Dodge Gearhead: 6.4L SRT Engine Performance Specs
A lot of people just want a car to get from point A to point B, other people want a car for the driving experience provided by a beautifully crafted machine. While all engines have the same basic parts, the parts on a performance engine are not basic. Performance engines are designed to create the most power possible and that’s a science that is still evolving today.
Dodge has a few different types of performance engines including the engines on the Charger, Challenger and Viper. Here’s a close look at the 6.4-liter HEMI V8 engine, and what each engine part does and how it makes the engine a performance engine.
6.4-liter HEMI V8 powered by SRT
First, let’s introduce the 6.4L SRT engine. The 6.4L SRT engine is available on the Dodge Charger and Challenger lineups. This engine produces 485 horsepower and 475 lb-ft of torque and helps the Dodge Charger to accelerate from 0-60 mph in the low four-second range and hit a top speed of 182 mph.
Powered by SRT = Dodge’s Engineering Team
“Powered by SRT” means that the engine was specially designed by Dodge’s Street and Racing Technology (SRT) team. This team is dedicated to producing and perfecting Dodge’s line of performance models. They are responsible for the 6.4L SRT engine, the 6.2L SRT Hellcat engine and the 8.4L V10 engine on the Dodge Viper.
6.4L = Engine Displacement
6.4-liter is the size of the engine’s displacement. Most people think of engine displacement as the size of the car’s engine, but really it is the volume of the vehicle’s cylinders and/or the volume of air displaced by the action of the pistons. More cylinder volume means there is more room for air, and more air makes bigger combustions, and bigger combustions create more power.
A 6.4-liter engine is equivalent to 392 cubic inches because both measurements are different units of expressing engine displacement. Today in the U.S., liters are the most common unit used when discussing engine displacement, but cubic inches were commonly used prior to the 1980s. 392 cubic inches is the reason the Charger and Challenger trims with the 6.4L engine are named Charger SRT 392 and Challenger SRT 392.
To determine engine displacement, the number of cylinders and the size of the bore and stroke of the cylinders must be known. These numbers are then plugged into a formula. While bore and stroke are not pieces of information provided in the name of the engine, the number of cylinders are.
V8 = Number of Cylinders
This engine has eight cylinders and they are located in the engine block and placed in the shape of a “V,” hence the term, V8. Cylinders are made up of many parts and the cylinder combustion chamber or cylinder heads are where the fuel is burned and turned into power.
Since cylinders are where power is produced, a cylinder and all of its parts are very important to an engine’s performance. Overtime engineers have tweaked and improved various cylinder parts to help the engine to maximize performance and handle all of the heat and pressure that is created.
Now on to a few of the special engine parts that help to make this engine a performance engine.
HEMI is a reference to the type of combustion chamber head on each cylinder and it is actually a very important aspect to engine performance and power. A HEMI is a hemispherical combustion chamber and its unique shape provides some benefits. One of the main benefits to HEMI combustion chambers are the decrease in heat loss, so fuel in the combustion chamber burns more efficiently. A second benefit is that there is more room for valves, another very important detail in power and performance.
Oversquare Engine: Bore and Stroke
Bore and stroke refers to the size of an engine’s cylinders. The 6.4L SRT engine is an oversquare engine, which means that engine’s cylinders have a greater bore (diameter of the cylinder) than its stroke (length or distance traveled by piston from 0-180 degrees), making the bore/stroke ratio greater than 1:1. Oversquare engines allow higher rpm (and thus more power), without excessive piston speed.
The bore and stroke of the Dodge Charger 6.4-liter engine is 4.09 inches (bore) and 3.72 inches (stroke). This makes the bore and stroke engine of nearly 1.1:1. The SRT Hellcat engine (the other SRT performance engine) has a slightly smaller engine displacement (6.2-liters), but the engine is more powerful (707 horsepower and 650 lb-ft of torque) and it has a larger bore:stroke ratio (1.15:1).
Compression ratio is another factor that affects performance and engine power. The only thing that creates engine power is the size of the explosion of fuel and air in the combustion chambers and more compression creates a bigger the explosion. Once compression ratios start to get bigger, regular fuel can start to ignite before the spark plugs ignites and this can cause problems. So to prevent that from happening, manufacturers recommend or require higher octane fuel (can withstand a greater compression before igniting) on engines that have higher compression ratios.
The 6.4L SRT engine has a compression ratio of 10.9:1, which is significantly higher than the 3.6L engine’s compression ratio of 10.2:1 or the 5.7L HEMI engines compression ratio of 10.5:1. Premium gas (highest octane) is recommended for the 6.4L SRT engine, whereas midgrade gas is recommended for the 5.7L HEMI and regular gas is recommended for the 3.6L engine.
Engine valves are what control the air and fuel intake into the cylinder and combustion chamber, a very important process. There are two types of valves, intake and exhaust valves.
The 6.4L SRT engine has 16 valves with sodium-filled exhaust and 16 hollow stem intake valves. Since the exhaust valves are the valves responsible for the bringing the hot air out of the combustion chamber, they are filled with a sodium mixture because that mixture cools the air in the exhaust and allows the valve to handle more heat.
Intake valves are the valves that let the air into the combustion chamber and the easier it is for the valve to open and the more air that gets in, the bigger the explosion. So the lighter the intake valve, the easier and faster it is to open. Therefore, valves that are hollow are lighter, and they improve performance.
The materials used in engines are extremely important to an engine’s performance. Performance engines work very hard and temperatures get very, very hot, so the engine needs to be made from materials that can withstand a lot of pressure and heat.
The 6.4L SRT engine is made of deep-skirt cast-iron block with cross-bolted main bearing caps, aluminum-alloy headers. While the deep-skirt cast-iron block and alloy aluminum heads are the materials used on the 3.6L Pentastar V6 engine, the cross-bolted main bearing caps are special performance modifications. Cross-bolted main bearing caps are actually cast into the ending block and they strengthen the block so everything stays intact and does not break when maximizing engine power.
Next up, the SRT Hellcat engine and all of its glory.
Interested in a performance car?
University Dodge has the largest collection of SRT performance cars in the Southeast U.S. You can view our Dodge inventory online here.