General Motors High Tech Engine and Other CAFE Weaknesses (Part II)

In our latest edition of Discontinued History, we covered the years leading up to the release of the Cadillac High Technology V8. Used almost exclusively in 1981, the disastrous V8-6-4 had a primitive engine management system that could disable two or four cylinders on Cadillac’s traditional V8. And while the idea was good, the technology and engineering behind it was not. Cadillac was left in a bind and needed a replacement engine immediately. But the engine of choice was not finished and not ready for prime time. Ladies and gentlemen, welcome to the HT4100 mid-rare.

As last mentioned, the HT was supposed to debut on front-drive Cadillacs in 1983. However, after the V8-6-4 was a flop, the HT was applied to the brand’s existing lineup in 1982. This meant the HT was pushed through its latest development. stages at a breakneck pace and put into production much earlier than anticipated by The General.

Coded as the LT8, the new high-tech engine was considerably smaller and lighter than the 368 cu in (6.0 L) V8 it replaced. Known by its metric displacement, the 4.1 was not known by its 249 cubic inches. This old-school metric was heading well into the sunset of the early eighties. The HT could be applied to either rear- or front-wheel-drive Cadillacs. For marketing and luxury reasons, the HT engine was exclusive to Cadillac vehicles. Non-Cadillacs had to settle for less technologically prestigious engines.

One thing the Cadillac HT V8s shared with GM’s other offerings was the transmission bell housing, which was the same pattern found on front- and rear-wheel-drive Pontiac, Buick, and Oldsmobile passenger cars. This was particularly relevant for parts-sharing purposes, and the next front-drive Cadillac models were due to debut in 1983. But since the HT was put into production early, conversely, front-drive Cadillacs and their siblings were delayed. The downsizing project at GM ran into constant trouble, as everyone worked on an incorrect analysis that indicated fuel prices would skyrocket by 1985.

Front-drive Cadillacs were ready for the 1985 model year, much to almost everyone’s chagrin. Cadillacs equipped with the HT4100 were too small, too ugly, less attractive with front-wheel drive, and still too small. Lincoln hampered GM’s downsizing with its proud full-size cars that always came with length. The predicted spike in fuel prices did not materialize, and customers from Cadillac, Oldsmobile and Buick instead turned to larger luxury rivals. General Motors spent the next seven model years fixing its downsized front-wheel-drive Cadillacs. Around that time, the Northstar arrived (uh oh) and its traditional customer stopped driving altogether. But that’s a story for another day. Back to HT.

In 1982, Cadillac implemented its new engine across the entire line except for the all-new Cavalier-based Cimarron (where it wouldn’t fit) and the factory Fleetwood limo, which retained the 368 V8 until came to an end in 1984. Customers of the DeVille, Seville, Eldorado and Fleetwood Brougham found a lot more empty space in their engine bays if they had looked around. Where it applied, the 4.1 HT was standard equipment, while a 4.1-liter V6 was a credit option, and the diesel V8 cost extra. Later entries in the HT party included the new 1985 front-wheel-drive C-body Fleetwood and the 1987 Allante halo convertible.

The modern electronic control module that GM invented on the V8-6-4 was refined and became an important part of the new HT engine. It still operated the same as in the 368 V8 and monitored engine performance via an on-board diagnostic system. As before, information from the ECU was displayed directly on the climate control panel, while the car was driving. No attempt was made to program cylinder deactivation. Elsewhere, General Motors played it a bit more traditional and opted for throttle-body fuel injection instead of multiport. The 4.1 managed 135 modern horsepower and 190 lb-ft of torque.

The TBI was joined by a higher operating temperature, which meant the engine burned cleaner and had better emissions. Other modern engine advancements include mixed metal construction: durable cast iron heads were attached to a lighter aluminum block. The cylinder liners were replaceable. Vital coolant circulated freely between the engine block and the heads, rushing along the various rugged surfaces of the engine’s interior.

The problems appeared almost immediately. The problems started with the block itself, as the HT4100 experienced faults quite similar to its Northstar successor a decade later: the bolts came off the aluminum block and took the wires with them. That wasn’t the only concern with the block itself. It seemed that the HT’s rushed production schedule was resulting in quality control issues, such as weak engine block castings.

Outside of the block, the HT4100 often experienced intake manifold gasket failure when two dissimilar metals rubbed against each other. Aluminum was also used in other high stress areas. The oil pump of the HT4100 was made of it and often failed. Camshaft bearings also failed and fell into oblivion.

Customers weren’t happy with the HT4100 given all of its issues, but the engine was always an improvement over the V8-6-4 that swelled in their 1981 Cadillacs. It was also much better than the simply terrible 5.7-liter Diesel offered through Oldsmobile. The HT4100 acquired a bad reputation almost instantly for all the reasons cited above, even though Cadillac was still selling a large number of cars at the time. In 1981, 230,665 people bought Cadillacs, most of which were equipped with the V8-6-4. This infamous engine was well known as customers returned in 1982 and boosted Cadillac sales to 249,295. Sales also increased under the HT4100 tenure, reaching just over 300,000 in 1983 and 320,027 in 1984. Buyers were loyal and simply had to have that Cadillac style.

Final development of the HT4100 came in 1987, when the engine was finally added to the long-awaited, disastrous and very expensive Allante. For $54,000 (adj. $135,389) from a customer in 1987, they received a very special version of the 4.1-liter in their front-wheel-drive, Pininfarina-designed convertible. Inside the engine, a revised camshaft profile and hydraulic roller lifters were used. Both revisions helped improve airflow and increase the horsepower of the 4.1 significantly on the standard engine. Power was up to 170 horsepower (up from 135) and torque was 235 lb-ft. This version of the HT was exclusive to Allante and produced for only two years.

Before we go any further with the HT, we need to take a quick sidebar in a GM engine spawned entirely by emissions regulations: the Oldsmobile diesel. Through his various versions, he was still bad but didn’t have to be. Its problems stemmed from a rushed development schedule and continued cost-cutting by GM’s accountants. Until next time.

[Images: GM]

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