In 1981, Cadillac rolled out a new version of its 368-cid V-8 engine with a “modulated displacement” (cylinder deactivation) system that let it run on eight, six, or four cylinders under different conditions. Dubbed the “V8-6-4” engine, Cadillac called it “a prime example of American innovation in action,” but its poorly driveability and poor reliability soon left Cadillac with a host of angry owners, outraged dealers, and class-action lawsuits. However, contrary to popular belief, those ills were NOT why the V8-6-4 engine disappeared from most models after only one year.
What GM called “modulated displacement” is today more commonly called “cylinder deactivation,” which better describes the idea: shutting off certain cylinders of an engine under light or moderate load as a way of saving fuel. Cylinder deactivation is not uncommon on modern cars and light trucks. The EPA reported that about 15 percent of U.S.-market light vehicles used it in the 2023 model year.
The cylinder deactivation system Cadillac adopted for 1981 was based on a series of 1975 patents by the Eaton Corporation. Four of the engine’s eight cylinders had solenoid controls that could disengage the rocker arms at the fulcrum, preventing the intake and exhaust valves on that cylinder from opening. The piston would still move, compressing the air in the cylinder, but no fuel could enter the cylinder. The system was programmed so that cylinders would be deactivated in pairs, beginning with the 1 and 4.
Ford had experimented with its own cylinder deactivation system based on the same patents, but they found it was difficult to manage the transition with mechanical controls. Cadillac integrated the modulated displacement system into its “Computer Command Control” digital engine management system, which also controlled spark timing and throttle body fuel injection, with speed-density metering based on manifold absolute pressure with oxygen sensor feedback control. (This was NOT the Bendix injection system offered on the 1975–1979 Seville, which was an analog port injection system.)
The V8-6-4 engine started on eight cylinders and could cut back to six or four cylinders under light load (although brand-new engines that weren’t yet broken in would rarely run in four-cylinder mode). Pressing the accelerator would reengage the deactivated cylinders in the same order they were deactivated. A display option on the standard MPG Sentinel digital fuel consumption meter would show how many cylinders were currently operating. The engine management computer also had various self-diagnostic and limp-home features, with a “Check Engine” light that illuminated if the computer detected a fault.
1981 Cadillac V8-6-4
Cadillac installed the modulated displacement system on its 368-cid (6,040 cc) V-8 engine for 1981. (GM and the EPA officially identified this engine by its 6.0-liter metric displacement, but Cadillac fans more often call it the 368.) Known on the order form as the L62, it was the last descendant of the 1968-vintage Cadillac 472/500/425 engine family, de-bored to 3.80 inches. In 1980, the L62 engine was offered in both carbureted and injected form, but for 1981, the carbureted version was limited to the commercial chassis. The injected version now had 140 hp and 265 lb-ft, down 5 hp and 5 lb-ft from 1980.
The 6.0 liter V8-6-4, as it was described in Cadillac brochures, was standard on all 1981 Cadillac models except the Seville, where the 368 was a no-cost alternative to the standard Oldsmobile diesel V-8. Most models could also be ordered with the six-cylinder LC4 engine, a Buick 90-degree V-6 bored to 252 cid (4,128 cc), as a credit option
Although Cadillac had downsized its C-body full-size models for 1977 and the Eldorado for 1979, these were still big cars with curb weights well over 4,000 lb, and V-8 models all had a tall 2.41 axle ratio. Performance was sluggish with the diesel or the Buick V-6, adequate with the V8-6-4: Car and Driver recorded 0 to 60 mph in 11.6 seconds and the quarter mile in 18.4 seconds at 75 mph with a 1981 Sedan de Ville with the 6.0-liter engine.
Before launch, GM had claimed that the cylinder deactivation system could improve overall fuel economy by up to 7 percent. Cadillac chief engineer Bob Templin boasted that the system could be good for an improvement of 4 to 5 mpg on the highway — a preposterous claim that bordered on false advertising — and asserted that modulated displacement was worth “more than an overdrive system.” (I can’t help wondering if he was feeling touchy that the new GM four-speed overdrive automatic transmission was available only on RWD V-6 cars for 1981.)
Outside of the delirious realm of pre-launch hype, the promised fuel economy benefits of the modulated displacement engine were much harder to spot. Readers of the 1981 EPA Gas Mileage Guide found that the city rating of a De Ville or Fleetwood Brougham with the V8-6-4 engine was still only 15 mpg, the same as the carbureted 1980 6.0-liter cars. Detailed EPA test data shows that the combined mileage of a 49-state 1981 De Ville or Fleetwood with the V8-6-4 was actually 0.7 percent lower than a 1980 model with the 368 and no cylinder deactivation (albeit not enough lower to reduce the window sticker ratings). California De Ville/Fleetwood models were up by 1.18 mpg, an improvement of about 7.2 percent. The 49-state Eldorado and Seville were up by 0.72 mpg, an improvement of 4.3 percent, while California models were up 0.69 mpg, a 4.2 percent gain.
For Cadillac, the real importance of these slight improvements was that they kept the 1981 cars from incurring a federal gas guzzler tax. In 1980, the tax was only imposed on new cars with an EPA combined mileage of less than 15 mpg; for 1981, the threshold increased to 17 mpg. Falling below that threshold would incur a tax of at least $200 per car (a relative worth of over $900 in 2025 dollars!), something GM was keen to avoid. (There were several GM vehicles in this period that would have been subject to the gas guzzler tax had they not been exempt for other reasons, such as the Chevrolet Impala/Caprice with the four-barrel 350 police engine, which was exempt if initially sold to an actual police agency.)
I should stress that the gas guzzler tax was an entirely separate consideration from Cadillac’s impact on GM’s Corporate Average Fuel Economy (CAFE) calculations. For 1981, GM needed to achieve a sales-weighted average of at least 22 mpg to avoid civil penalties. CAFE was calculated across the whole corporation, not by division, but Cadillac was still a consequential chunk of total GM passenger car sales, accounting for 1 in every 19 GM cars in 1980 and about 1 in every 17 cars in 1981, so anything the division could do to improve the fuel economy of its cars was helpful. (That’s why Cadillac continued to push the awful Olds diesel, and why they offered the Buick V-6: Both engines had EPA combined ratings of over 20 mpg, which helped to balance the cars powered by the thirstier gas V-8 engines.)
