PH Origins: Cylinder deactivation


Mention cylinder deactivation to an enthusiast and Cadillac's early V8-6-4 system will no doubt make its way into the conversation at some point. Justifiably so, given that the company's venture into the land of 'displacement on demand' resulted in the first mass-produced and automatic system of its kind.

The justification for such a complicated system was easy to understand, as was the concept of the technology itself. In the early 1980s, following the oil crisis, American manufacturers were battling to meet the increasing regulatory and public demand for more efficient engines.

Cadillac, for example, had been downsizing both its cars and its engines in an effort to meet the new requirements; in 1977, it had introduced a carburetted 7.0-litre V8 dubbed the L33. It produced - brace yourselves - an underwhelming 180hp and 320lb ft, in part due to the company's efforts to meet stringent emissions regulations with the technology available at the time.

A version with electronic fuel injection followed, called the L35, which produced a similarly unremarkable 195hp and 320lb ft. In 1978, however, the 'Corporate Average Fuel Economy' regulations had been introduced. These laid down fuel economy targets for manufacturers, in an effort to boost vehicle efficiency.

The L33 and L35 V8s were not capable of meeting the new targets, so Cadillac rolled out a downsized powerplant - the 6.0-litre L61. Output predictably sagged, compared to past efforts, with the company eking just 145hp and 270lb ft out of its low-compression V8.

It was not, unsurprisingly, as efficient as Cadillac hoped it would be - both with regards to fuel consumption and emissions - and the company was, for one thing, going to struggle to meet the next round of CAFE targets.


A new approach was required, as continuing to reduce the engine's displacement wasn't having the desired effect. The ever-shrinking power and torque figures would ultimately lead to dissatisfied customers, too, particularly given that there were no other notable real-world benefits to these downsized engines.

Few drivers needed all of the V8's output continually though - a fact which American engineering giant and automotive supplier Eaton had been mulling for some time, in an effort to get ahead of future regulations. One particular problem that it had identified was that of 'throttling loss'.

During a steady-state cruise, or at small throttle openings, the engine would experience a high throttling loss - because a considerable amount of energy would have to be expended to draw the fuel-air mix through the small opening in the carburettor or throttle body. The cylinders would also not receive a full fresh charge during each intake stroke, resulting in inefficient combustion.

This would cause poor efficiency during general driving. Fitting a smaller engine with fewer cylinders was one way around this but the performance implications were obvious and not ideal for many of the luxury or high-performance brands.

Consequently, Eaton had been exploring the concept of cylinder deactivation - reputedly since the early '70s - as a way to fulfil both economy and output criteria. Running the engine on fewer cylinders would require the remaining cylinders in operation to work at a higher power level, in order to maintain output, which would also require the throttle opening to be larger.

Because fewer cylinders would be drawing through a larger opening, throttling losses would be significantly reduced, the conditions in the cylinders would be optimised and efficiency would climb. When more power was required, the other cylinders could be brought back online.


Doing so effectively would, according to Eaton, require that the offline cylinders' intake and exhaust ports remain closed. This would avoid pumping losses and the cooling of the combustion chamber, which might introduce issues if the cylinder was needed to fire again.

Eaton wasn't the only company exploring this idea but it had developed a 'Valve Selector' system that allowed cylinders to quickly and easily be 'switched' off and on. Atop the selector-equipped cylinders' rocker arm fulcrums was a solenoid-controlled, spring-loaded body. During normal operation, the selector body would be locked in place on its mounting stud and the rocker would operate conventionally - the cam lobe would act on the pushrod, the pushrod would act on the rocker arm, the rocker arm would pivot on its fulcrum and then open the valve.

When the selector's solenoid was energised, however, a blocking plate would be retracted. This would allow the spring-loaded body to float on the rocker's stud. When the rocker arm was lifted by the pushrod, the fulcrum would simply ride up the stud - and the head of the rocker arm would instead pivot on the tip of the valve stem and the valve would remain closed.

The system would, of course, have to be fully integrated into the vehicle's engine management and control systems in order to function properly - but the potential benefits were significant. In 1980, Eaton claimed a 40 per cent improvement in fuel efficiency at idle and during deceleration, while low-speed and motorway cruising efficiency gains were tallied at 25 and 15 per cent respectively.

Benefits were also noticeable on the emissions front; in eight-cylinder mode the 6.0-litre V8 prototype put out 377g/km of CO2. In four-cylinder mode, that figure fell to 336g/km. Reductions in NOx and hydrocarbon emissions were also possible, lending the technique further appeal.

Cadillac, having tested the system in prototype form, decided that this was the way forward - and, in conjunction with Eaton, developed the 'Modulated Displacement' V8-6-4 L62 V8. This electronically controlled, throttle-body injected V8 displaced six litres and produced 140hp and 265lb ft. A pair of cylinders on each bank was equipped with Eaton's Valve Selectors, allowing the engine to also run in six- and four-cylinder configuration; this process was entirely automatic and, in the cabin, an 'MPG Sentinel' would display fuel consumption and the number of cylinders currently operating.


