1981 Cadillac Sedan de Ville and Its V-8-6-4 Make Big Promises

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1981 Cadillac Sedan de Ville and Its V-8-6-4 Make Big Promises


From the April 1981 issue of Car and Driver.

Seems no one wants to ride the range in a Cadillac anymore. The favorite steed of wealthy Texas ranchers and filthy-rich urban cowboys is taking it in the ear. In calendar year 1980, Cadillac sold about half as many cars as it had in 1979. And the prospects for this season are only a little better.

Even given America’s distaste for big cars, this state of affairs is surprising. Cadillacs, after all, are in a different league from full-sized Chevys and Fords. For one thing, they cost half again as much. And anyone who can af­ford to sink seventeen grand into a car couldn’t be worried about paying for the gas. You’ll note that the 1973 oil cri­sis didn’t even put a downward blip in Cadillac’s sales chart. And Mercedes­-Benz and BMW have had no trouble peddling their megabuck big cars—cars that deliver about the same mileage as the Cadillac.

So it just may be that Cadillac is a vic­tim of its own decadent image. A Caddy just isn’t the kind of car you want parked in the driveway if you harbor any aspirations of appearing socially re­sponsible and energy-conscious.

The Cadillac Division has been trying to undo this fall from grace by injecting its line with a dose of efficiency. A 5.7-liter diesel V-8 that boosts mileage to over 20 mpg is now available across the board. And last year Cadillac began of­fering a 4.1-liter, gasoline-fired V-6. This year’s new economy improver, and the reason for this report, is truly a step into fresh technological territory: the world’s first variable-displacement en­gine.

In simple terms, the V-8-6-4, as the engine is called, runs on four, six, or eight cylinders, depending on power demand—which would logically maxi­mize economy [see Technical Highlights, below, for details]. Cadillac hopes that this golly­-gee-whiz engineering will prove for once and for all that it is in the forefront of fuel efficiency, that the days of excess are over. No doubt that’s why it went ahead with the system knowing full well it would deliver only 15 mpg on the EPA driving cycle—less than either the V-6 or the diesel engine offering.

None of this is meant to imply that the V-8-6-4 is a bust. It does improve mileage. According to Cadillac, EPA city mileage in some models is up 1 mpg over last year’s V-8. And in real-world, 55-to-60-mph highway cruising, Cadil­lac maintains the system delivers a 3-to-4-mpg benefit.

If nothing else, the system is admira­bly refined. Our Victorian Plum Fire­mist Sedan de Ville d’Elegance was a model of civility. Cadillac has scienced out the V-8-6-4 concept well enough that it operates almost unnoticed most of the time. The V-8-6-4 idles and moves off from rest on all eight cylin­ders, dialing back to six or four when speed levels off. Anything approaching even moderate acceleration calls all eight cylinders back to work.

In our test car, all of this happened far more smoothly than an automatic transmission can shift gears. In fact, the transitions between four-, six-, and eight-cylinder operation were so subtle that most passengers didn’t have a clue they were taking place. Behind the wheel, though, the system is a little more obvious. Sensitive drivers will no­tice a soft push in the back as extra cyl­inders kick in. And with the cruise con­trol set at 65 mph the engine continual­ly hunts between four and six cylinders, looking for optimum efficiency.

Just to make sure even the most obliv­ious of drivers know what hi-tech drama is playing out under the hood, every V-8-6-4 is equipped with what Cadillac calls an MPG Sentinel. This digital-­readout instrument keeps track of active cylinders as well as miles to empty and instantaneous and average mpg.

While all of this Space Age wizardry is guaranteed to keep even tech-heads entertained (it’s now Cadillac’s biggest­-selling powerplant), the fuel-economy benefits it produces are less than amus­ing. After more than 1500 miles, our test de Ville returned an embarrassing 11 mpg. Even taking into account the cold weather and the C/D staff’s collec­tive lead foot—which kept the engine running on eight hungry cylinders most of the time—the results are still nothing to write to OPEC about.

But if the V-8-6-4 system fails to re­peal the physical laws, which state it takes a lot of energy to haul 4240 pounds around, that still doesn’t mean the Cadillac is without worth. It does, after all, represent something of a high­-water mark for conventional American sedans. It’s the biggest, roomiest, smoothest-riding, quietest, most luxuri­ous car mighty General Motors knows how to build, the culmination of dec­ades of development of the front-engine, rear-drive automobile.