Reliability Woes and Lawsuits
Had the V8-6-4 engine otherwise worked as advertised, probably no one would have been too upset about its still-mediocre mileage, but it quickly became clear that the system had come out of the oven way too soon. Credulous testers like Jim Dunne of Popular Science, sampling carefully prepared cars on the GM Proving Grounds, claimed the transitions from eight to six to four and back were almost imperceptible, but in the real world, changes between modes were often marked by pronounced hesitation and surges. The switch back to eight cylinders was sometimes also accompanied by momentary spark knock as the engine computer recalculated the correct ignition timing. The uneven firing intervals when cruising in six-cylinder mode, meanwhile, created a roughness that could be mistaken for an unbalanced wheel, leading customers to complain that V8-6-4 cars rode unusually poorly.
Some of the engine’s problems were actually due to the problems with the fuel injection system. Bob Templin proclaimed throttle body injection “the greatest thing since canned beer” (a fascinating comparison for those of us who find canned beer repulsive), but Cadillac had many problems with leaking or sticking injectors (the first problem was allegedly fixed early on, the second was not), and the system was prone to icing in the intake manifold and MAP sensor pipe. These problems were likely responsible for at least some of the hesitation and stalling that owners experienced.
Another, more endemic problem was that because the throttle body injection system had only one injector per cylinder bank, there was no way to cut off the flow of air-fuel mixture to deactivated cylinders. In six- or four-cylinder mode, excess fuel would collect around the intake valves of the deactivated cylinders, which then caused momentary over-richness when those cylinders reactivated. This might have been avoidable with port injection, but Cadillac had already abandoned that as too expensive. (Cadillac engines wouldn’t adopt port fuel injection again until 1990.)
Also, in 1981, the concept of the “Check Engine” light was new, and its behavior was annoying to owners and confusing to dealer technicians, who would sometimes replace components multiple times because they had neglected to clear the error codes from the computer after making a repair and thus assumed that the fault still existed. Some owners were troubled to learn that if they didn’t take the car for service promptly enough (within 30 engine starts), the computer would flag them for negligence — which could be used to deny warranty coverage — and that the engine computer also flagged each time the car was driven above 85 mph.
Cadillac acknowledged the injector and icing problems, but initially blamed the rest on uneducated owners and poor dealer service. Templin even suggested that owners might be causing the problems themselves by installing electronics that weren’t factory approved, like aftermarket CB radios or car phones. However, a Cadillac dealer service bulletin subsequently admitted that most of the driveability problems were normal, and advised dealers not to “inconvenience” the customer by trying to fix them.
Customers were none too happy about that, while dealers screamed that the whole engine management system (including the fuel injection system) was too complicated to diagnose and fix. Some dealers assumed that the fuel injection system was the same one previously used on the Seville — it wasn’t — and demanded to know why Cadillac still hadn’t fixed it. Before long, unhappy owners were filing lawsuits. Cadillac tried to placate them and squelch the “unwarranted adverse publicity” by offering an extended five year/50,000-mile warranty on the whole engine control system, but the most disgruntled customers were not mollified. GM eventually faced class-action suits over the V8-6-4 engine in more than a dozen states.
These legal battles were further inflamed by Cadillac’s admission that the V8-6-4 engine would no longer be offered after the 1981 model year except on the Fleetwood limousine. Aggrieved plaintiffs added this to their legal complaints, contending that they had essentially paid to beta test an experimental engine that was neither safe nor fit for purpose. Some of the lawsuits dragged on for years.
It was easy to simply disable the modulated displacement system, leaving the engine running in eight-cylinder mode all the time, but Cadillac warned that doing so would void the warranty. It was probably also illegal for a dealer or mechanic to do it on a customer car — it would likely count as tampering with emissions control equipment, which federal law prohibits — but quite a few did it anyway.
The Actual Reason the V8-6-4 Was Dropped
Despite all that, Cadillac did NOT drop the modulated displacement system because of its driveability and service problems, or because of the lawsuits. As Cadillac stated at the time, the decision to only offer it for one year (except on the low-production limousine) had actually been made before the 1981 models were even launched.
Cadillac offered two explanations for the decision to drop the V8-6-4, one of which was probably partly true and the other mostly false.
The explanation Cadillac gave dealers was that even with the modulated displacement system, there would be no way for the 6.0-liter engine to avoid the gas guzzler tax after 1981, since the 1982 threshold was set to rise from 17 mpg to 18.5 mpg. That part was likely true: None of the 1981 V8-6-4 cars could manage even 18 mpg combined, and it’s unlikely that they would have done much better for 1982. If the 49-state De Ville/Fleetwood Brougham had maintained the same EPA combined mileage as in 1981, it would have been subject to a $350 gas guzzler tax for 1982 and a $500 tax for 1983. (The Fleetwood limousine, which retained the V8-6-4 through 1984, only escaped the gas guzzler tax because its gross vehicle weight rating exceeded 6,000 lb, making it exempt; otherwise, it would have faced a $2,150 tax by 1984.)
Bob Templin, meanwhile, claimed publicly that the reason for dropping the V8-6-4 was that the EPA had refused to grant a waiver of the federal carbon monoxide (CO) standard. This was a falsehood wrapped in a half-truth: It was true that GM had applied for an EPA waiver, claiming that the modulated displacement engine couldn’t pass the EPA 50,000-mile durability test at the 1981 standard (3.4 grams/mile CO) without an extra year of work on the control systems. It’s also true that the EPA had denied the waiver request in July 1980, saying that there was no technological reason the modulated displacement engine couldn’t comply with the 1981 standard (as in fact it eventually did).
However, the EPA decision (which was published in the Federal Register and is a matter of public record) makes clear that GM had only requested a waiver for 1981, NOT for 1982 or later years. And, while GM argued that it was in the public interest to grant them a waiver so they could get additional field experience with the cylinder deactivation technology, EPA administrator Douglas M. Costle noted:
GM representatives were not aware of any GM production vehicles which would utilize modulated displacement technology in model year 1982 or beyond. … The lack of future modulated displacement applications leads the EPA technical staff to believe the level of effort expended on solving the control systems problem may have been somewhat limited. [Emphasis added.]
