As the name designates, the 6.4L Hemi features hemispherical shaped combustion chambers. The hemispherical combustion chamber resembles a dome shape, although the modern 5.7L and 6.4L Hemi engines do not have traditional Hemi cylinder heads; in reality, the combustion chambers are semi-hemispherical and not entirely spherical in shape. The primary advantage of hemi cylinder heads is that the slanted angle of the intake and exhaust valves provide less restrictive breathing of the engine during the intake and exhaust strokes. A challenge of hemi engines is the flame propagation distance around the corresponding dome shaped "pop up" piston. To maximize combustion efficiency and maintain low emissions, the 6.4L Hemi relies on 2 spark plugs per cylinder. The primary spark plug initiates combustion at the appropriate time while the secondary plug fires after the power stroke is initiated.
The 6.4L Hemi found in the Ram truck line differs significantly from that available in other Chrysler products, such as Dodge Challenger and Charger models. The primary alterations in deriving the truck version include an entirely different engine calibration focused on adjusting and flattening the torque curve in addition to maximizing fuel economy. The engine is available with a Chrysler 66RFE six speed automatic transmission in applications with a gross vehicle weight rating (GVWR) less than or equal to 10,000 lbs and the Aisin AS69RC in applications with a GVWR greater than 10,000 lbs.
6.4L Hemi Engine Specs (Truck Models)
| Engine | Chrysler 6.4L Hemi V-8 | |
| Configuration/Type | 90° pushrod V-8 | |
| Applications | • 2014 - current Ram 2500/3500 pickups • 2014 - current Ram 3500/4500/5500 cab and chassis trucks |
|
| Displacement | 392 CID, 6.4 liters | |
| Firing Order | 1 - 8 - 4 - 3 - 6 - 5 - 7 - 2 | |
| Bore | 4.090 inches (103.9 mm) | |
| Stroke | 3.72 inches (94.6 mm) | |
| Compression Ratio | 10.0:1 | |
| Engine Block Material | Cast iron | |
| Cylinder Head Material | Cast aluminum, hemispherical combustion chambers | |
| Aspiration | Naturally aspirated | |
| Ignition | 8 individual ignition coils mounted near spark plugs. 16 individual spark plugs, 2 per cylinder. |
|
| Valvetrain | 2 valves per cylinder, cam-in-block (pushrod V-8) variable valve timing (VVT), hydraulic roller lifters | |
| Fuel Injection | Sequential multi port fuel injection | |
| Fuel Requirements | Regular 87 octane fuel adequate, minimum 89 octane recommended | |
| Engine Oil Capacity | 7 qts w/ filter change | |
| Engine Oil Spec | Full synthetic SAE 0W-40 meeting Chrysler MS-12633 | |
| Oil Change Interval | Replace engine oil and filter every 8,000 miles or 12 months under normal conditions Replace engine oil and filter every 4,000 miles under severe duty conditions |
|
| Horsepower | Ram 2500/3500 pickup | 410 hp @ 5,600 rpm |
| Ram 3500/4500/5500 cab and chassis | 367 - 370 hp @ 4,600 rpm | |
| Torque | 429 lb-ft @ 4,000 rpm (pickup and chassis cab models) | |
| Max Engine Speed | 66RFE automatic (<= 10,000 GVWR) | 5,800 rpm |
| Aisin automatic (> 10,000 GVWR) | 4,660 rpm | |
6.4L Hemi Features
• 16 spark plugs, two per cylinder, for improved combustion efficiency (performance and fuel economy) and reduced emissions.
• 66RFE automatic transmission ratios: 1) 3.23:1, 2) 1.84:1, 3) 1.41:1, 4) 1.00:1, 5) 0.82:1, 6) 0.63:1, R) 4.44:1
• Aisin AS69RC ratios: 1) 3.75:1, 2) 2.00:1, 3) 1.34:1, 4) 1.00:1, 5) 0.77:1, 6) 0.63:1, R) 3.54:1
• Based on the architecture of the 5.7L Hemi V-8, although they share neither bore diameter nor stroke length, which has been a part of Ram's light and heavy duty lineup since 2003.
• Aluminum cylinder heads with hemispherical combustion chambers.
• Oil-to-water oil cooler for prolonged oil life and additional engine cooling under rigorous conditions.
• Piston cooling jets spray engine oil on the bottom of the pistons to help remove combustion heat.
• Entirely capable of running on standard 87 octane gasoline, although a minimum 89 octane gasoline is recommended.