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GM LS Engine Swap Tips

Posted in How To: Engine on March 19, 2015
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General Motors small-block V-8 engines have been popular since they were first introduced in 1955. Previously, most domestic engines were inline six-cylinder models. Over six decades, they’ve worked their way to being one of the most popular engines in the world.

These days, many engine swaps center around the GM LS engines, a modern line of V-8 small blocks with displacements ranging from 4.8 to 7.4 liters. The first LS1 engines debuted in the Chevy Corvette in 1997, and a lot of different versions of the pushrod engine have been offered over the last 17 years. Versions include cast-iron and all-aluminum engines.

It was a fresh design with respect to the iconic GM small-block that pre-dated it, so nearly none of the parts are interchangeable between the two. These newer-generation engines got no ignition distributor and use one coil per cylinder to ignite the multi-port fuel-injected cylinders. Generation III engines were built from 1997 to 2007, and Generation IV engines have been produced from 2005 to 2014. The latest generation has variable displacement by deactivating some cylinders under light power load conditions, and variable valve timing is used on some engines.

These engines have proven themselves to be reliable and well-suited for performance upgrades, so they make great swap engines. They can be used with the modern transmissions they were paired with from the factory, or fitted to older transmissions with only minor modifications.

Tanner Lamb from Lamb Fab, a custom shop in Gilbert, Arizona, shared with us a few tidbits to heed when dealing with LS engine swaps. One tip when considering buying a used engine is to pull the vehicle identification number (VIN) off the outside of the engine control module (ECM) and check it against a history report available from one of the online vendors. With this, you might be able to more confidently confirm actual engine mileage by looking at past emissions testing or other records.

Late-model GM LS engines use what are called steam vents on one or both of the engine heads. These are used to route coolant out of the top of the cylinder heads and prevent any air or steam pockets from forming in the coolant passages in the heads. They are typically also routed to the throttle body where the hot water serves to pre-heat it in colder conditions. From there, the coolant is typically routed back to the radiator. When a swap is done, it’s best to provide a return path to a high point in the low pressure side of the new radiator to force any steam pockets out of the coolant flow, eliminating air bubbles from the system. Late-model GM LS engines use what are called steam vents on one or both of the engine heads. These are used to route coolant out of the top of the cylinder heads and prevent any air or steam pockets from forming in the coolant passages in the heads. They are typically also routed to the throttle body where the hot water serves to pre-heat it in colder conditions. From there, the coolant is typically routed back to the radiator. When a swap is done, it’s best to provide a return path to a high point in the low pressure side of the new radiator to force any steam pockets out of the coolant flow, eliminating air bubbles from the system.
If you’re interested in installing an independent oil pressure sender on the engine, one possible location is in the oil cooler bypass plate above the oil filter on the lower passenger side of the block. This can be drilled and tapped to the size needed. You can also purchase a blank plate (GM PN 12577903) for this location, and drill and tap into it to install a threaded oil pressure sender. If you’re interested in installing an independent oil pressure sender on the engine, one possible location is in the oil cooler bypass plate above the oil filter on the lower passenger side of the block. This can be drilled and tapped to the size needed. You can also purchase a blank plate (GM PN 12577903) for this location, and drill and tap into it to install a threaded oil pressure sender.
GM LS engines, like most modern engines, hold good seal and resist oil leaks well. However, when doing an engine swap, it’s a good time to check the one-piece rear crank seal for any seepage while the rear of the engine is exposed and accessible. These engines have a removable rear cover as seen here. If removed, the cover needs to ideally be reinstalled with an alignment tool to properly center the seal to the crank to prevent leaks. GM now has an improved version rear cover (PN 12633579) with a revised gasket sealing pattern. GM LS engines, like most modern engines, hold good seal and resist oil leaks well. However, when doing an engine swap, it’s a good time to check the one-piece rear crank seal for any seepage while the rear of the engine is exposed and accessible. These engines have a removable rear cover as seen here. If removed, the cover needs to ideally be reinstalled with an alignment tool to properly center the seal to the crank to prevent leaks. GM now has an improved version rear cover (PN 12633579) with a revised gasket sealing pattern.
Whenever you acquire a junkyard engine or engine of some unknown history, it’s wise to take a few precautions before just firing it up after a swap. Aside from checking the engine externally for any signs of mechanical or plumbing issues, a fresh oil change is well advised. Drained oil may offer tell-tale signs as to the condition of the engine internals. If the engine has not run for some time, it’s a good idea to remove and flush the fuel rails. Lamb Fab recommends sending the injectors to a qualified shop to have them cleaned, then leakdown and flow tested. If one injector leaks down and fills a cylinder with fuel, the result could be a bent or broken piston rod. Whenever you acquire a junkyard engine or engine of some unknown history, it’s wise to take a few precautions before just firing it up after a swap. Aside from checking the engine externally for any signs of mechanical or plumbing issues, a fresh oil change is well advised. Drained oil may offer tell-tale signs as to the condition of the engine internals. If the engine has not run for some time, it’s a good idea to remove and flush the fuel rails. Lamb Fab recommends sending the injectors to a qualified shop to have them cleaned, then leakdown and flow tested. If one injector leaks down and fills a cylinder with fuel, the result could be a bent or broken piston rod.

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