Does history really repeat itself?

Does history really repeat itself?

How the LS design was inspired by the “W” motor of the late ‘50s/early ‘60s...

To understand why GM’s supercharged LSA motor is the performance piece that it is, one must first understand how the evolution and performance of the LS series as a whole is indirectly connected to Chevy’s first ever production big block, the “W” motor first introduced by Chev in 1958 as part of their large-truck/full-size passenger line-up.

Actually, the original 348 big block, Chevy’s notorious W-shaped motor, was as much of a mechanical/technological milestone as the LS series that was introduced by GM in 1997. In terms of valvetrain construction, the “W” motor was a motor ahead of its time, using parts and techniques that were pretty non-conventional by ‘50s/early ‘60s standards. These included an overhead cam, with pushrods that were used as reservoirs for the motor’s overall oiling system. The “W” motor shared in common with the 265 and 283 small blocks a valvetrain consisting of tubular steel pushrods tapping stud-mounted, stamped steel rockers, an innovative design which allowed Chevy’s 348 to rev well-past 6,000 RPM, a considerably high range for a big block. This rocker arm assembly also allowed Chevy to build future big block V8s with an inclined-valve design, a layout that would force the engine’s valves to open away from the combustion chambers and cylinder walls.

But where the true meat of 348, and later 409, performance lies is in the head and piston designs, which much later on would become true of the LS engine family. For example, Chevy’s W mill incorporated crowned pistons with a head deck design that deviated from the traditional perpendicular design.

The 348/409 series also deviated from the standard chamber-in-head design, placing the combustion chambers in the block instead. The idea behind this and the vertical spark plug layout that accompanied the non-conventional combustion chambers was that a more turbulent flame front could be produced within the chambers by forming a “wedge” shape between the piston crown and the chamber itself. In other words, instead of using flat-topped pistons, Chevy used piston “crowns” to compress the air/fuel mixture tighter, which would naturally make for a more turbulent engine-running dynamic. It was the flat-torque characteristics of the W motor that made it successful in large trucks and full-size passenger cars.

This “flat-torque” dynamic was also achieved by the 348’s offset valve layout, which would ultimately become the Chevy big block hallmark. The reason that this was true is that Chevy intended the offset valvetrain to build maximum brake mean effective pressure at relatively low-running speeds, which was how the motor built bottom-end torque.

Once Chevy would introduce what they called the “Mark IV” generation of big blocks, including the 396, 427 and 454 motors, not much would change from the 348/409 series, except that the Mark IV motors would eventually turn out to be substantially souped-up versions of the original “W” motor. In fact, the second generation of Chev big blocks maintained the offset valves, but where the new big blocks differed from the originals was in the return to an in-head chamber instead of those cast into the cylinders. The Mark IV big blocks also returned to the 90-degree, cylinder head-deck design, and with this and the new inclined valve layout, the unmistakeable W-shaped valve covers of the 348 motor were no longer needed, which meant Chevy could return to traditional, square valve covers on their big block series. The inclined valves were also accompanied by spark plugs that entered the combustion chambers at an angle instead of vertically; this new spark-to-valve combination made for even furthered performance at yet higher RPM ranges.

With the introduction of the LS engine series, not much changed in terms of the concepts of effective mean pressure and overall volumetric efficiency, except that the LS has a dry weight of somewhere in the 400-pound range, where the Mark IV big blocks had a dry weight of around 685 pounds, with the all-aluminum, ZL1 427 being the exception.

 Come to think of it, the LS engine, especially with the introduction of the Generation IV series in 2005, was and still is a computer-controlled version of the “W” motor. Both the LS and the original big block engines were head-and-valvetrain deviants; where the 348/409 series deviated from the 90-degree deck design of the conventional small block, the LS series likewise deviated from the conventional small block’s pentagonal, five-bolt head pattern, abandoning this for an oversquared, four-bolt design.

Like the W motor, the LS is also a deviant in terms of spark; where the W motor, for years, had used vertically-inserted spark plugs, it eventually abandoned the layout for one using angled plugs in order to improve combustion, and the LS series would abandon distributors all-together, introducing a relay-pack system known as coil-near-plug ignition.

Both the 348 and LS series introduced to the GM market new ways of designing/building bottom ends; with the introduction of the 348 big block, GM incorporated a then-new piston profile which included a “crown” for increased compression and flame front turbulence, while the LS family introduced the use of hypereutectic pistons and the 1-8-7-2-6-5-4-3 firing order, a cylinder firing-order that was more in-line with Ford’s modular and other late-model V8s that would be the LS’ contemporaries.

In almost every industry and every facet of life, it’s been said that history repeats itself; in the world of engine performance, the compare-and-contrast between the 348 and the LS motor stands as brilliant evidence of this idea.

- Sal Alaimo Jr., B. A. (7/26/11)

S. J. A.