Cadillac High Technology engine

A new lighter V8 engine was rushed into production for 1982, the HT-4100 (option code LT8). It was a 4100 cc V8, designed for rear-wheel drive and longitudinal front-wheel drive applications sharing the same transmission bellhousing pattern as Buick, Oldsmobile, and Pontiac engine equipped rear wheel drive vehicles. A new line of downsized Cadillacs with the transverse mounted V8 engine and front wheel-drive was slated for launch in 1983, however, delays in the downsizing program shared with Buick and Oldsmobile postponed their debut until mid 1984 when they were introduced as early 1985 models and shared what is known as the "Metric" bellhousing pattern.

HT stood for High Technology. For its time, the engine and its electronic control module (ECM) were quite sophisticated, despite having a throttle-body fuel injection system (as opposed to more advanced multiport fuel injection). Like the 6.0/368" DFI engines before it, the HT4100 used an ECM that incorporated a detailed on-board computer. Every parameter of engine performance could be displayed on the electronic climate control panel while the car was being driven. The HT4100 also adopted other modern design features including replaceable cylinder sleeves, high operating temperature for emission control (210 degrees, compared to 180 in earlier engines), free circulation of coolant between the block and the heads, and bimetal construction that mounted heat-tolerant cast-iron heads onto a weight-saving aluminum block. The engine had a bore and stroke of 88 mm × 84 mm (3.465 in × 3.307 in), for a total displacement of 4.1 L; 249.4 cu in (4,087 cc). It produced 135 hp (101 kW) at 4400 rpm and 190 lb⋅ft (258 N⋅m) of torque at 2000 rpm.

In 1982, the HT4100 debuted as the standard engine for all Cadillac models except the new compact Cimarron, and the Fleetwood limousines, which continued to carry the variable-displacement V8-6-4 engine until 1984.

The HT4100 was prone to failure of the intake manifold gasket due to scrubbing of the bi-metal interface, aluminum oil pump failure, cam bearing displacement, weak aluminum block castings and bolts pulling the aluminum threads from the block. It may not have been the most successful engine to sit under the hood of a Cadillac, but potential buyers were no more satisfied with the other two engines available at the time, the V8-6-4 and the Oldsmobile 5.7 L Diesel. Reliability issues soiled the reputation of the HT4100. As a result, the Oldsmobile V8 gas engines were a popular and straightforward conversion. Despite problems with the engines, Cadillac still had annual sales in the United States above 300,000 as late as 1986.^[3]

In 1987, a unique, more powerful engine was introduced in the Cadillac Allanté based on the same architecture. The Allanté 4.1 had a new, reinforced engine block that would later be used in the Cadillac 4.5, it used a different camshaft profile and roller lifters to provide for improved airflow, in addition to multiport fuel injection. This engine was rated at 170 hp (127 kW) at 4300 rpm and 235 lb⋅ft (319 N⋅m) of torque at 3200 rpm. Other than the basic architecture, the only thing the Allanté 4.1 shared with the HT4100 was the displacement, something easily changed in the engine family by simply using different diameter cast-iron cylinder liners.

The 4.1 standard HT 4100 was superseded by improved larger-displacement engines such as the 4.5 and 4.9, and the HT4100 ceased production after the 1987 model year.

• 1982–1985 Cadillac Fleetwood Brougham
• 1982–1987 Cadillac DeVille
• 1982–1987 Cadillac Eldorado
• 1982–1987 Cadillac Seville
• 1985–1987 Cadillac Fleetwood

• 1987–1988 Cadillac Allante has the same 4.1 liter displacement, but the block was unique and significantly reinforced, with many significant differences, making it a different engine, more closely related to the 1988-1989 4.5 liter Cadillac engine