In other words, the EPA had refused to grant a waiver for 1981 (in part) because GM had already admitted that it had no plans to use the modulated displacement technology in 1982 or beyond, not the other way around.
Also, while Templin blamed the disappointing fuel economy of the V8-6-4 engine on the recalibration needed to meet the 3.4 g/mile CO standard, Costle pointed out that GM officials had testified that “they do not anticipate a significant fuel economy penalty” in meeting the CO standard, and that “GM did not establish costs, driveability, or fuel economy as issues affecting the availability of technology for this engine family.” Costle had therefore concluded that it was “not essential to the public interest or to the public health and welfare” to allow Cadillac to sell cars producing more than twice as much CO as most other new cars (7.0 grams/mile rather than 3.4 grams/mile) just to give GM additional “field experience” with a new engine technology they MIGHT conceivably use again at some unspecified future time.
While Templin’s claims were disingenuous at best, they were also ultimately irrelevant: The actual reason Cadillac dropped the V8-6-4 (except on the low-production limousine, which retained it through 1984) was that the division was already preparing to launch the new aluminum-block HT4100 V-8 for 1982.
A lot of Cadillac histories, and even some contemporary accounts of the V8-6-4 saga, give the impression that Cadillac hastily pulled the HT4100 out of a hat in response to problems with the V8-6-4. This of course was not true at all: The all-new engine had been in the planning stages since the mid-’70s, and its development had been common knowledge in Detroit since at least the beginning of 1979. For a while, there was some uncertainty about its exact launch date because the new engine was to be produced in all-new, more heavily automated engine plant in Livonia, Michigan, about 15 miles outside Detroit. At the time GM applied for the 1981 EPA waiver for the 6.0-liter modulated displacement engine, completion of that plant was less than a year away. Once tooling was completed, HT4100 production would begin in July 1981.
Therefore, even if the modulated displacement system had been completely reliable, the V8-6-4 engine would have only been a temporary stopgap, and its days were numbered as soon as GM authorized construction of the new Livonia plant. The 368 was assembled at the existing engine plant in Detroit, which Cadillac was preparing to phase out, along with the 6.0-liter engine itself. (Although a few cars continued to use it through 1984, production of 1982 to 1984 Fleetwood limousines with the V8-6-4 totaled only 3,093 cars in three years; sources differ on the number of commercial chassis with carbureted 368 engines, but it was surely even fewer than that.)
The HT4100 V-8 would turn out to have many problems of its own, and the original version was painfully underpowered, but it was 209 lb lighter than the 6.0-liter engine, and its EPA mileage was much better. Since the HT4100 had a lot less torque than the 368 and was mated to a four-speed automatic with a tall overdrive gear, adding the modulated displacement system wouldn’t have gained much. As Jim Dunne had explained in the October 1980 Popular Science:
Cadillac does not see the variable-displacement concept working in small engines. The 368-cu.-in. V8 in the Cadillac—the biggest displacement engine available on any American car—works fine because it never really taps its full power potential. In smaller engines, there is less margin to tap, so there’s less gain in fuel economy.
Based on Automotive News data, Cadillac sold 165,611 ’81 cars with the V8-6-4 engine, not including an additional 1,200 1981 Fleetwood limousines. Purchasers of those cars who complained that they were basically experimental guinea pigs weren’t wrong: They had paid high prices for an engine that had more bugs than a Florida picnic, which apparently couldn’t deliver its claimed fuel economy benefits while still meeting 1981–1982 emissions standards, and that its manufacturer had decided to drop before the engine even went on sale.
Eventually, cylinder deactivation would become reasonably reliable (56 percent of U.S.-market GM vehicles used it in 2023), but I don’t think many unhappy Cadillac V8-6-4 owners would have found that very reassuring back in 1981.
Related Reading
CC Video Classic: 1982 GM HT 4100 Engine Promotional Video – World Record Razzie Winner? (by Jim Brophy)
Thanks for the in-depth guidance on the V8-6-4 and the politics involved. I do remember reading about it and the diesel and wondering where GM was headed in the early 80’s. Then the HT (Hook & Tow) 4100 came out with its own issues. The NorthStar was no saint either. Cadillac tarnished its image and did permanent damage. Many customers never looked back.
Another engine failure was the Chrysler fuel injected 318 via the ’81 to ’83 Imperial (a story of its own).
Somehow, Ford kept the 302 (5.0 litre) rolling along via electronic engine management, then TBI, then multiport injection; then the modular V8, and won the domestic luxury car battle with the Town Car. What a cash cow!!
Today, GM engines are generic as possible where the same engine can be found in a Cadillac and a Chevrolet as engine development is so expensive. You would think they have learned their lesson by now. Yet, I still hear about GM engine issues like stretched timing belts and GM fighting the customer tooth and nail.
I’ve only owned one GM car which had the indestructible 231 V6; slow as hell, but reliable.
However, never entertained owning another GM vehicle in subsequent car purchases based on its tarnished history.
GM is currently having issues with 5.3 and 6.2 liter engines that are found in pickups, Suburbans, and Cadillac Escalades.
There are several 5.3 liter engines in fleet pickups where I work and they are starting to have issues. One had the camshaft disintegrate at 60,000 miles. When it was dumped off at the dealer, there was a row of similarly affected pickups sitting behind the building.
Chrysler has also experienced these issues with its Hemi and its MDS system. Ford hasn’t seemed to have issues with the Coyote V8 since it introduced a similar system in 2021, but then again they may have other issues with the wet belt drive for the oil pump, also introduced to the Coyote at the same time. FWIW, the 6.2L V8 issues highlighted today by the media and subject to the recall are not related to the Dynamic Fuel Management system, but rather to crankshaft failures.
When we bought our 18 Sierra, i almost immediately got an override block for the cylinder deactivation system. Bought from Amazon it worked very well.
