A few decades ago most engines had a piston cylinder that had a flathead design. This engine had a number of flaws, such as low compression ratio, poor combustion chamber shape, and poor gas flow.
The Hemi engine, however, has a hemispherical cylinder head that maximizes volume and minimizes surface area. As a result, it generates more power with minimal heat and energy losses. This engine has gained popularity mostly because of its incredible performance that outweighs its limitations.
The Hemi engine concept is constantly evolving. Today we’re going to be comparing the 6.1 vs 6.4 Hemi and help you figure out which of these two versions is the better option for you.
Main Difference Between 6.1 Vs 6.4 Hemi
These are the main differences between 6.1 and 6.4 Hemi:
- The 6.1 Hemi has a displacement of 370 cu in, whereas the 6.4 Hemi has a displacement of 392 cu in.
- The 6.1 Hemi produces 425 horsepower at 6000 rpm, whereas the horsepower of the 6.4 Hemi ranges from 366-485 hp at 4600-6000 rpm.
- The 6.1 Hemi generates a torque of 420 pounds force foot at 4800 rpm, whereas the torque of the 6.4 Hemi ranges from 429-475 pounds force foot at 4000-4800 rpm.
- The compression ratio of the 6.1 Hemi is 10.3:1, whereas the compression ratio of the 6.4 Hemi is 10.9:1 for SRT and 10.0:1 for trucks.
- The 6.1 Hemi has a bore and stroke of 4.06 and 3.58 inches respectively, whereas the 6.4 Hemi has a bore and stroke of 4.09 and 3.72 inches respectively.
- The 6.4 Hemi has the Multiple Displacement System (MDS) and Variable Valve Timing (VVT), whereas the 6.1 Hemi doesn’t
What Is 6.1 Hemi?
Key Highlights
- 425 hp horsepower
- 420 ft-lb torque
- 10.3:1 compression ratio
- Sequential multi-port fuel injection
- V configuration, 8 cylinders, and 2 valves per cylinder
- Cast iron cylinder block
- Aluminum cylinder head
- Gasoline fuel
- 4.06-inch bore and 3.58-inch stroke
This is a V8 6.1-liter gasoline engine that was first introduced into the market in the Chrysler 300C SRT-8 in 2005. Several race-proven engine technologies were combined to engineer the 6.1 Hemi. The engine’s production lasted up to 2010. It was featured in other vehicles, including Jeep Grand Cherokee, Magnum SRT-8, Charger SRT-8, and Dodge Challenger SRT-8.
The 425 hp produced by this engine is impressive. But torque is equally as important as horsepower because it makes a car fun to drive. The manufacturer of the 6.1 Hemi didn’t disappoint with a massive 420 pounds force foot of torque at 4,800 rpm.
It has a deep-skirt cast-iron engine block that is integrated with coolant channels and bulkheads to provide a total displacement of 6.1 liters. The engine block is also equipped with oil squirters for cooling the pistons.
The crankshaft of this engine is forged steel and the connecting rods feature powder metal material. It has flat-top pistons that have a larger diameter for handling increased compression ratio.
The cylinder heads of the 6.1 Hemi have a unique port design that features a bigger cross-sectional area. This outstanding design increased flow in the intake as well as the exhaust ports. The engine has a multi-port fuel injection system with an increased fuel injector flow capacity when compared to the 5.7-liter version. This allows the engine to handle higher airflow and speeds.
The 6.1 Hemi meets the minimum EPA emissions standards. It also has good reliability, reasonable fuel economy, and durability.
What Is 6.4 Hemi?
Key Highlights
- 366 to 485 horsepower
- 429 to 475 pounds force foot
- Cast iron cylinder block
- Aluminum cylinder head
- Gasoline-powered
- MDS
- V configuration, 8 cylinders, and 2 valves per cylinder
- Variable valve timing
- A bore of 4.09 inches and stroke of 3.72 inches
- A compression ratio of 10.9:1 for cars/SUVs and 10.0:1 for trucks
Chrysler and Dodge started getting back into the Hemi vehicles in the early 2000s. By 2006 these two brands had five different SRT8 vehicles, including the Challenger, Charger, Magnum, Grand Cherokee, and Chrysler 300. These vehicles were operated by the 6.1 Hemi. But by 2010 Chrysler replaced the 6.1 Hemi with the 6.4 Hemi.