As the engine load decreased, the number of operational cylinders would be similarly reduced - with each being shut off before the exhaust cycle; this trapped hot gas would keep the cylinder warm while the high pressure would also prevent oil creeping past the rings.

The engine could run in 4.5-litre V6 configuration or 3.0-litre V4 set-up and, overall, the EPA stated that L62 would average 18 imperial miles to the gallon in the city and 28mpg on the highway. The older 7.0-litre engine, for comparison, would return around 16mpg and 24mpg respectively. Cadillac had so much faith in its new cylinder deactivation system that, in a bold move, it was made standard across its entire range in 1981.

Unfortunately, the potential benefits were outweighed by the fact that - in the real world - the system transpired to be miserably ineffective and unreliable. The control and fuel delivery systems were simply not advanced enough to enable smooth and sensible transitions between the various cylinder modes, resulting in poor running and fuel consumption that was often equivalent to conventional engines.

Most owners promptly had the system disabled and the V8-6-4 option was quietly and quickly dropped from the vast majority of Cadillac's line-up just a year later - in part, on the flip side, because improvements in electronic fuel injection and other emissions systems made the complicated V8-6-4 set-up redundant.

As the technology advanced, other manufacturers - including Mitsubishi and Mercedes-Benz - began to employ displacement-on-demand systems as a way to boost economy, reduce emissions and maintain performance. Later developments, including advanced cam and valve control systems that operated far more quickly, further made the technology more viable and less obtrusive. Cadillac's parent company, General Motors, would ultimately wait until 2005 to begin using the system again.

At any rate, while Cadillac's V8-6-4 was the first mainstream automated system of its kind, it was not the first cylinder deactivation set-up. The Enger Motor Car Company, based in Ohio, had introduced a new overhead-valve, cam-in-block V12 called the 'Twin-Unit Twelve' in 1916. The 3.7-litre, 60-degree V12 produced 56hp and was claimed capable of averaging a stellar 38mpg when driven with efficiency in mind - thanks to its 'Economy Lever'.


When the driver pulled on the Twin-Unit Twelve's Economy Lever, a solenoid-operated system would hold open the exhaust valves on one bank of the V12 while simultaneously closing a flap in the intake manifold, preventing fresh charge reaching the cylinders. This engine, the deactivation system of which was also patented in 1916, was claimed by Enger to offer 'More Power, More Get-a-Way, More Speed, More Economy'.

Edward L. Jones, who designed the system, said: 'All the cylinders may be used when great power is required and a fewer number of cylinders when a smaller amount of power is required. With such means the motor is found to work at a high efficiency with a light load, resulting in marked economy in the consumption of fuel.' Alternating between a V12 and effectively an inline six-cylinder configuration also ensured that 'the motor is practically free of vibration'.

Even Enger, however, was seemingly beaten to the punch. The Sturtevant Mill Company, which produced the world's first automatic transmission, had reputedly conceived a cylinder deactivation system as early as 1904. According to a report from 'The Horseless Age' - the first American magazine to begin covering the era of internal combustion-powered transport - from the same year, Sturtevant was set to produce 'an eight-cylinder horizontally opposed motor developing about 24hp.

'It will be designed,' it added, 'so that four cylinders can be cut out when the full power of the motor is not required'. Details on this are few and far between, although it is suggested that it had twin magnetos and a system to lock open the exhaust valves on one bank.

It's also claimed that Sturtevant produced a 38-45hp flat-six engine - although some adverts from the time state 38-40hp - that is said to have made use of this system. Despite Sturtevant having submitted patents for many other elements of its automotive-related innovations, however, seemingly no details remain on file regarding this potential innovation.

Regardless, Sturtevant ceased its automotive endeavours in 1908, leaving others to capitalise on the growing automotive market and - later down the line - cylinder deactivation systems.

P.H. O'meter

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Comments (18) Join the discussion on the forum

  • simonrockman 04 Jun 2018

    In a modern engine, would it be possible to have cylinders of different capacities.

  • helix402 04 Jun 2018

    The E32 750i/il could run on 6 cylinders.

  • Krikkit 04 Jun 2018

    simonrockman said:
    In a modern engine, would it be possible to have cylinders of different capacities.
    Yes : https://www.youtube.com/watch?v=A6H66xfEZC4

    Edited by Krikkit on Monday 4th June 17:19

  • Jimmy Recard 04 Jun 2018

    helix402 said:
    The E32 750i/il could run on 6 cylinders.
    On demand, in the pursuit of fuel economy or just if it had to?

    Plenty of engines do as a failsafe - Cadillac’s Northstar would be another notable example.

  • djdest 04 Jun 2018

    My mate has a V12 Merc coupe (no idea of the model) that is twin turbo and approx 700bhp.
    It reduces from V12 to V10 to V8 to save fuel.
    The economy surprised me a lot, a trip to central London and back used half a tank (250 mile round trip). My V6 biturbo 500bhp Audi S4 I had at the time would have easily used a full tank

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