One of the many reasons why long term, loyal Cadillac owners “defected” to Lincoln and never returned to the General Motors family.
I love that letter from Cadillac. “Dear Cadillac owner: there is nothing wrong with our car, and all of your whining is unreasonable. But because you are so annoying, we are increasing warranty coverage. Now shut up.”
The whole CAFE system irritated me in the early 80s and it still does. If the government had set out to hobble the US auto industry while largely leaving foreign manufacturers alone, they could hardly have come up with a more effective system.
Yes, I found that breathtakingly patronising. And I had to smile at the first sentence; outside North and possibly South America, the Cadillac name was something of a historical curiosity by then rather than being “a symbol of automotive excellence”.
Wow, what an interesting story. Never knew that many details about it. Sounds like that Templin guy should have been arrested and put in jail!
I had a Steel Blue 1981 Eldorado with the V8-6-4 as a used car from 1990-92. I’ve said before that in 8 or 4 cylinder mode it ran fine, but 6 cylinder mode provided a perceptible “shake” or vibration through the car. So I’d agree with this statement: “The uneven firing intervals when cruising in six-cylinder mode, meanwhile, created a roughness that could be mistaken for an unbalanced wheel, leading customers to complain that V8-6-4 cars rode unusually poorly.”
That said, I was amazed the electronics still worked with no issues and the car was pretty reliable. I traded it with over 100K after I needed a starter replacement. Fixed that and off to the dealership.
Excellent piece, Aaron. This is probably the most comprehensive and insightful examination of the V8-6-4 that I’ve read — I thoroughly enjoyed it.
While hindsight is 20/20, it does seem that Cadillac might have been better off continuing with the conventional 6.0L V8, accepting the gas guzzler tax, and avoiding modulated displacement altogether. The few Cadillac buyers concerned about fuel economy or the tax could have opted for the 4.1L V6 or even the diesel. However, the majority of Cadillac’s traditional clientele likely wouldn’t have been overly concerned about a relatively minor fuel economy penalty or tax.
I can’t say definitively whether keeping the 6.0L would have caused Cadillac to miss its CAFE targets in and incur penalties for 1981 and beyond, but it’s reasonable to wonder if that cost might have been less damaging in the long run than the reputational harm caused by the V8-6-4’s reliability issues.
Your contention that the HT4100 was not rushed into production is particularly interesting. The evidence you present suggests Cadillac never intended to continue the V8-6-4 into 1982, but timing seems crucial here. From what I’ve read, the HT4100 was originally meant to debut alongside the front-wheel-drive (FWD) C-body cars. Some accounts suggest those cars were planned for the 1983 model year but as we know they were delayed until 1985. This raises a question: when Cadillac sought the EPA exemption for the V8-6-4, did they already know the FWD C-bodies would be delayed past 1983? If so, was the decision to introduce the HT4100 before the new FWD platform a partially a direct consequence of that delay?
It seems clear the HT4100 was much better suited to the smaller, lighter FWD C-bodies. I find it hard to imagine anyone at Cadillac truly believed that engine could adequately power the large RWD C-body Cadillacs — and, as we learned, it couldn’t. Perhaps using the HT4100 in the 1982 cars was an act of desperation to meet EPA, CAFE and avoid the gas guzzler tax, or the best of several poor options.
It’s possible the original plan was to use the V8-6-4 as a stop-gap for the 1981–82 RWD C-bodies until the HT4100 and the FWD cars could launch together. But when the V8-6-4 failed to meet expectations, Cadillac may have been forced into a last-minute pivot — introducing the HT4100 early to avoid gas guzzler taxes. If that decision occurred before their EPA application for the exemption, it might explain why Cadillac didn’t request an exemption for the 1982 model year.
Alternatively, had Cadillac been more open to using corporate engines at the time, they might have saved themselves considerable trouble and money. Instead of investing time and money in the V8-6-4, they could have paired their Digital Fuel Injection (DFI) system with the Oldsmobile 307 and backed it with the TH200-4R transmission as an interim solution. Cadillac buyers had already accepted the Olds 350 in the Seville, so the smaller 307 might have worked as well. Then again, I doubt if there would have been sufficient Oldsmobile V8 production capacity. Ironically, Cadillac did adopt the 307 and TH200-4R in the RWD D-body cars by 1986, though it was saddled with the outdated E4ME electronic feedback Quadrajet. Even so, that combination turned out to be one of Cadillac’s best powertrains of the 1980s, achieving a solid balance of fuel economy, emissions compliance, and reliability.
In the end, the V8-6-4 fiasco serves as a good example of the poor decision making at GM during this era. Decades later, modern displacement-on-demand and dynamic fuel management systems still struggle with many of the same issues: minimal real-world fuel economy gains offset by added complexity and reliability concerns. My own daily driver is V8-powered, but I deliberately avoided any vehicle with DOD. The EPA ratings might look worse on paper, but in my experience — and through many comparable rental vehicles with DOD — the real-world difference is minimal.
Regarding the latter, I’d say no, not at all. The HT4100 was tied to the new Livonia engine plant, which was supposed to be a huge step forward for Cadillac in technology and labor (both in greater use of automation and in the Livonia plant’s unique labor approach, which has been much discussed elsewhere). Cadillac obviously saw all that as the wave of the future, and they had a lot riding on it.
Judging by the rumors circulating in 1979, they were actually hoping to get the new engine ready to use on at least some cars for the 1981 model year. The timing didn’t end up working out for that, but as soon as plant construction was complete, which it was by late spring/early summer of 1980, they began tooling for HT4100 production, which was up and running in July 1981. (It certainly would not have made any financial sense to let the new plant gather dust for a year or more while waiting for the next product changeover.)
From a design standpoint, I’m sure there was probably discussion early on about making the HT4100 suitable for FWD installation in the downsized C-bodies, but I didn’t see any indication that the HT4100 introduction was tied to the C-body launch. To the contrary, Cadillac seemed to have wanted the HT4100 engine as soon as they could get it.
They sold both the Buick 252 and the Olds diesel V-8, which had dismal acceleration, so if anyone was very concerned about that, they’d long since been overruled.