Truth be known, the Cadillac is as im­pressive in its own way as a Mercedes­-Benz is in its. While Mercedes are re­nowned for their confidence-inspiring road feel and reassuring handling, the Cadillac is a masterly exercise in the art of isolation.

Cadillac expends no small amount of engineering effort refining its version of GM’s full-sized car. Each different body style receives its own unique suspension bushings, shock-absorber valving, spring rates, body mounts, and engine mounts. Special structural braces not used on any other GM sedans (our de Ville had one across the trunk wall) tune out body resonances and reduce tire boom across tar strips. Brake pads have been specified for quietness, and Cadil­lac has strict standards for tire roundness to ensure the best possible ride. And of course Cadillac ladles on enough gooey sound deadener to quiet a Saturn booster.

The result of this tuning is a car that’s incredibly hushed, and pure velvet on smooth roads. Tar strips and pavement blemishes all but disappear, and it even handles moderate bumps with a fair amount of discipline. The de Ville also proves surprisingly agile for so large a car, in part because of the inherently good handling of GM’s full-sized chas­sis. Of course, trying to follow your neighbor’s Mercedes down bumpy country roads will set the Cadillac to flopping around—but then again, it was never intended as a driver’s car.

Its mission in life is to take the pain out of travel, and that it does. Our de Ville’s plum-colored Soft Venetian Ve­lour interior—with its overstuffed, loose-pillow couches, acres of pseudo wood, and numerous splashes of chrome—looked like a cross between Louis XIV’s boudoir and a high-class S&M parlor. But it was comfortable, thanks to all that room and the front seats’ six-way power adjusters and elec­tric recliners.

These days, de Villes come equipped with almost every option a sane man could want, including a digital display, electronic climate-control system and a mean-sounding, four-speaker, digital­-display AM/FM-stereo/clock. Of course, that’s never stopped Cadillac from offering every option that man, in his most wildly imaginative moments, has ever dreamed up.

Our test de Ville, for instance, was loaded down with nearly four grand worth of such filthy-rich-person luxo­gear. The list includes such indispens­able pieces as wire wheel covers, opera lamps, a Twilight Sentinel to turn the headlights on and off, and a Guidematic automatic dimmer (God forbid you should have to dim the lights yourself).

None of this is news, really. Cadillacs have always oozed this brand of luxury. And except for the hard reality of the energy crunch, they probably always would have. For better or worse, that’s not to be. In a serious bid for survival Cadillac will introduce its first small car, a version of the Accord-sized, front­-drive-J-car, in a matter of months. By all indications, it won’t be long before the biggest, baddest American luxocruiser goes the way of the cowboy.


Technical Highlights

Downsized Caddys are still a few years off, and in the interim the division is doing everything it can to squeeze the utmost efficiency from its large gasoline powerplants. Last year, the big V-8 was reduced to six liters and given computer-controlled electronic fuel injection. This year variable displacement was added which, in theory at least, should further mitigate its thirst for fuel.

The variable displacement is achieved by selectively rendering cylinders inoperative. The cylinder selection is controlled by a central microprocessor, which also controls fuel flow (via twin throttle-body-mounted injectors), ignition timing, exhaust-gas recirculation, idle speed, and air-pump operation. To make the correct decisions, the computer must be supplied with accurate information about the engine and the car. This is done by a network of sensors that monitor intake-manifold pressure, ambient pressure, coolant temperature, manifold-charge temperature, engine rpm, vehicle speed, transmission ratio, throttle position, and exhaust-gas composition.

Armed with this vast knowledge, the computer selects the proper number of cylinders for optimum fuel economy, emissions, and drivability. During idle, deceleration, low speed, cold running, and anything but light acceleration, the engine pumps away on all eight cylinders. During cruises, when the computer senses that the eight cylinders are loafing, it shuts two of them off, forcing the remaining ones to work harder. If the load is still too light, it shuts off two more, turning the powerplant, effectively, into a three-liter V-4. With fewer cylinders working harder, intake manifold vacuum decreases, reducing pumping losses, which is the work required to draw the air-fuel mixture into the cylinder against this vacuum. The result is greater thermal efficiency and improved fuel economy.

