chamber-in-block design (cast iron heads and block). While it was great for low-end torque, it tended to lose power during high-rpm performance. While it was perfect as a truck engine (or for a heavy-duty passenger car), GM knew that the public demanded faster cars requiring more powerful big block engines.
Chevy scrapped the heavy cast iron design in favor of a more conventional 90-degree wedge-shaped deck. The valve placement was repositioned to an angled position, opening away from the combustion chamber, lessening the impact on the cylinder walls. Aggressively closed chamber heads improved combustion and assisted with the high rpm operation. The spark plugs were installed at an angle rather than straight down. The intake and exhaust system was enhanced, and the larger exhaust valve size was a staple of the production engine.
Many 427s were equipped with aluminum intakes, with more aggressive hydraulic roller camshaft as had been a part of the W-series. The innovations resulted in much-improved performance with better compression ratios, which made the engine ideal for both large vehicles on the street and the track.
The designers knew that the higher power output would require a beefed-up cylinder block, forcing Chevy to reinforce the cast iron version they’d been using. Chevy used several mechanical components from the W-series, including the side oil lubrication system, which assured maximum oil flow to the aluminum rod bearings.
How Many Variations Of The 427 Were There?
GM’s “Turbo-jet” engines were offered as extra-cost options in full-sized Biscayne, Impala, Caprice sedans, station wagons, and Corvettes. The 427s came out in two versions with the same bore and stroke, 4.25 x 3.76, and were initially offered for the 1966 - 69 model year.
The Baby 427 (L36)
Chevy offered both “Turbo-jet” engines to bolster its sales and appease younger buyers who were demanding better performance from their vehicles. The smaller L36 7.0 L V8 produced the most negligible power output (390 hp) and had the lowest compression ratio of 10.25:1. The engine was equipped with two bolts holding the main caps, had hydraulic lifters, with a standard Quadrajet four bbl carburetor and dual exhaust.
The Hefty L72 V8
The most effective option for owners who wanted speed and power was the 425 hp version 7.0L 427. It was Chevy's most significant engine in 1966 (except for some specially designed L88 V8s). The L72 found its way into the full-sized line and Corvette as an alternative to the less powerful V8 motors Chevy had been using. To boost power for the big block, Chevy raised the compression to 11.0:1. It also strengthened the main cap bolts to four and provided an enlarged Holley 4bbl carb to provide a better fuel/air mix. Enhanced crankshaft journals and bearings provided more rigidity and increased endurance at higher rpms. Chevy had to compensate for the 425 hp by offering an increased aluminum intake and exhaust manifolds.
The L72 began to gain popularity as it entered the Corvette. It blazed down the track at 0 - 60 mph in 4.9 seconds (11.9 second quarter mile time). Coupled with the 140 mph top speed, Corvette sales began to take off, up over the previous year by almost 16%.
The L72 did appear in several full-sized models in 1966. The Caprice, Biscayne, Bel-Air, and Impala models. (Only 1,826 engines made it into these models in 1966). Unfortunately, Chevy tinkered with the L72, offering an upgraded version, the L71, with 435 hp). Only 12 known L72s made it into production in 1967 across the entire lineup, as Chevy reversed its decision, bringing the powerful L72 back into the mainstream.
In 1969, Chevy did make a few mid-sized Chevelles and base Camaros with the L72 engine. Customers could specifically request a Central Office Production Order, which bypassed an internal company rule limiting the horsepower of a V8 to under 400 hp in vehicles other than full-sized cars or Corvettes. Many collectors search high and low for a COPO car since only 69 Camaros and 300 Chevelles were built with the specially ordered engine.
The 427 Gets Tweaked, But Not For the Better
In 1967, Chevy offered three 427s to the public, the L36 (390 hp), a modified version (L68) which produced 400 hp, and took the L72 to 435 hp (which got the moniker of L71). The new engines (L68 and L71) received a three-two-barrel carburetor setup. (other than the change in carburetors, the two engines are identical in every way). The increase in fuel/air mix pushed the horsepower up but did not move the Corvette faster down the track. The public wasn’t that impressed with the move, and Corvette sales saw a dip down to 22,940 units. The loss wiped out almost all the gains they had made the previous year. GM brought back the L72 for the ‘68 model year for full-sized models, but not the Corvette. Instead, the company kept firm with the three 427s (L36, L68, and L71). With the inclusion of two small block V8s, the 300 hp, and 350 hp, customers had plenty of options. The tactic worked as Corvette sales for ‘68 and ‘69 spiked once again. (Over 39k were sold in ‘69).
The L88 Is Collector’s Item
Of all the variants of the 427, the L88 is the most powerful motor Chevy built in the late 60s.
It was primarily built for 218 Corvettes between 1966 - 69 and could be specially ordered as a Stingray or Coupe model. (GM built most of the L88 for racing applications, never intending for the car to be made for street use, but it did happen).
GM tried to “fudge” the new engine's power to keep the public from rushing to get the increased engine. (Everyone wanted to go faster). Officially, they rated the new engine at 430 hp, similar to the L71, but most Corvette owners found the power output much higher - some pushing over 550 - 575 hp. Word began to get out, and customers who could afford the price (the L88 model was almost double the price of a standard Corvette) were rewarded with a barely street-legal Corvette with a top speed of 175 mph.
The L88 featured a cast iron block with all aluminum heads, a more solid lifter cam designed for racing, and a massive 850 CFM dual feed Holley Carb with a cold induction system. Producing a 12.5:1 compression, the Corvette was fast, which was soon proved on the racetrack. The first 1967 L88 prototype was given to Roger Penske, whose team of drivers won the 1967 Sebring 12-hour endurance race and then finished 2nd in the ‘67 Daytona. (It would go on to win the following year).
The 1967 version of the L88 was illegal to drive on the street due to a non-legal crankcase vent system, but changes were made for the ‘68 and ‘69 models that helped make these rare Corvettes legal much to buyers' delight.
The ZL-1 Racing Motor
The ZL-1 motor was available in late racing applications for Corvettes, Camaros, and other vehicles. The racing ZL-1 had an aluminum block and aluminum cylinder heads, which improved the weight of the motor (only 575 lbs), which made it perfect for the track. Many collectors search for these rare ZL-1 motors, although they are available as a crate engines.