The 4.5L Duramax LMK was officially announced by General Motors in 2008, where the automaker shared minimal details on the new engine platform destined for Chevrolet Silverado and GMC Sierra 1500 models beginning with the 2010 model year. The engine would have been the first diesel available in the fullsize 1/2 ton pickup truck segment since 1998, the last year that GMC and Chevrolet 1500 models were offered with the 6.5L V-8. Unfortunately, deep economic woes following the 2008 recession and General Motors eventual bankruptcy derailed the 4.5L Duramax entirely and the project was abandoned. Prototype engines were reportedly turned over as scrap, although at least one 4.5L Duramax appeared on eBay some time later. Post-bankruptcy, GM has given no indication that they intend to revitalize the 4.5L Duramax and has since developed a 3.0L inline 6 cylinder Duramax turbodiesel that became available in the Silverado and Sierra 1500 for the 2020 model year.
The 4.5L Duramax displayed several innovative features, including reverse flow cylinder heads, a weight saving compacted graphite iron engine block, 72 degree cylinder spacing, and dual overhead camshafts with 4 valves per cylinder. Reverse flow cylinder heads arrange the exhaust path into the engine valley, where the turbocharger is mounted, to improve thermal efficiency and reduce turbo lag. The engine was designed with cylinders at 72 degree separation angles to narrow the engine, likely to increase serviceability and enhance its adaptability into additional applications with more stringent spacial restraints.
A clean-sheet engine design, the 4.5L Duramax would have been designed and produced independently of DMAX, the GM-Isuzu joint venture that has manufactured the flagship 6.6L Duramax diesel since 2001. Much has changed in the segment since GM first teased the industry with its 4.5L prototype, and in reality the 4.5L Duramax was unlikely to meet GM's long term goals with regards to efficiency; the 1/2 ton segment now has three highly fuel efficient diesel options, which include the 3.0L Duramax, FCA's 3.0L EcoDiesel, and Ford's 3.0L Power Stroke.
4.5L LMK Duramax Engine Specs
| Engine Family | Duramax 4500 |
| RPO Code | LMK |
| Assembly Site | Undetermined |
| Applications/Production Years | Never reached production stage Originally intended for 2010 Chevrolet Silverado and GMC Sierra 1500 models |
| Displacement | 4.5 liters, 275 cubic inches |
| Configuration | 72 degree V-8 |
| B10 Life | Not specified |
| B50 Life | Not specified |
| Bore [1] | ~ 3.56 inches (90.5 mm) |
| Stroke [1] | ~ 3.42 inches (87.0 mm) |
| Compression Ratio | 16.0:1 |
| Engine Block Material | Compacted graphite iron (CGI) |
| Cylinder Head Material | Cast aluminum |
| Injection System | High pressure common rail Piezoelectric fuel injectors Bosch CP4.2 injection pump 29,000 psi max injection pressure |
| Aspiration | Turbocharged, intercooled (air-to-air intercooler) Single variable geometry turbocharger (VGT) |
| Valvetrain | Dual overhead camshafts, 4 valves per cylinder (32 valve) |
| Horsepower | ~ 310 horsepower |
| Torque | ~ 520 lb-ft |
| Governed Speed | Not specified |
| Emissions Equipment | Exhaust gas recirculation (EGR), diesel oxidation catalyst (DOC), diesel particulate filter (DPF), selective catalytic reduction (SCR, requires diesel exhaust fluid) |
[1] - Bore and stroke interpolated using the bore-stroke ratio from the 6.6L Duramax diesel (1.04); provided values are highly speculative and were never substantiated.
Image source: General Motors
Image source: General Motors
Editor, Diesel Hub