The magic of cylinder selection is performed with Eaton valve selectors that disable cylinders by keeping their valves closed. The valve selectors are solenoid-actuated devices located above the rocker arms inside the valve cover. Depending on the solenoid’s position, a blocker plate is rotated into or out of alignment with projections on the valve-selector body. When they are not in alignment, these projections bear against the blocker plate, preventing any vertical motion, and the rocker arm operates normally, pivoting at its center. When the projections and holes are in alignment, the selector body, along with the rocker pivot, is free to move up. Thus the upward motion of the pushrod causes the rocker arm to pivot about the valve stem, and the valve remains closed. Each selector controls one pair of intake and exhaust valves. With its valves closed, the cylinder no longer draws fresh air-fuel mixture, but merely compresses and expands whatever charge is trapped inside.

Despite the sterling theory, the result is not exactly earth-shattering. The 1981 Sedan de Ville’s EPA city and highway fuel-economy numbers, 15 and 23 mpg respectively, are identical to those of last year’s fixed-displacement car. Some of this is due to the shorter axle ratio (2.41 versus 2.28) used this year for improved acceleration. But mostly it is due to the EPA’s driving cycles, in which the engine spends most of its time in the eight-cylinder mode. At very steady, moderate speeds, where some cylinders are shut off, there is a benefit, but comparatively little driving is done in that fashion, either in the EPA cycle or in the real world.

Which makes one wonder why Cadillac bothered. Porsche, Mercedes, and BMW are all working on their own variable-displacement schemes, and on their higher-powered cars it may work better. But Ford worked on both six- and eight-cylinder variable-displacement engines for years and never produced them because there was too little fuel-economy benefit. One suspects that Cadillac knew this all along, but felt it had to give its cars a sophisticated, fuel-efficient image. The high tech certainly does that, but both C/D observed and EPA fuel economies show that the Sedan de Ville has not yet shed its gas-guzzling tradition. —Csaba Csere

Specifications

Specifications

1981 Cadillac Sedan de Ville
Vehicle Type: front-engine, rear-wheel-drive, 6-passenger, 4-door sedan

PRICE

Base/As Tested: $13,847/$17,685
Options: d’Elegance package, $1005; AM/FM-stereo 8-track radio with CB, $480; wire wheel covers, $266; vinyl roof, $240; metallic paint, $208; electronic level control, $173; other, $1466

ENGINE
pushrod V-8-6-4, iron block and heads, electronic fuel injection

Displacement:
8-cylinder mode: 368 in3, 6040 cm3
6-cylinder mode: 276 in3, 4530 cm3
4-cylinder mode: 184 in3, 3020 cm3
Power: 140 hp @ 3800 rpm

Torque: 265 lb-ft @ 1400 rpm 

TRANSMISSION
3-speed automatic

CHASSIS

Suspension, F/R: control arms/trailing arms

Brakes, F/R: 11.7-in vented disc/11.0-in drum

Tires: Firestone 721 Steel Belted Radial
215/75R-15

DIMENSIONS

Wheelbase: 121.4 in

Length: 221.0 in

Width: 76.5 in
Height: 55.6 in

Passenger Volume, F/R: 56/55 ft3
Trunk Volume, Behind F/M/R: 20 ft3
Curb Weight: 4240 lb

C/D TEST RESULTS

60 mph: 11.6 sec
1/4-Mile: 18.4 sec @ 75 mph
90 mph: 31.6 sec

Top Gear, 30–50 mph: 5.4 sec

Top Gear, 50–70 mph: 8.9 sec

Top Speed: 101 mph
Braking, 70–0 mph: 233 ft

Roadholding, 200-ft Skidpad: 0.63 g 

C/D FUEL ECONOMY

Observed: 11 mpg

EPA FUEL ECONOMY

Combined/City/Highway: 17/15/23 mpg 

C/D TESTING EXPLAINED

Headshot of Rich Ceppos

Rich Ceppos has evaluated automobiles and automotive technology during a career that has encompassed 10 years at General Motors, two stints at Car and Driver totaling 20 years, and thousands of miles logged in racing cars. He was in music school when he realized what he really wanted to do in life and, somehow, it’s worked out. In between his two C/D postings he served as executive editor of Automobile Magazine; was an executive vice president at Campbell Marketing & Communications; worked in GM’s product-development area; and became publisher of Autoweek. He has raced continuously since college, held SCCA and IMSA pro racing licenses, and has competed in the 24 Hours of Daytona. He currently ministers to a 1999 Miata, and he appreciates that none of his younger colleagues have yet uttered “Okay, Boomer” when he tells one of his stories about the crazy old days at C/D.



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