Because the HT4100 was tied to the new engine plant, this was really not just a product decision: It was a major capital investment that involved a major shift in Cadillac production and labor practices, with almost totally new equipment and tooling. It also involved the future of the V-8 at Cadillac. In the late ’70s, GM assumed that virtually all their mainstream V-8 engines were going to have to be phased out by 1985; as a design, the HT4100 was pretty clearly aimed at demonstrating that Cadillac could make a V-8 that would be as fuel-efficient as the Buick V-6 and thus justify retaining V-8 power.
As for Oldsmobile, production capacity would have been an issue. Through 1981, Pontiac had supplied a large number of 5-liter V-8s for Buick and Oldsmobile. For 1982, the Pontiac 301 was dropped so their plant capacity could be used for four-cylinder engines, so the Olds 307 and Chevrolet 305 had to pick up the slack. Cadillac needed a non-trivial number of engines (around 175K, based on actual 1982 production), and for financial reasons, they needed to make use of the plants and tooling available to them, since there were already enormous sunk costs.
In terms of investment and time, I’m not convinced that having to adapt the Olds 307 to their digital throttle body engine management system would have been meaningfully cheaper than the V8-6-4 — perhaps less, also taking into account the economics of getting engines from Oldsmobile and plant utilization issues.
I completely understand Cadillac’s design goals and the rationale behind the HT4100. I would contend that you’ve made a very strong argument that the HT4100 engine was not tied to the FWD C-body, as many histories indicate. That said, I can’t help but think that the HT4100’s use in the 1982 RWD C-body was something of a knee-jerk reaction to the V8-6-4’s failure to deliver on its promises. It makes little sense to offer this engine in an outgoing model—one that was already being phased out—except for the fact that the V8-6-4 utterly failed to achieve sufficient improvements in fuel economy and emissions.
Could it not have been possible that Cadillac originally intended to install the HT4100 only in its smaller and lighter Seville and Eldorado models when the engine was first launched and continue the V8-6-4 in the RWD C-body (had it been successful in meeting mpg and emissions goals). The Seville and Eldorado would have been far more suitable to showcase a new, more efficient V-8. This approach would also have allowed the Livonia plant to ramp up production gradually ahead of the FWD C-body’s release, while the Detroit plant could have wound down 368 production for the RWD C-body Fleetwood, which was seemingly scheduled for replacement in 1983 with the smaller HT4100 powered FWD C-body.
The history of GM during this period is fascinating, yet few primary sources have definitively explained the rationale behind many of the company’s decisions. Much of it still feels like educated speculation which is why I enjoy this dicussion. Clearly even Templin was spinning the facts back then, so who knows what facts have been lost in the sands of time.
As dismal as the 4.1L Buick V6’s acceleration was, the HT4100 was certainly no better (depending on gearing and transmission). Both were rated at 125 hp, but the V6 offered 15 lb-ft more torque than the HT4100’s 190 lb-ft. I don’t have road tests that directly compare the two, but Automobile-Catalog’s simulation program estimated that a 1982 DeVille with the 4.1L V6 was actually slightly quicker to 60 mph—13.9 seconds versus the HT4100’s 14.1 seconds. Other than improved NVH, the HT4100 really didn’t offer significant advantages over the Buick V6. To show how pathetic the HT4100 was, I did find a Motor Trend test of a 1980 Seville equipped with a 368 that ran 0-60 in 10.6 seconds, while Motor Trend’s test of a 1982 HT4100 powered Seville only managed a dismal 15.4 seconds to 60 mph.
In a perfect world, that might have worked. But as you pointed out—and I originally alluded to—the production capacity likely wasn’t there. By 1986, GM had surplus Oldsmobile V8 production, which I suspect is why all GM B-body wagons transitioned to the 307 partway through the 1986 model year, as did some Pontiac Parisienne sedans. A little-known fact: many Canadian-market Caprice sedans also used 307 V8s, likely to help absorb the production surplus. Since Canada had yet to update its emissions regulations to match the U.S. EPA standards, it was likely much easier to make this change in the Canadian Market. This is one of the few times a V8 other than a Chevrolet was used in a Chevrolet vehicle.
I strongly disagree, and that argument — which is made by a lot of Cadillac histories — is simply not supported by the contemporary evidence. Any concern about how the HT4100 fared in terms of performance was a stubby tail wagging a very large dog. Cadillac was aware of the gas tax thresholds (which were enacted in November 1978) and I’m sure they were acutely aware of their expected contributions to CAFE. They wanted and needed the HT4100 as soon as they could get it, and the only purposes of the V8-6-4 were to keep them out of gas guzzler tax territory in the meantime and (based on what they told the EPA) give them “field experience” with a technology they might use later on something else. All the important decisions were made before the V8-6-4 got into customer hands, and the V8-6-4 would probably have NOT kept them from being hit with a gas guzzler tax for 1982 even if it had worked fine otherwise.
Had the Livonia plant been ready sooner, I think they would have likely phased in the HT4100 during the 1981 model year, which early rumors suggested they would do. Would it have gone first into the Seville and Eldorado? Maybe, but if so, then probably based on production volume rather than weight or performance.
Introducing a new engine — an all-new engine in a new plant, in this case — involved substantial lead time for plant setup, tooling, and EPA certification. It’s not something that an automaker could just do in the spring for introduction in the fall, even if they wanted to.
Cadillac also did not have the luxury of just ignoring the RWD C-bodies until it was convenient. The existing De Ville and Fleetwood Brougham were not low-volume holdovers like the RWD Brougham later became. They were Cadillac’s volume models, still selling 175K a year in a terrible economy, which made the impact of their fuel economy particularly acute.
Perhaps I didn’t explain things clearly enough. My argument is not that the V8-6-4 was released to the public and, afterwards, due to its unreliability or poor performance, Cadillac replaced it with the HT4100 at the last moment. I agree—that’s what most histories state, but it’s not what happened. My thought is that during the testing phase, the engineering team realized the modulated displacement system would not be sufficient to meet the more stringent emissions and fuel economy standards beyond 1981. Heck, it seems they wanted a pass for 1981 too – clearly the design did not return the gains that they expected.
