LSX Engine: What It Is, LSX vs LS, and the LSX 376-B15 Crate Engine
An LSX engine is an engine built on GM’s LSX block: a cast-iron, LS-architecture block designed for racing and high-boost builds rather than for production cars. It keeps the LS family’s basic layout, so it works with LS parts, but it adds strength where big-bore and boosted engines need it. Many people also use “LSX” loosely to mean any LS-family engine, so check which one a seller or forum post means.
LSX vs LS: what is different?
- Purpose: production LS blocks were designed for cars and trucks. The LSX is a performance block made for engines that see much more cylinder pressure, such as turbocharged, supercharged and large-displacement builds.
- Material: car LS blocks such as the LS1, LS2 and LS3 are aluminum, and truck LS blocks are cast iron. The LSX is a heavy-duty cast-iron block, so it is heavier than an aluminum LS.
- Head clamping: LSX blocks have provision for six head bolts per cylinder, and GM’s matching LSX heads are sold as 6-bolt heads. The extra bolts help keep the head gasket sealed under boost.
- Bore size: thicker cylinder walls let the LSX be bored larger than production blocks, which is how large-displacement LSX engines are built.
- Shared parts: like production LS blocks, the LSX uses six-bolt, cross-bolted main caps and accepts LS-family heads, intakes and accessories that suit its configuration.
For the rest of the family, see GM LS engines explained.
GM LSX 376-B15 crate engine specs
The GM Performance LSX 376-B15 (part 19417356) is a long block built on the LSX block and, as its name suggests, built to handle 15 psi of boost. These figures come from its specification list:
| Specification | LSX 376-B15 |
|---|---|
| Engine type | LSX-series Gen IV small block V8, long block |
| Displacement | 376 cubic inches |
| Bore x stroke | 4.065″ x 3.622″ |
| Block | LSX cast iron with 6-bolt cross-bolted main caps |
| Crankshaft / rods / pistons | Forged steel / forged powdered metal / forged aluminum |
| Camshaft | Hydraulic roller, .560″ intake / .555″ exhaust lift, 210 / 230 degrees duration at .050″ |
| Cylinder heads | LSX-LS3 rectangular port, 68cc as-cast chambers, 6-bolt attachment |
| Valve size | 2.160″ intake / 1.550″ exhaust |
| Compression ratio | 9:1 |
| Rocker arms | Investment-cast roller trunnion, 1.7:1 |
| Recommended fuel | Regular pump fuel |
| Maximum recommended rpm | 6,600 |
| Reluctor wheel | 58X |
| Rating | 473 HP |
| Price | $11,524.99 |
Building on the LSX 376-B15
- Boost: the low 9:1 compression and forged rotating assembly are what make it suitable for a turbocharger or supercharger. Plan the fuel system and tune for the boost level you intend to run.
- Intake: the rectangular-port LSX-LS3 heads need a rectangular-port (LS3/L92-style) intake manifold.
- Engine control: it uses a 58X crankshaft reluctor wheel, so pair it with a controller that supports 58X, such as a standalone ECU from our engine management range.
- Use: GM’s product note says it is designed for pre-1976 street vehicles or off-road use, not marine applications.
The rest of the swap (mounts, oil pan, accessory drive and fuel system) follows our LS swap guide. See also LS accessory drive kits.
LSX or a production LS?
For a naturally aspirated street engine, a production-based engine such as the LS3 is lighter and usually costs less. The LSX block makes sense when you plan significant boost or want the strength margin of a race block. Compare the options in LS and LT crate engines.
Frequently asked questions
What is an LSX engine?
Strictly, an engine built on GM’s LSX cast-iron performance block, such as the LSX 376-B15. Informally, many people use “LSX” for any LS-family engine.
Is an LSX the same as an LS?
It is part of the same family and shares the basic LS layout, but the LSX block is a stronger cast-iron race block with six head bolts per cylinder and room for larger bores.
Is an LSX block better than an LS block?
It is stronger, which matters for high boost and big-bore builds. It is also heavier than aluminum production blocks, so a production LS is often the better fit for a mild street engine.
How much boost can the LSX 376-B15 handle?
GM builds it to handle 15 psi of boost.
How much horsepower does the LSX 376-B15 make?
It is rated at 473 HP.
Related: GM LS engines explained, LS3 engine, LT4 engine, LS swap guide, LS firing order, LSX crate engine, all guides.
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