Table of Contents
How Did The Chevy 409 Engine Come About?
The story of the 409 began about three years earlier with the development of the first W-Series engines in 1958. The Mark I was a cast iron block overhead valve design with offset valves Chevy developed for its full line of passenger cars and trucks. The original 348 ci (5.7L) V8 was designed to fit into the same space as the current small block V8s GM had used but produced more power. The Mark I accomplished this with its combustion-in-chamber design.
With a unique piston head design that looked more like a gabled roof or wedge than a flat cylinder head, the spark plug was mounted dead center so that as the piston reached the top of its arc, there was a smaller area for the combustion in the chamber. The smaller wedge-shaped chamber provided a significant improvement in power. The initial 348 made 250 hp and 355 lb/ft of torque. GM marketed the engine as its “Turbo-Thrust” V8 (or Special Turbo Thrust, depending on the carburetors - a single 4 bbl or a triple 2 bbl configuration).
Over the years of its production, the engineers kept pushing the power output up bit by bit until in its last year (1961), the high-output 348 version (labeled as Special Turbo Thrust was producing 340 hp for the four bbl carb, and 348 hp for the 3 x 2 bbl carb versions which had the moniker of Super Special Turbo Thrust). Ford’s success with their beefed-up 390 V8s forced GM to scrap the 348 as their primary production engine in 1961 for passenger cars, although the 348 V8 continued to be used as a truck engine until 1964.
What Were The Features of the Chevy 409?
Desperate to compete, GM increased the displacement of the W-Series engine by equipping larger ports and valves and increasing the bore and stroke to 4.31 X 3.5 inches. The result was that the engine displacement increased to 6.7 L along with a sizeable bump in the compression ratio from 9.5:1 to 11.25:1. The increase in power didn’t go unnoticed, and GM offered the new 409 V8 engine in the launch of their new Impala SS (Super Sport) in the latter half of 1961. The initial engine was paired with a single four-barrel carburetor.
In 1962, the engine was tweaked to 380 hp with a particular version of the 409 married to dual-quad aluminum intake manifolds and two four-barrel Carter AFB carbs. The Beach Boys sang about this unique dual quad version of the 409 when the second verse proclaimed the merits of the four-speed dual quad 409. Unfortunately, the song didn’t do much more than crack the Billboard Top 100, landing at 76 for a week before falling like a stone.
By the time 1963 rolled around, the 409 V8 Impala was making a name for itself on the drag strips. The peppy little engine produced 425 hp and 455 lb/ft of torque, with 0-60 speeds in 7.5 seconds (although many owners were getting much better times). With the Chevrolet Impala SS hitting close to 150 mph as its top speed, it was significantly faster than its Ford Galaxie counterpart, which had a top speed of 135 mph.
When NASCAR champions Rex White and Ned Jarrett began racking up wins with the 409 V8 engines in ‘61 and ‘62, consumers realized that there was something special about the Impala SS and its Mark I powerplant.
By the time of the Daytona in 1963, GM unveiled a unique 409 “mystery engine” (a 427 cubic inch 7.0L motor that was based on the 409). This remarkable engine was designed specifically for drag racing and NASCAR with reinforced cylinder walls, forged steel crankshafts, and a two-piece aluminum intake manifold.
With an increased bore and stroke, the compression jumped to 13.5:1, and the power output went to 430 hp and 575 lb/ft of torque. When Junior Johnson stomped the competition in the first 100-mile qualifying race, and Johnny Rutherford blistered the second 100-mile race, the racing world took notice. Though Chevrolets won both qualifying races, they failed to win the Daytona due to mechanical issues (although Rutherford finished ninth, behind a whole line of Ford Galaxie 500s). The engines made enough of an impression that competitors paid attention to the new configurations and were sent back to their garages, trying to duplicate the 427 mystery Mark II effort.
What Are The Specs of the Chevy 409 Engine?
Eventually, the 409 was superseded by the 396 V8 that GM instituted in the fall of 1965 for the following model year. The Mark IV engine was a complete departure away from the former chamber-in-block design of the early W-Series engines. The new engine is attached to a 90-degree block deck. The valves were placed to open away from the combustion chamber and cylinder walls. While the base of the new engine was still cast iron, the walls were thicker to handle heavier loads. The Mark IV first appeared in the 1965 Corvette and became the 7.0L 427 workhorses that found its way in several full-sized Chevy models in the late sixties.
Why Did The 409 Get Such A Bad Rap?
Even though the 409 was blowing away the competition on the Nascar ovals, GM soon discovered that the engine had severe issues.
Overheating
The early big blocks tended to overheat and seize up when pushed to the limits (as often happens in racing situations). Even though the Mark I had a side-mounted oil cooling system, it was inadequate. With the same size radiator and water pump as the 348, the components were too small to handle the excessive strain of high rpms. As the engines overheated, they tended to become quite noisy (excessive knocking), which didn’t endear them to customers.
Thin Cylinder Walls
Because the 409 was a bored-out 348 (and the racing 427 mystery engine was a bored-out 409), so the cylinder walls were too thin to handle the stress of continued rpms. Many Impala owners suffered from cracked blocks or dropped valves. Of course, once these kinds of problems happened, about all a young person could do was park their Impala in the garage until they could save up for another engine.
Heavy Oil Consumption
The issues with overheating contributed to all kinds of gasket and seal problems, and the 409 was notorious for guzzling oil. The W-engine (Mark I - 348) was initially designed as a truck engine. The motors performed adequately as long as they were pushed hard, which made them ideal daily drivers.
