Science Fair Project Encyclopedia
GM LT engine
The second-generation Chevrolet Small-Block engine, which uses the LT prefix, was introduced in 1992. A special DOHC engine, the LT5, also used this prefix. The LT family was replaced with the all-aluminum GM LS engine family in the 2000s.
All LT engines displace 5.7 liters and have cast-iron blocks with aluminum or cast iron heads.
See the GM Small-Block engine page for information on the first generation of the 350 V8.
The 1990 LT5 was a special engine indeed. It was a 350 in³ (5.7 L) small-block V8, but was entirely different than the standard 350. 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 built by specialty engine builder, Mercury Marine. This engine produced 375 hp (280 kW) and 370 lb.ft (502 Nm) for the 1990-1994 Corvette ZR-1 and jumped to 405 hp (302 kW) and 385 lb.ft (522 Nm) for its final year, 1995 thanks to a better intake manifold. The engine was not used in any other vehicle.
The Generation II small block debuted in 1992 on the 1992 Chevrolet Corvette. Few parts from the G2 engine are interchangeable with the old G1 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.
In 1992, GM created a new-generation small-block engine and again called it LT1 to recall the 1970 LT1. 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.
A high-performance version of the 1996 LT1 was called LT4 for use in all manual transmission 1996 Corvettes including the Corvette Grand Sport . In the Camaro, the LT1 engine produced 275 hp (205 kW) and 325 lb.ft (441 Nm), with the Corvette and Ram-Air Firebird getting an even 300 hp (224 kW). The Camaro was up to 285 hp (227 kW) and 335 lb.ft (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 lb.ft (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. 1996 saw major revisions for OBD-II - a second catalytic converter on the F-body cars(which was standard since 1993 in the strict emissions laws of California), a crank position sensor, and of course the new OBD computer. The 1997 model year Camaro was the last year for this engine in a GM production car.
This engine was used in:
- Aluminum heads and 4-bolt mains
- Aluminum heads and 2-bolt mains
- Iron heads and 2-bolt mains, 4.3 (L99) and 5.7 liter options
The LT4 was a special high-performance version of the new-generation LT1. It was introduced in the 1996 model year, for the last year of the C4 Corvette. The engine was passed down to the Camaro and Firebird the next model year. With the addition of new higher-lift cam and port-matched intake runners, it produced 330 hp (246 kW) and 340 ft.lbf. (461 Nm) of torque. The LT4 was almost identical(in terms of power) to the all-aluminum LS1 of the C5 Corvette.
The LT4 was available on the following vehicles:
- 1996 Chevrolet Corvette Grand Sport, Collectors Edition, 6-speed
- 1997 Chevrolet Camaro SLP/LT4 SS 6-speed
- 1997 Pontiac Firebird SLP/LT4 Firehawk 6-speed
A 4.3 L version of the LT1 was introduced in 1994 for the Chevrolet Caprice. The bore was reduced to 102 mm and the stroke to 76 mm. Like the LT1, it features sequential fuel injection, reverse cooling , and an optical crank position sensor. Output is 200 hp and 245 ft.lbf.
See the GM LS engine page for more information on the newest small-block V8s.
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