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CATEGORIES (articles) > Engines > Chevy Engines > Chevy LT series V8 engine

Chevy LT series V8 engine


The second-generation Chevrolet Small-Block engine, which uses the LT prefix, was introduced in 1992. The distinguishing feature of this engine family was the use of reverse-flow cooling, which enabled higher compression ratios than previous versions of the small-block Chevy.

A special DOHC engine, the LT5, also used this prefix.

The LT family was replaced with the all-aluminum GM LS engine family in 1997 (in the Chevrolet Corvette), and 1998 (in the Chevrolet Camaro and the Pontiac Firebird Trans Am and Forumla models).


Generation I

See the GM Small-Block engine page for information on the first generation of the 350 V8.

LT5

A GM LT5 engine

Immediately prior to the release of the second generation Small-Block, General Motors released a largely unrelated engine which also used the LT name. The LT5 was a special engine indeed. It was an all-aluminum 349 in³ (5.7 L) small-block V8, but was entirely 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 a Lotus-designed 32-valve DOHC head. It was hand built by specialty engine builder, Mercury Marine. This engine produced 375 hp (280 kW) and 370 ft·lbf (502 Nm) for the 1990-1992 Corvette ZR-1 and jumped to 405 hp (302 kW) and 385 ft·lbf (522 Nm) 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 not used in any other vehicle.

Generation II

The Generation II small block debuted in 1992 on the 1992 Chevrolet Corvette. Few parts from the Generation II engine are interchangeable with the old generation I engine. It uses a new engine block, cylinder head, timing cover, water pump, intake manifold and accessory brackets. On the other hand, the engine mounts and bellhousing bolt pattern remain the same, so the new engine is easier to swap into an older car than another model V8 would be. One visible difference is the new "opti-spark" distributor which is located on the front of the engine behind the gear-driven water pump.

A key technical difference between the original 350 and the Generation II small block is the cooling system. The engine employs reverse cooling, meaning that the coolant starts at the heads and then flows down through the block. This allows for a higher compression ratio and more spark advance since the heads are kept at a cooler temperature. A secondary benefit of reverse cooling is that cylinder temperatures are higher and more consistant.

LT1

In 1992, GM created a new-generation small-block engine and again called it LT1 to recall the 1970 LT-1. It displaced 5.7 liters and was a 2-valve pushrod design, although a 4.3 liter variant known as the L99 was also offered beginning in 1994. The LT1 was unique with a reverse-flow cooling system which allowed for the engine to run at a higher compression. This was accomplished by cooling the heads first, thus reducing the risk for engine knock at the higher compression.

Other cars received detuned versions of the LT1 in the years following 1992. In the Camaro and Firebird, the LT1 engine produced 275 hp (205 kW) and 325 ft·lbf (441 Nm), with the Corvette and Ram-Air Firebird getting 305 hp (227 kW). The Camaro was up to 285 hp (227 kW) and 335 ft·lbf (454 Nm) with this engine in the 1996 model year with the addition of dual catalytic converters. In the 1994 to 1996 B-body (Impala SS, Caprice and Roadmaster) and D-body (Fleetwood) version, the LT1 engine produced 260 hp (194 kW) and 330 ft·lbf (447Nm).

There were a few different versions of the LT1. All feature a cast iron block, but only the Corvette and F-bodies got aluminum heads. 1994 saw new sequential port injection and a mass airflow sensor. A new vented version of the opti-spark distributor appeared in 1994 on the B-Bodies and Fleetwood and in 1995 on the Corvette and F-Bodies. 1996 saw major revisions for OBD-II - a second catalytic converter on the F-body cars(which was standard since 1993 in California), a crank position sensor, rear oxygen sensors, and a new computer. Some OBD-II features had been added to the Corvette starting in 1994 for testing purposes. The 1997 model year Camaro and Firebird were the last year for this engine in a GM production car.

This engine was used in:

  • Aluminum heads and 4-bolt mains
    • 1992-1996 Chevrolet Corvette C4
  • Aluminum heads and 2-bolt mains
    • 1993-1997 Chevrolet Camaro Z28/Pontiac Firebird Formula and Trans Am variants
  • Iron heads and 2-bolt mains, 4.3 (L99) and 5.7 liter options
    • 1994-1996 Buick Roadmaster (LT1 only)
    • 1994-1996 Cadillac Fleetwood (LT1 only)
    • 1994-1996 Chevrolet Caprice (LT1 or L99)
    • 1994-1996 Chevrolet Caprice Police Package (LT1 or L99)
    • 1994-1996 Chevrolet Impala SS (LT1 only)

LT4

The LT4 was a special high-performance version of the new-generation LT1. With the addition of new higher-lift rocker arms and better-flowing heads, it produced 330 hp (246 kW) and 340 ft.lbf. (461 Nm) of torque. It was introduced in the 1996 model year, for the last year of the C4 Corvette, and came standard on all manual transmission (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:

  • 1996 Chevrolet Corvette when equipped with 6-speed manual transmission (includes all Grand Sports) (Production: 6,359)
  • 1997 Chevrolet Camaro SLP/LT4 SS 6-speed (Production: 100)
  • 1997 Pontiac Firebird SLP/LT4 Firehawk 6-speed (Production: 29)

L99 (4.3L)

A 4.3 L version of the LT1, designated the L99, was introduced in 1994 for the Chevrolet Caprice. It was externally identical to the LT1, but the bore was reduced to 3.736" and the stroke to 3.00" (similar to the late sixties Chevrolet 302 used in the first-generation Camaro Z28s). The pistons used in the L99 were the same as the ones used in the Vortec 5000 with the use of 5.94" connecting rods.

Like the LT1, it features sequential fuel injection, reverse cooling, and an optical crank position sensor. Output is 200 hp and 245 ft.lbf.

Due to its smaller displacement, it provides better fuel economy over the 5.7L LT1.




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