Cometic C15515-040 LS 6.0L MLS Head Gasket Pair – 4.030″ Bore, .040″ Thickness
Upgrade your GM LS engine’s cylinder head sealing with the Cometic C15515-040 Multi-Layer Steel (MLS) Head Gasket Pair. Designed for compatible 6.0L LS-based V8 engines, this two-gasket set features a 4.030-inch gasket bore and .040-inch compressed thickness, making it an excellent option for performance engine rebuilds, cylinder head repairs, and carefully engineered forced-induction applications.
Whether you’re rebuilding a Chevrolet LS2, refreshing a GM LQ4 or LQ9 truck engine, or preparing a modified LY6 or L96 for increased horsepower, dependable cylinder head sealing is critical to engine performance and reliability.
The Cometic C15515-040 uses multiple layers of stainless steel with engineered sealing features to help maintain combustion pressure while separating coolant and oil passages.
Key Features and Benefits
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Complete Pair of Head Gaskets: Includes two Cometic C15515-040 gaskets, one for each cylinder bank of a compatible LS V8.
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Multi-Layer Steel Construction: Stainless steel layers and specialized sealing surfaces help maintain sealing integrity through repeated engine heat cycles.
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4.030-Inch Gasket Bore: Designed for compatible GM LS engines with appropriate cylinder bore dimensions.
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.040-Inch Compressed Thickness: Provides a defined gasket thickness for engine assembly, combustion chamber volume, and piston-to-head clearance calculations.
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Performance-Oriented Design: Suitable for properly assembled naturally aspirated, turbocharged, supercharged, and nitrous-assisted applications.
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Precision Engineered: Helps seal combustion chambers, coolant passages, and oil passages between the cylinder heads and engine block.
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Street and Racing Applications: An option for daily-driven performance vehicles, engine swaps, and competition builds.
Technical Specifications
| Specification | Details |
|---|---|
| Manufacturer | Cometic Gasket |
| Part Number | C15515-040 |
| Product Type | Cylinder Head Gasket Pair |
| Engine Family | GM Gen III / Gen IV LS-based V8 |
| Engine Displacement | Primarily 6.0L applications |
| Construction | Multi-Layer Steel (MLS) |
| Material | Coated stainless steel layers |
| Gasket Bore | 4.030 in (102.36mm) |
| Compressed Thickness | .040 in (1.016mm) |
| Quantity Included | 2 head gaskets |
| Listed Engine Codes | LS2, LQ4, LQ9, LY6, L76, L96, L77, LC8, LFA |
| Intended Use | Engine rebuilds and performance applications |
Fitment caution: The engine list is based on the supplied product description. Not every listed engine is a 6.0L application, and final compatibility must be confirmed against the specific engine’s bore, head design, and Cometic application data.
$220.99
Why Choose Cometic MLS Head Gaskets for Your LS Build?
GM LS engines are popular for their robust architecture, aftermarket support, and substantial performance potential. However, increased combustion pressure from turbocharging, supercharging, nitrous oxide, or elevated compression ratios can place additional demands on the head gasket.
The Cometic C15515-040 uses multi-layer steel construction designed to maintain sealing pressure between the cylinder head and engine block.
Compared with conventional composite designs, an appropriately installed MLS gasket can offer advantages in high-performance applications, particularly where cylinder pressure and temperature cycling are significant.
These advantages depend heavily on correct deck preparation, cylinder head flatness, proper fasteners, and accurate engine tuning. Planning an LS1 swap? Check out our LS1 guide here.
FYI: Why Head Gasket Thickness Matters on LS Engines
Head gasket thickness influences the clearance between the piston crown and cylinder head, often called piston-to-head or quench clearance.
The .040-inch compressed thickness of the Cometic C15515-040 must be considered alongside piston deck height, cylinder head chamber volume, and piston geometry.
Changing gasket thickness can also alter an engine’s static compression ratio.
For example, replacing a thicker gasket with a thinner one generally reduces combustion chamber clearance volume and increases static compression ratio, assuming all other dimensions remain unchanged.
This makes accurate engine measurements essential before choosing a gasket for a high-compression or forced-induction LS build. Need to troubleshoot your LS1 Build?
FYI: Check LS Block Deck Warpage Before Installation
One of the most important steps in installing MLS head gaskets is verifying that the cylinder head and engine block provide suitable sealing surfaces.
Our technical guide, How to Check an LS1 Block Deck for Warpage Before Installing the Heads, explains how to measure deck flatness using a precision straightedge and compare measurements against the applicable engine specifications.
The article discusses reference limits of 0.004 inch within a six-inch area and 0.008 inch across the deck. These are reference figures for the covered LS1 procedure, not a substitute for Cometic’s specific MLS surface requirements.
How to Install Cometic MLS Head Gaskets on an LS Engine
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Remove the cylinder heads following the applicable GM service procedure.
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Inspect both cylinder heads for cracks, distortion, and damage.
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Clean and inspect the block decks without scratching the sealing surfaces.
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Verify cylinder bore dimensions and the surface finish required by Cometic.
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Position the new MLS gaskets over the cylinder head alignment dowels.
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Install the cylinder heads using the appropriate head bolts or studs.
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Follow the correct tightening sequence, torque specifications, and fastener lubrication requirements.
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Reassemble the engine, refill fluids, and inspect for leaks.
Installation tip: Do not assume that aftermarket cylinder head studs use the same torque specifications as factory GM head bolts.
Frequently Asked Questions
Does the Cometic C15515-040 fit a 6.0L LQ4 or LQ9?
These are listed applications for the gasket. Confirm the cylinder bore, cylinder head configuration, and engine modifications before ordering.
Are these head gaskets suitable for turbocharged LS engines?
Yes, MLS construction is commonly used in properly engineered forced-induction engines. Reliable sealing still depends on boost pressure, combustion tuning, surface preparation, and head clamping.
Does the C15515-040 fit an LS3?
The gasket is listed for GM Gen III/IV engines, but a standard LS3 has a 4.065-inch cylinder bore, which is larger than this gasket’s 4.030-inch opening. Do not use this gasket on a standard-bore LS3.
Are head bolts included?
No. This listing includes two head gaskets only.
Do I need additional gasket sealant?
Cometic MLS gaskets are generally installed without supplemental sealant when the manufacturer specifies dry installation. Always follow the current Cometic instructions.
Upgrade Your LS Engine with Cometic Head Gaskets
From naturally aspirated LS rebuilds to carefully planned turbocharged and supercharged combinations, proper cylinder head sealing is essential for performance and engine longevity.
The Cometic C15515-040 LS MLS Head Gasket Pair offers precision-engineered, three-layer steel construction, a 4.030-inch gasket bore, and .040-inch compressed thickness.
This Pro Street Online bundle includes two matching head gaskets for compatible GM LS-based V8 engines.
Shop performance engine gaskets and LS rebuild components at Pro Street Online
Specification: Cometic C15515-040 LS 6.0L MLS Head Gasket Pair – 4.030″ Bore, .040″ Thickness
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