This improved version of the Hemi became available in 2007, but the 6.1 Hemi lived on in production. The 6.4 was first launched in the Dodge Challenger SRT8 in 2011 with MDS and variable valve timing in cars with automatic transmissions. The multi-displacement system will shut off four cylinders under specific conditions to save fuel. This feature is found in all automatic transmission applications. The benefits of the MDS are fewer parts, maximum reliability, and lower cost.
The 6.4 Hemi has a few different names like 392 Hemi for its cubic inches of displacement and reference to the first generation 392. The 2014 model year heavy-duty cab chassis and trucks were available with the revised version of the 6.4 Hemi. The engine displacement size is imprinted on the front fender emblems as well as the engine coil pack covers.
The 6.4 Hemi engine features hyper-eutectic pistons along with oil squirters to minimize heat. It also has a floating pin that is attached to a powdered metal connecting rod.
The boar is 4.09 inches, the stroke is 3.72 inches, and the crankshaft is made of forged steel. These specs are the same on all 6.4 engines. The compression ratio is higher in cars and SUVs at 10.9:1. It is lower in trucks at 10.0:1 because of piston design change. The higher compression ratio in cars and SUVs is just one aspect of being able to produce more power.
Features Comparison
Here are the key features that will help you understand the difference between 6.1 vs 6.4 Hemi:
Multiple Displacement System (MDS)
The 6.4 Hemi comes equipped with the Multiple Displacement System or MDS, while the 6.1 Hemi doesn’t. What this system does is turn off four of your eight cylinders.
The V8 engine generates more power and uses a lot of gas. Selectively deactivating four of the cylinders is said to improve the fuel economy of the 6.4 engine. The solenoids located inside the engine are going to collapse the valves for the intake as well as the exhaust.
At the same time when the valves are closed, the PCM shuts down the spark and injector to the corresponding cylinder. This system has a lot of intricate parts that rely on engine maintenance. So, poor maintenance can cause the system to shut down and the engine will run without the MDS.
The MDS is included in the 6.4 Hemi to help boost fuel economy and reduce the number of emissions getting pushed out into the atmosphere.
There are a few issues, however, that are associated with the MDS like lifter problems, MDS turning on and off, and dropped valve seat.
Variable Valve Timing (VVT)
The next noticeable difference between these two Hemi engines is variable valve timing. The 6.4 Hemi comes with the technology, while the 6.1 Hemi doesn’t.
The intake valves open to let the gas and air into the cylinder, whereas the exhaust valves open to allow the burned gas and air out of the cylinder. Having said that, valves are controlled by camshafts. A mechanical system like the one found in the 6.1 Hemi runs the same way at all RPMs as well as all the engine loads. This is usually not ideal for horsepower, fuel economy, and emissions.
To improve horsepower, fuel economy, and emissions, the manufacturer included variable valve timing in the 6.4 Hemi. This technology changes three parameters of the engine, valve lift, valve duration, and valve timing.
Computer-controlled variable valve timing smoothens out engine performance by optimizing the fuel and air mixture inside the cylinders at different engine speeds. At higher speeds, the intake valves open earlier enough, wider, and for longer periods to deliver maximum air and fuel for boosted power. The overabundance of gas at lower rpm would be wasted, causing rough idle. So, the variable valve timing technology causes the valves to admit less air and fuel.
Related: 5.7 Hemi Longevity and Maintenance Tips
6.4 Vs 6.1 Hemi – Verdict
Which one should you choose? You can conclude which one is better for your application by going through the differences.
The 6.1 Hemi is a very simple and basic engine, considering that it doesn’t have a multiple displacement system and variable valve timing. It has a traditional fuel injection, which doesn’t rely on technology to generate power. But with the 6.4 Hemi, you get a boost in horsepower and torque and much better flowing cylinder heads. The MDS and VVT also add to fuel economy and better emissions in the 6.4 Hemi.
So, ultimately the 6.4 Hemi seems to be the better option, based on our findings.