So, my theory is that because of its inability to meet the design team’s goals for fuel economy and emissions (not performance), they decided not to continue using the V8-6-4 after 1981 and substituted the HT4100 “as a last minute change.” Had this happened, and again I am am only theorizing, it likely would have occurred well before the 1981 MY cars were released to the public – and it likely would have had to have been prior to March 1980 when it made the EPA application. So, there would have been adequate time for EPA certification for the 1982 MY cars with the HT4100 had this been the “last minute change” to abandon the V8-6-4 after 1981. And maybe this is where the HT4100 rushed to production histories came from – as even falsehoods tend to have some truth to them. It seems logical that an investment of this size for the V8-6-4 would have initially been intended for use across more than one model year – but maybe GM was really that wasteful.
And of course I am aware of the volume of the RWD C-body prior to the 1985 FWD conversion. Which is why I mentioned I don’t know the impact on CAFE for Cadillac had it continued the 368 into 1981 without modulated displacement in my original comment – implying I knew it would have an significant impact had they continued on with the standard 368 into 1981.
According to the EPA:
Cadillac was concerned about the modulated displacement engine’s ability to pass durability on CO because of AF fluctuations during mode transition. The EPA pointed out that a) the test data indicated that it probably WOULD pass durability; b) Cadillac had not completed durability for the V8-6-4 at the 1980 7.0 CO standard either, so there was no lead time savings in doing that; and c) GM had completed durability with a non-M.D. DEFI 6.0, so they had an approved alternative, even if it would likely incur a gas guzzler tax. I don’t think that leaves much doubt that avoiding the gas guzzler tax in 1981 was Cadillac’s primary priority with this technology.
The investment in the modulated displacement technology was a drop in the bucket compared to the investment in the Livonia engine plant and HT4100 tooling. The advantage of the cylinder deactivation system was that it was something they could add to the existing engine to keep it out of gas guzzler territory without requiring any substantial tooling changes to an engine they were already preparing to phase out, and without switching to a new transmission. It did cost, I’m sure, and I don’t know what kind of licensing arrangement they had with Eaton for the underlying patents, but Cadillac had hundreds of millions of dollars riding on the Livonia plant and the HT4100.
Here’s the timeline: GM applied for the CO waiver in March 1980. They asked for only a one-year waiver for the 6.0 M.D. engine, for 1981, although they could have requested a two-year waiver — they did so for the 1.6-liter four, submitted a few weeks later, and they actually got it. At a public hearing on May 8, 1980, GM representatives testified that they were not aware of ANY GM production models that would use the modulated displacement system in 1982 or beyond. That was over two months BEFORE the EPA ruled on the waiver request, and Templin later claimed that they thought the EPA WOULD give them the waiver for 1981, so that doesn’t appear to have been a factor in those statements. By the end of 1980, GM had already announced the imminent shutdown of the Detroit Cadillac Engine plant (where the 368 was built) in favor of Livonia (see here), so barring some kind of major setback with the Livonia plant, they were already pretty well committed.
I should note that the HT4100 presented an additional advantage for fuel economy and emissions compliance for the RWD C-bodies: It was enough lighter than the 368 that I’m pretty sure it dropped the C-bodies, or most of them, down one inertia weight class.
(For those who aren’t familiar with older emissions certification procedures, the inertia weight was the resistance setting used on the chassis dynamometer to simulate “road load” during emissions testing. It was originally divided into classes of 250 and 500 lb, so being able to switch to a lower class meant less resistance, meaning the engine didn’t have to work as hard and didn’t burn as much fuel or produce as much emissions.)
Interesting, thanks for the extra detail Aaron. Undoubtedly the bigger picture was the huge investment in the Livonia plant, but I was speaking more about the decisions for the short term to get them over the hump. If as you contend, Cadillac only ever planned to use the V8-6-4 for one year, it does seem to be a bit wasteful – especially with the licensing costs to Eaton. Then again, this is GM of the 1980s we are discussing.
I also hadn’t considered the weight reduction, although the shipping weights did not decrease by 200 lbs as Cadillac implied with weight comparison between the two engines – it was less than 100 lb according to the shipping weights.
In your research, did you find out the program cost for the V8-6-4? I do wonder on how this cost would have compared to had they simply kept the standard 368 in production for 1981 and paid the penalties.
I’ve never seen any estimates of the program cost for the modular displacement system, but I don’t think it was terribly much. The attraction was an add-on for an existing engine; there were obviously development costs involved, but tooling is orders of magnitude more expensive than development, validation, and programming, and the tooling costs were clearly modest.
Assuming that Cadillac had used the non-M.D. 368 with DEFI for 1981, with the same EPA ratings as 1980 49-state cars, the gas guzzler tax on 1981 gas V-8 cars would have totaled about $12.7 million, plus the fun challenge for dealers of selling cars with a “Gas Guzzler” warning on the EPA sticker in a still terrible economy. For 1982, the total tax would have been a bit under $43.5 million, assuming identical sales to what they actually had, rising to $143.4 million in 1983 and $183.3 million in 1984.
The 209 lb weight savings was the difference in dry engine weight, not total vehicle weight. Inertia weight class was determined based on loaded weight (curb weight plus 300 lb), but dropping a class meant a reduction of between 4 and 9 percent in road horsepower setting on the chassis dyno. This of course had no actual effect on customer fuel economy or real-world emissions performance, but it made it easier to hit the regulatory targets.
Interesting—thank you for taking the time to calculate the costs. Returning to my original post, based on your estimates, perhaps retaining the non-modulated 368 into 1981 would have been the better long-term option. Those concerned about the gas guzzler tax already had alternatives, the 4.1L V6 or the 350 diesel, and by 1982, the HT4100 would have served as the longer-term (albeit still poor) solution.
Even if the modulated engine program cost less than $12 million, I’m sure some of those expenses could have been offset by a modest price increase for vehicles equipped with the 368. However, the potential savings from avoiding the reputational damage would have been far greater—something Cadillac may not have considered, or perhaps, in their arrogance, did not believe would matter. Undoubtely during the testing phase engineers would have known this modulated engine system was not that great – not only failing to meet MPG and emissions goals, but also quite poor in operation.
