GM LT engine

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The LT6 and LT7 are not part of the LT V8 family. See Oldsmobile Diesel V6 engine.

General Motors' Generation II LT is a small block V8 engine. Making its debut in the 1992 Chevrolet Corvette, the new LT sought to draw upon the heritage of the 1970 Chevrolet LT-1.

A significant improvement over the original Generation I V8 is the Generation II LT's "reverse cooling" system, allowing coolant to start at the heads and flow down through the block. This keeps the heads cooler, affording greater power through a higher compression ratio and greater spark advance at the same time it maintains higher and more consistent cylinder temperatures.

Some parts from the Generation II are interchangeable with the Generation I one-piece rear main seal engine. The interchangeable parts include the rotating assembly (crank shaft, pistons, connecting rods, and flywheel/flexplate) and valvetrain assembly (not including timing set, which includes a gear to drive the water pump). The LT uses a new engine block, cylinder head, timing cover, water pump, intake manifold and accessory brackets. The harmonic dampener also does not interchange; it is a unique dampener/pulley assembly. Engine mounts and bell housing bolt pattern remain the same, permitting a newer engine to be readily swapped into an older vehicle.

Contents

101.6 mm (4.00 in) bore blocks

LT1

GM LT1 from a 1993 Chevrolet Camaro Z28.

In 1992, GM created a new-generation small-block engine called the "LT1 350", not to be confused with the high-output Generation I LT-1 of the 1970s. It displaced 5.7 L (350 cu in), hence the name "350" and was a 2-valve pushrod design. The LT1 used a reverse-flow cooling system which cooled the cylinder heads first, maintaining lower cylinder temperatures and allowing the engine to run at a higher compression than its immediate predecessors. An all new LT-1 engine has been announced for the 2014 Corvette based on the current LS engine family. This new variant of the LT-1 will be the new LS gen 5 engine platform. While retaining the familiar LS family architecture nearly every part has been extensively redesigned including the new direct fuel injection heads. Early estimates of the official horsepower ratings stand at 450.

This engine was used in:

There were a few different versions of the LT1. All feature a cast iron block, with aluminum heads in the Y and F bodies, and cast iron heads in the B and D bodies. Corvette blocks had four-bolt main caps, while most other blocks were two-bolt main caps.

The 92–93 LT1s used speed density fuel management, batch-fire fuel injection and a dedicated engine control module (ECM). In 94 the LT1 switched to a mass airflow sensor and sequential port injection. A new, more capable computer controlled the transmission as well as the engine and got a new name: powertrain control module (PCM). Where the ECM held its calibration information in a replaceable chip, the PCM was reprogrammable through the diagnostic port.

The early Optispark distributor had durability problems and a revised version was introduced with vacuum vents to remove moisture on the 1994 B-Bodies and in 1995 on the Y and F-Bodies; the vacuum vents can be added onto earlier distributors.[1] 1996 saw major revisions for OBD-II: a second catalytic converter on the F-body cars and rear oxygen sensors to monitor catalyst efficiency. Some OBD-II features had been added to the Corvette starting in 1994 for testing purposes.[citation needed] The 1997 model year Camaro and Firebird were the last year for this engine in a GM production car before it was replaced by the LS1, which was already in the Corvette for 1997.

The 1992 LT1 in the Y-body was factory rated at 300 hp (220 kW) and 330 lb·ft (447 N·m). 96 LT1 Y-bodies were rated at 300 hp (220 kW) and 340 lb·ft (461 N·m). The 93–95 F-bodies were rated at 275 horsepower (205 kW) and 325 lb·ft (441 N·m), while the 96–97 cars were rated at 285 horsepower (213 kW) and 335 lb·ft (454 N·m). The 96–97 WS6 and SS F-bodies were rated at 305 hp (227 kW). The 94–96 B and D-body version was rated at 260 horsepower (190 kW) and 330 lb·ft (447 N·m).

LT4

The LT4 was a special high-performance version of the new-generation LT1. With the addition of a slightly more aggressive camshaft profile, 1.6:1 roller aluminum rocker arms, high-flow cylinder heads, and an intake manifold (painted red) with extra material above the port available to allow port matching to the raised port LT4 cylinder heads, it was rated at 330 horsepower (250 kW) and 340 lb·ft (461 N·m). It was introduced in the 1996 model year, for the last year of the C4 Corvette, and came standard on all manual transmission (ZF 6-speed equipped) C4 Corvettes. The engine was passed down to special versions of the Camaro and Firebird the next model year.

The LT4 was available on the following vehicles:

All 135 production engines for the Firehawks and Camaro SS were completely disassembled, balanced, blueprinted and honed with stress plates. One in 5 engines was tested on a Superflow engine dyno and every car was tested on a chassis dyno in addition to performing a short 6-mile (10 km) road test. \

94.9 mm (3.736 in) bore blocks

L99 (4.3L)

A 260 in3 (4.3 L) was based on a 305 in3 with updated block architecture to be Generation II and a reduced 3 inches (76 mm) stroke. It was designated the L99, and was introduced in 1994 for the Chevrolet Caprice. It was externally identical to the LT1, but the bore was decreased to 3.736 inches (94.9 mm) and the stroke to 3 inches (76 mm) giving it a displacement of 263 in3. The pistons used in the L99 were the same as the ones used in the Vortec 5000, but 5.94 inches (151 mm) connecting rods were used to compensate for the shorter stroke. This was the base engine used on all 1994-1996 Chevrolet Caprice Sedans, including the Police Package vehicles.

Like the LT1, it features sequential fuel injection, reverse-flow cooling, and an optical ignition pickup. Output is 200 hp (150 kW) and 245 lb·ft (332 N·m). Due to its smaller displacement, it provides better fuel economy than the 5.7 L LT1, but at reduced horsepower & torque levels.

LT5

A GM LT5 engine

For model year 1990, Chevrolet released the Corvette ZR-1 with the radical overhead cam LT5 engine, which shared only the 4.4 inch bore spacing with any previous LT engine. The LT5 was engineered by Lotus Engineering in the UK headed by design manager David Whitehead, the engine was produced by Mercury Marine at Stillwater OK headed by Project Engineer Terry D. Stinson.[2] It was an all-aluminum 5.7 L (349 cu in) small-block V8, but was thoroughly different from any of the other Chevrolet 350 engines. The bore and stroke were both different at 3.9 by 3.66 in (99 by 93 mm) instead of the usual 4 by 3.48 in (102 by 88 mm) and it featured Lotus-designed 32-valve DOHC heads rather than the usual Chevrolet 16-Valve OHV Heads. It was hand built by specialty engine builder, Mercury Marine in Stillwater, OK. This engine produced 375 horsepower (280 kW) and 370 lb·ft (502 N·m) for the 1990-1992 Corvette ZR-1 and jumped to 405 horsepower (302 kW) and 385 lb·ft (522 N·m) for 1993 to its final year in 1995, thanks to cam timing changes and improvements to the engine porting. 1993 also added 4-bolt main bearing caps and an exhaust gas recirculation system. The engine was used only in Corvettes.[3] The LT5 was very expensive, and after six years of production, GM canceled the ZR-1 option. A total of 6939 were produced.[4] The LT5 however wasn't an evolutionary dead end. Despite being discontinued, a new class of premium V8s for Cadillac and eventually Oldsmobile, the dual overhead cam V8 Northstar and its derivatives, drew heavily from the LT5's design and lessons learned from its production.[5]

The LT5 does not have reverse cooling.

The LT5 was available on the following vehicles:

See also

References