There is no single best performance main-bearing set for every high-output engine. Choose a set made for your engine and crankshaft, then verify its dimensions and set oil clearance for the actual assembly. Bearing brand, material or coating alone cannot establish a safe fit or promise more horsepower.
What to compare before choosing a bearing set
Start with the engine family and block, then confirm the crankshaft’s main-journal size and fillet dimensions. The right part also depends on the intended oil clearance, oiling layout, operating load and duty cycle. A bearing that fits the engine family on paper may still be wrong for a particular crankshaft or build specification.
- Application and size: Verify the exact engine, crank, standard or undersize journal, thrust arrangement and part number in a current manufacturer catalog or application guide. King publishes technical information at King Bearings’ technical information page; ACL provides application-related details through its technical page.
- Material and load: Compare the manufacturer’s material and overlay options against the intended load and duty cycle. A material label by itself does not establish a bearing’s capacity for your engine.
- Oil clearance: Specify a target with the engine builder, then measure the assembled clearance. Do not assume a catalog or generic rule gives the right clearance for every combination.
- Oil delivery and bearing geometry: Check groove layout and the bearing’s relationship to the engine’s oiling system and crankshaft. More groove length is not automatically better for every design.
- Crank fillet and shell fit: Confirm the bearing’s inside chamfer or width clears the crankshaft fillet. Check the exact part against the crank, not just the engine model.
- Coating and operating conditions: Treat coatings as a possible design feature, not a replacement for oil supply, correct clearance, sound surface finish or careful installation.
How the documented product lines differ
The following are manufacturer-described features, not independent, controlled comparisons of power or service life. They help identify questions to ask after you have confirmed application fit.
| Option | Manufacturer-described features | What to verify for your build |
|---|---|---|
| King Racing | King lists high-performance aluminum and tri-metal bearings, pMaxBlack overlays, Force-105 silver-based overlay with solid lubricant additives, and polymer-coated options including pMaxKote and NitroKote. It also describes a U-groove design, narrowed bearing length for large crank fillets, and a Bulls Eye tolerance feature. See King Engine Builders and King’s TFC page. | Match the specific material, groove, coating and shell dimensions to your engine, crank fillet and oiling layout. King’s “PERFECT CLEARANCE IN EVERY SET” wording describes its Bulls Eye feature; it is a manufacturer claim, not a substitute for measuring your assembled clearance. |
| ACL Race Series | ACL describes increased eccentricity, increased crush, enlarged inside-diameter chamfers and extended-groove main bearings. Its HX suffix indicates 0.025 mm (0.001 in) extra clearance for that ACL product convention. Details are on ACL’s technical page. | Confirm that the exact part number and suffix suit the engine and crank. The HX designation is not a universal clearance target or a direction to add that amount to every bearing. |
| ACL 6B2500H example | ACL describes this specific product as having 3/4-grooved main bearings intended to optimize bearing load-carrying surface area and oil flow to the connecting-rod bearings. See the 6B2500H product detail. | This is an example of a product-specific groove design, not a recommendation for engines that do not use this application. Check the catalog listing for your exact engine. |
What the design claims do—and do not—tell you
Materials, overlays and coatings
King describes pMaxBlack as an overlay using a proprietary nanoscale hardening process intended to provide high load capacity, and Force-105 as a silver-based overlay containing solid lubricant additives. These are King’s descriptions of its products, not independent proof of a particular load limit or longer life.
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- Package Dimensions: 29.845 H x 5.842 L x 12.065 W (centimetres)
- High-load, long-duration racing such as circle track, off-road, off-shore, and others that require performance bearings.
- Package Weight: 0.612 kilograms
- Country of Origin : Israel
King says its NitroKote polymer-coated bearings are designed to withstand metal-to-metal contact and extreme loading from 10,000 HP Top Fuel engines. That is a manufacturer statement about an extreme racing application, not an independent 10,000-HP rating for all NitroKote bearings or a reason to select the product for an unrelated street or competition engine. ACL describes its CT-1 coating as a dry-film lubricant and reports oil-temperature reductions as large as 8–11°C (15–20°F); ACL does not detail the test conditions in the cited technical-page description, so that figure should not be assumed for another engine or installation. See ACL’s technical information.
Grooves, eccentricity and fillet clearance
Groove geometry affects both oil delivery and the bearing surface available to carry load. ACL’s 6B2500H illustrates a 3/4-grooved design, while King describes a U-groove option; compare the exact shell layout with the engine’s oiling arrangement rather than treating one pattern as universally superior. ACL also says its Race Series increased eccentricity is intended to help compensate for bore distortion at high speed and assist hydrodynamic oil-film formation. That is ACL’s design explanation, not a guarantee for every engine.