As for the weight savings, I understand all that and recognize that those figures represent the listed dry weights for each engine, which is why I specifically spoke of the vehicle shipping weights. I was simply pointing out that the actual weight difference between the 1981 and 1982 models was nowhere near the 209 lbs difference in dry engine weights. There should have also been some small weight savings in going from a TH400 to a TH2004R transmission as well. This suggests there may have been some additional weight associated with the new HT4100 engine or there was weight added elsewhere in the vehicle for 1982.
Kind of a corollary point on new model introduction schedules: The Oldsmobile 4.3-liter V-6 diesel, which was also a new engine built in an all-new plant (for which Olds broke ground in July 1979), was intended primarily for transverse installations in the FWD A-bodies and downsized C-body cars, but Olds also took the trouble to tool for a cheaper iron-head longitudinal version they could install in the RWD full-size cars and the remaining RWD intermediates (including the G-body Cutlass Supreme/Regal/Monte Carlo). At the time all that was planned, the RWD cars were intended to expire much earlier than they eventually did, but GM still anticipated needing more fuel efficient engines for them in the meantime.
Obviously, the diesel V-6 was a different program from a different division, but I think it’s revealing of GM’s strategic thinking in that period.
A little-known fact: many Canadian-market Caprice sedans also used 307 V8s, likely to help absorb the production surplus.
This strikes me as quite curious. GM Canada had their own engine (Chevy) production facilities, right? Why would they use the Olds 307 unless they were engine production constrained (in Canada)? They wouldn’t have done it as a “favor” to mop up Olds’ surplus capacity, it seems to me, at the expense of their own capacity. Unless they were production constrained, it seems there has to be more to that. But it’s not exactly a major issue in the larger picture.
At this time, all production of GM B-bodies had left Canada. Going by memory, I believe 1984 was the last year Oshawa built a B-body. Even the Pontiac Parisienne was built in the U.S. exclusively after 1984. As I’m sure you’re aware, by this time there was significant production consolidation across both sides of the border, and many Canadian-market cars were produced in the U.S., while many of the cars built in Canada went to the American market. I also believe GM of Canada was still producing Chevrolet V8 engines, but these went into other products, such as trucks, still being made in Canada.
That said, the Caprices sold in Canada with the 307 Oldsmobile V8 were all produced in U.S. plants, likely alongside the Chevrolet wagons, which also used the 307 Oldsmobile V8. While I don’t have the numbers to confirm this, it seems that every Canadian-market V8 equipped ’87 Caprice sedan I’ve seen over the years has the 307 rather than the 305. I believe Canadian emissions standards mirrored U.S. emissions around 1988, so for the 1988 model year, Canadian V8 Caprice sedans were once again equipped only with 305 Chevrolet engines.
Of course; that explains it. Thanks.
An engineer who lies is no engineer.
What does not make sense to me is why the intake and exhaust valves were closed during deactivation. Seems like the piston, still compressing would place an unnecessary force and decrease any fuel efficiency gains.
I thought a vent would be implemented to equalize the cylinder pressure.
But the compressed air in the cylinder then pushes the piston back down. This compression-release cycle causes only an extremely minor (almost imperceptible) loss in efficiency, if any at all. On the other hand, opening the intake valve would have created considerable vacuum pumping losses, and more losses in pushing out the air through the exhaust. It’s significantly more efficient to just compress the air and let it push the cylinder back down. Sounds perhaps counter-intuitive, but it takes a considerable amount of energy to move air through the valves and ports and manifolds.
Templin — whose word I would be inclined to take with a grain or two of salt, considering — claimed:
The valves had to stay closed because the throttle body injection system could not selectively cut off fuel to the cylinders. Allowing excess fuel to collect around the deactivated intake valves wasn’t great; allowing fuel into the cylinders that weren’t firing, where it could then recondense, was probably worse.
Still, you’ve hit on one of the limitations of cylinder deactivation, which is that the deactivated cylinders are still incurring frictional losses even though they aren’t producing any power.
I had the exact same thought as BPM. When in cyl mode, it’s a v4 driving a v4 pump, and one that’s blocked, at that! Almost impossible to believe that that is less work for the “active” v4 than air very freely rushing in and out of the inactive pump. I also always thought that pumping losses arose from the opening and shutting of the valves, and the back-up effect this has in the intake, or the pulsing effects in the exhaust.
I understand Aaron’s point about the TBi problem.
Excellent write up. I haven’t been able to drive my 78 Fleetwood enough to determine the fuel economy, but when I drove it home to Kingsport from Nashville, it returned a flat 16 on the highway.
On another note, Cindy’s aunt had an 81 Fleetwood with this awesome, I mean horrible engine. My FIL said that between the transmission shifting, the lock up torque converter and the engine moving around, it was miserable. My uncle and her were at the GM exhibition in Epcot and her uncle talked with a GM rep there. Cadillac agreed to disconnect the system but they would no longer have any warranty. When she went to trade it in a new 83 Cadillac, the dealer told her they wouldn’t take it in trade. She bought a Chrysler 5th Avenue !
Am I the only one who sees how crooked the right hand mirror control label is? Or the V8-6-4 emblem is? No wonder Acura and Lexus had no issue taking customers away from Cadillac
As to your last para, no, you are not! Car wasn’t just poorly engineered, it was sloppily assembled.
Thank you! I must say that I haven’t seen horrible build quality on my 78 Fleetwood, but I also haven’t done a deep inspection!
Sadly, I’m currently in a bad situation. The mechanic who took the car in to rebuild the carb, replace the timing chain, replace the intake manifold gasket and do the head gaskets has lost all interest. So I’ve been dealing with the owner of the property where my mechanic rents space. He assures me that he will have the car back together in two weeks. If not, I’m having it towed home-in pieces-and try to finish it myself. In 62 years, I’ve never had an issue like this. I guess trusting people is not a good idea
GM through the eighties is like watching a Greek tragedy. It was massive engineering or marketing failure after another, any one of which would have shut-down any other car company, with the worst being what they did to their highest profit division.
