LS & SBC Bare Blocks: What to Know Before You Buy
A bare block is the foundation of every engine build. It’s the casting — the cylinder bores, main saddles, and deck surfaces — with nothing bolted to it. No crank, no pistons, no heads. Just iron or aluminum waiting for you to build something on top of it.
If you’re building a custom engine from scratch, a bare block is where it starts. Here’s how to pick the right one.
What Is a Bare Block?
A bare block is an engine block that’s been stripped, cleaned, inspected, and machined — or in the case of new blocks, cast fresh. It includes:
- The block casting itself
- Main caps (installed and line-honed)
- Freeze plugs and oil galley plugs (new)
- Cam bearings (installed in most cases)
That’s it. Everything else — crankshaft, pistons, connecting rods, camshaft, timing set, cylinder heads — you source and install yourself.
Who buys bare blocks? Engine builders, hot rodders, racers, and anyone doing a ground-up custom build where they want to choose every single component that goes into the engine. If you just need a replacement engine to get a truck back on the road, you want a long block, not a bare block.
SBC Bare Blocks (Small Block Chevy)
The traditional small block Chevy — the 350, 383 stroker, 327, 305, and their cousins — has been the backbone of American performance building since the 1960s. SBC bare blocks are everywhere.
What to Look For
2-bolt vs. 4-bolt mains: Four-bolt main caps hold the crankshaft more securely. For builds over 400 hp or engines that will see sustained high RPM, 4-bolt is preferred. For a street 350 making 300 hp, 2-bolt mains are perfectly fine.
Casting number: The casting number (rear driver’s side of the block) tells you the application, year range, and sometimes the cylinder wall thickness. Some castings are more desirable — the 010 block (casting 3970010) is a proven 4-bolt main, thick-wall casting popular with builders.
Bore size: Standard 350 bore is 4.000″. Most cores have been bored at least once. A .030″-over block has thinner walls but is still safe for a street build. At .060″ over, you’re pushing the limits — sonic-check the walls before committing.
Siamesed vs. non-siamesed cylinders: Most SBC blocks have non-siamesed cylinders (coolant passages between all cylinders). This is fine for most builds but limits how far you can overbore compared to siamesed designs.
Common SBC Bare Block Builds
SBC Bare Block Pricing
LS Bare Blocks
The LS engine family replaced the traditional small block starting in 1997. It’s lighter, stronger, and flows better than the old SBC platform. LS swaps are everywhere — Camaros, C10s, Miatas, you name it. LS bare blocks are the starting point for modern performance builds.
Iron vs. Aluminum
The 5.3L truck block (LM7, L33, L59, LC9, LH6) is the go-to budget LS bare block. They’re everywhere thanks to massive production numbers in Silverados, Sierras, Tahoes, and Yukons. An iron 5.3 block bored to 3.905″ and stroked to 4.000″ makes a 403 ci LS-based engine with serious potential.
Common LS Bare Block Options
LS Bare Block Pricing
What Machining Should Be Done?
A bare block should arrive ready to assemble — meaning the following machine work is already done:
- Bore and hone to final size with proper crosshatch pattern for ring seating
- Deck surfacing to ensure head gasket sealing surfaces are flat and true
- Line hone (main saddles checked and trued for crankshaft alignment)
- Freeze plugs and cam bearings installed
If you’re buying a used block from a junkyard or private seller, budget $400–$800 for machine work at a shop before it’s ready to build on. A remanufactured bare block from a reputable seller should have all of this done already.
Remanufactured vs. Used vs. New Aftermarket
For most builders, a remanufactured bare block is the sweet spot. Machine work is done, bore size is known, and it comes crack-checked and ready to assemble. New aftermarket blocks like the Dart SHP or GM LSX Bowtie are for high-horsepower applications where you need the thickest walls and strongest castings available.
Where to Buy
Bishop Car Parts carries remanufactured bare blocks for SBC and LS applications — cleaned, machined, inspected, and ready to build. Direct-to-consumer pricing on the GM platforms we’ve specialized in since 1948.
