The identification of a GM engine is commonly referred to by its RPO code. A Regular Production Option (RPO) is made up of three lphanumeric characters to uniquely identify a vehicle option. In 1985, General Motors introduced the 5.7L multiport injection engine as RPO “L98.” However, while the RPO “LS1” is specific to the 5.7L engine in the 1997–2003 Corvette and 1998–2002 Camaro and Firebird, there are variations among these engines. Throttle type (cable or electronic), intake manifold, and oil pan are only a few examples of different equipment on these engines. The content of this book is relevant for the most popular GM V-8 fuel-injected engines; the L98, LT1, LS1, and LS-series truck engines.
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The identification of a GM engine is commonly referred to by its RPO code. A Regular Production Option (RPO) is made up of three lphanumeric characters to uniquely identify a vehicle option. In 1985, General Motors introduced the 5.7L multiport injection engine as RPO “L98.” However, while the RPO “LS1” is specific to the 5.7L engine in the 1997–2003 Corvette and 1998–2002 Camaro and Firebird, there are variations among these engines. Throttle type (cable or electronic), intake manifold, and oil pan are only a few examples of different equipment on these engines. The content of this book is relevant for the most popular GM V-8 fuel-injected engines; the L98, LT1, LS1, and LS-series truck engines.
Generation I, with Multi-Port Fuel Injection
The first GM 5.7L V-8 engine with electronic multi-port fuel injection was introduced with the 1985 Corvette as RPO L98. A smaller, 5.0L V-8 engine with electronic multi-port fuel injection was introduced with the 1985 Camaro and Firebird as RPO LB9. Both engines are commonly referred to as tuned port injection (TPI) because of the shared, longtube runner, intake manifold design. With the exception of the distributor assembly, mass airflow sensor, and knock sensor, the sensors on these engines are fully compatible with Gen III PCMs.
The 1985 L98 engine was a hit among modern enthusiasts. These TPI engines were a big leap forward in fuel management technology and remain popular today.
The next 5.7L and 5.0L multiport fuel-injected engines were installed in many 1996–2000 lightduty Chevrolet/GMC trucks, SUVs, and full-size vans. The Express Van continued to use these engines through 2002. The 1996–2002 5.7L and 5.0L engines are also known as Vortec 5700 (RPO L31) and Vortec 5000 (RPO L30), respectively. The fuel injector arrangement inside the intake manifold has made these engines undesirable for conversions. The unique Vortec engine intake manifold bolt arrangement and raised intake runners on the cylinder heads limit intake manifold selection. A cast-iron marine engine manifold, however, with conventional injector and fuel rail configuration makes for a desirable upgrade. Most sensors on these Vortec engines are compatible with Gen III PCMs.
Generation II, 1992–1997 LT1 and 1996–1997 LT4
General Motors changed the traditional V-8 cooling system and ignition system with the 1992 Corvette with the 5.7L LT1 engine. The higher horsepower LT4 engine was an option beginning in 1996. Compared to the L98 engine, minor changes were made to the sensors for fitment on these new engines. Functionally, many of the sensors remained the same. The ignition system is unique in that the engine control module (ECM) uses low- and high resolution pulse counts from the distributor to determine engine position and ignition events. With the exception of this new distributor assembly and the pre–1996 knock sensor, the sensors on these engines are compatible with Gen III PCMs.
The 1992 LT1 engine followed the design of the traditional small-block Chevy engine, but introduced a few improvements related to cooling, intake manifold design, and ignition system.
Generation III, 1997–2007 LS Series
A new engine design was introduced with the 1997 Corvette. The RPO “LS1” engine was also the beginning of a significantly improved engine management system. The one-coil-per-cylinder ignition system was managed by a 24-pulse signal produced by a unique reluctor wheel on the crankshaft to indicate true crankshaft position for ignition.
The 1997 LS1 engine was a redesign of the traditional small-block Chevy engine. Its intake manifold and cylinder head design are unlike the early GM engines. This LS-series engine was assembled with a 5.3L truck long block, LS2 GTO intake manifold, and LS2 Corvette front accessories.
events. While Gen I and Gen II small-block engines relied on a distributor (and any variations due to timing chain slack and camshaft-todistributor gear lash) to determine ignition events, Gen III engines have the ability to be controlled with the highest accuracy. This improved accuracy has been tested and revealed gains in both horsepower and torque. (See sidebar “John Schaefer LT1 Optispark vs. LS1 24x Ignition”on pages 10–11.) Several variations of the LS1 were released in the 1998 Camaro and Firebird and 1999 light trucks and SUVs. The 1998–2002 Camaro and Firebird used a 5.7L engine similar to the Corvette; the trucks and SUVs were equipped with new 4.8L, 5.3L, and 6.0L variations of the 5.7L LS1. Because of the interchangeability of most hardware and electronics, all of these engines are referred to generally as “LS-series” engines.
Generation IV, LS Series
Although not discussed in detail in this book, the Gen IV engines increased crankshaft position signal accuracy with 58-pulse crankshaft and 4-pulse camshaft signals. These engines use different ECMs than Gen III engines and, due to hardware and software limitations, Gen IV ECMs cannot control cable throttle systems. Although Gen IV engines can be retrofitted with Gen III crankshaft and camshaft signals, the labor required (pulling the crankshaft) is not desirable.
Written by Russell Nyberg & Jeffery Zurschmeide and Posted with Permission of CarTechBooks
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