The only reason GM survived for another two decades (until the 2009 bankruptcy) is it took that long for them to eventually bleed off an entire generation of a once staunchly loyal customer base.
The 1980s were the decades from hell for GM and most especially Cadillac. They were just not prepared and equipped to deal with the rapidly changing market and regulations.
The HT should have arrived as a 4.5 L in the first place, at least for the RWD cars. It couldn’t have been that hard and it’s hard to imagine it incurring a meaningful mileage penalty.
I think the best strategy would have been to keep the 425 for the RWD cars but upgrade interiors, increase prices and reduce sales volumes so the CAFE impact was less. And then not to rush the 4100 and C body to market.
The FWD C body was actually delayed by a year and a half; it was originally scheduled for 1983.
This is an interesting take on a failed GM program. What gets me is the letter on display. Coming from a service advisor, we were always the ones who saw a problem first. When we informed the district manager of this, GM’s first line of defence was to deny the problem existed.
Of course the customer knew there was something wrong with their car. It was always a terrible experience to have to tell a customer “There is nothing wrong with your car” or “We’ll monitor the problem and see what happens.
Now GM is having problems with their 5.3 and 6.2 engines. They just never change.
Hehe. We can do that here too. The first line of defense is denial of the problem. And then comes the claim that the way things are, it’s just “state of the art.” In particular VW likes to use this approach in its home country, too.
Cadillac dealers were actually up in arms about the quality of these cars overall: They were unhappy about the fuel injection and modular displacement systems, but they had a whole array of complaints about poor build quality, breaking armrests, bad paint, etc., which they felt was really hurting their business. Cadillac’s response seems to have been dismissive.
Most of the financial problems GM has ever had can be traced back to corporate arrogance.
You should see what they are like to work for. I worked as a GM service advisor in 2006. At the time, GM was teetering on the edge of bankruptcy.
Instead of having a good product to sell, GM’s response was to berate dealers and sales people. In GM’s world, product did matter much. Sales skills were the be all and end all.
We all know how well that worked out.
This reminds me of an 89 Mercury Tracer we were leasing. I’ve written about it, but the transaxle was slipping something fierce. I cannot recall but it seems like the highway speed rpm’s was over 4000 at 55mph. I had to get a Ford district rep involved. We made an appointment and he left me sitting for about an hour. When we did meet, I was carrying a briefcase full of repair attempts. He asked my thoughts, and I offered for them to simply take the car back two years early-no money. I reminded him that
1) this model was now discontinued
2) it was built in Mexico
3) that Ford had already replaced an entire transaxle on my FIL’s Sable at a huge cost to Ford
And finally, that I had enough to take them through the Lemon Law-something I knew they didn’t want.
He drove the car, came back, asked the shop foreman if he’d ever looked at the car and noticed issues (which he had and had tried repeatedly to fix it) who lied and said “he’d never noticed any issues.
We ended up going to Mazda, and I told the salesman at my Mercury dealer that he could
A) take the car back with a $500 early termination fee (they wanted 12 months of payments)
or I’d bring the car back “in pieces” and that no judge would side with a big corporation with the some 40 pages of repair attempts.
They took the car back and that was the last new Mercury I ever owned.
It was mentioned that the 368 was used in some cars until 1983/84… what models were those? Or did I mis-read?
A guy my friend Phil in Quebec knows used to buy ’81 Caddies and would fix or turn off the cylinder deactivation, he had good luck with them somehow.
The Fleetwood Limousine (formerly known as the Series 75) retained the V8-6-4, the commercial chassis had the carbureted 368, both through 1984.
Apparently they were still offered in the 1983 and 1984 extended wheelbase Fleetwood 75 Limousines.
You’re right, Aaron. Cadillac stopped using the 60 and 75 designations after the 1976 model year.
“but it quickly became clear that the system had come out of the oven way too soon.”
There are still reliability and excessive wear issues on modern cylinder deactivation engines. Mechanics post about the problems all the time. Dumb idea back then, dumb idea now.
I know, the answer is cost, cost, cost, but did they ever consider putting on a modern, for the time, fuel injection system. Say Bosch L jet with Lambda? I know, it was the NIH problem, “Not Invented Here” But it was a Cadillac, which was still pretending to be the “Standard of the World” or some such thing. 140/265 HP/TQ out of a 368? That’s gotta be a typo. 240/365 maybe? That’s not exactly a high performance engine either. Multiple sources say it’s not so I guess not. I suspect GM still had enough engineering to reverse engineer the Bosch system to avoid patent problems if they were that dead set against paying royalties, but how much would it have really cost? I mean Caddy was supposed to be a premier brand, maybe it should have been priced like it?
I’m still convinced American manufactures decided in the late 60s, over emissions and safety that they would build the cars to spec, but people wouldn’t like them. But too bad. This is what we build, this is what you get, too bad. We can see where that got them.
Cadillac had port injection (albeit analog, not digital) with the earlier Bendix system, but they thought it was too expensive — it needed eight pricey injectors per engine, whereas throttle body injection used only two, and they had much lower operating pressure (about 10 psi versus 39 psi), so they were less expensive. That was why Templin was claiming throttle body injection was the greatest thing since canned beer. For the early ’80s, the system was pretty sophisticated, it just didn’t provide any great performance benefit, and they were trying to squeeze better mileage and lower emissions out of an engine that had originally been designed to be over 100 cubic inches larger than it ended up.
It’s almost impossible to conceive of the managerial incompetence that could have such a giant, profitable corporation producing such rubbish (and then lying about it). If we put aside the issues of arrogance, and the infamous American myopia about that place called Anywhere Else, was the central cause of GM’s failure upon failure over such a long period that they stuck like lemmings to their long-established formula of profit-per-unit (which I seem to recall was something absurd like 40% or something)? Surely ALL of these economy/emissions issues leading this quarter-assed cylinder cut-off nonsense would have been fixed with proper money thrown at R&D, and things like proper injection systems and Lambda sensors, especially on a pricey Caddy. Instead, it seems they preferred to spend time fighting the EPA and dragging their heels and selling crap.
I must emphasize that the V8-6-4 DEFI system DID have O2 sensor feedback control, as did the HT4100 system.