Rank #2
- Standard Size Bearings will be sent.
- If you require oversizes, send a message immediately.
- If King is out of stock, we will substitute Clevite A Series or ACL Brand A Series
- Send a message to check current stock of King
Crankshaft fillets are another fit constraint. King lists narrowed bearing length to clear large fillets, and ACL describes enlarged inside-diameter chamfers. The relevant question is whether the specific shell clears your crankshaft while seating correctly in the block and cap.
Set main-bearing oil clearance for the assembled engine
Main-bearing oil clearance is the space between the crankshaft journal and the installed bearing surface. It must be established for the actual parts and operating plan. ACL notes that additional clearance is often desired in high-performance use and select fitting, but its HX designation is a product-specific extra-clearance convention—not a universal target.
Rank #3
- Complete Standard Size Main Bearing Set: Includes a full set of five standard-size LS main bearings for complete engine installation, making this kit ideal for Gen III and Gen IV LS rebuilds, stock refreshes, and performance bottom-end assembly using factory crankshaft dimensions.
- Fits Gen III and Gen IV LS Engines: Designed for 4.8L, 5.3L, 5.7L, 6.0L, and 6.2L LS-based V8 engines, including LS1, LS2, LS3, LS6, LQ4, LQ9, L92, L94, L76, L77, LY6, L96, and other common LS car, truck, SUV, and swap applications.
- SI-Series Performance Design: Engineered for stock and performance LS engines using factory crankshafts, delivering dependable oil control, improved durability, and reliable bearing performance for street builds, rebuilds, and higher-output LS combinations.
- Bi-Metal Silicon Aluminum Construction: Built with a bi-metal silicon aluminum design that provides excellent load capacity, wear resistance, and long service life while supporting proper bearing function in demanding Gen III and Gen IV LS engine environments.
- Improved Crankshaft Surface Conformity: Designed to help smooth microscopic surface imperfections on nodular cast iron crankshafts, supporting improved bearing life, reduced wear, lower vibration, and quieter operation during long-term engine use.
Clevite’s 2016 performance catalog excerpt identifies several variables that affect clearance decisions: component geometry, oil viscosity and temperature, engine load, shaft diameter, coating and the ability to measure accurately. Use that list as general context, not current application-specific instructions; consult the bearing and engine manufacturer guidance for the build in front of you. The catalog is available as a 2016 Clevite Performance Engine Parts Catalog.
- Agree on the target. Have the engine builder or machinist establish the target for the engine, crankshaft, oil and duty cycle. Do not choose a figure solely from a brand comparison or a generic online rule.
- Confirm the parts. Verify the bearing part number, journal size, shell thickness and any clearance-related suffix against the current application information.
- Measure the assembly. Measure the relevant journals and installed bearing clearances with appropriate tools and record the results. A nominal size or a brand’s tolerance feature does not tell you the clearance in your assembled engine.
- Resolve differences before assembly. If measured clearance misses the agreed target, consult the machinist or bearing supplier about the cause and correction. Do not assume a coating or a different brand will fix a dimensional mismatch.
Keep thrust clearance separate from oil clearance
Main-bearing oil clearance and crankshaft thrust clearance (end-float) are different measurements. ACL’s FAQ gives general thrust-clearance ranges by journal diameter: up to 70 mm, 0.10–0.15 mm; 70–90 mm, 0.15–0.20 mm; and over 90 mm, 0.20–0.25 mm. These are ACL’s general FAQ ranges for thrust/end-float, not main-bearing oil-clearance targets. Check the engine-specific specification before using them. See ACL’s FAQ.
Rank #4
- Bearing size: STD
- Package Dimensions: 18.288 H x 4.318 L x 9.144 W (centimetres)
- Package Weight: 0.454 kilograms
- Country of Origin : China
A practical selection checklist
Before ordering, take these details to the engine machinist or use them to verify the manufacturer’s application listing:
- Engine family, block and exact bearing application
- Crankshaft make or specification, measured main-journal size and crank fillet dimensions
- Standard or undersize bearing requirement and thrust-bearing configuration
- Agreed main-bearing oil-clearance target and method for measuring the assembled clearance
- Oil-pump and oiling layout, intended oil viscosity and expected operating temperature
- Expected load and duty cycle, including street use, track use or sustained competition
- Whether the selected groove, material, overlay or coating is approved for that application
No cited source establishes through an independent controlled comparison that one brand or coating universally makes more power or lasts longer. Choose the correctly documented bearing for the exact engine and measured assembly, not a claimed universal winner.
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Quick Recap
Best Value
- Package Dimensions: 13.208 H x 4.572 L x 9.144 W (centimetres)
- Package Weight: 0.499 kilograms
- Country of Origin : Israel
- Fit type: Vehicle Specific
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
