What’s in My Challenger’s Head? Valvetrain Parts Explained

The cylinder head is mounted on top of the engine block. It basically closes the top of the cylinder to form the combustion chamber. The cylinder head in your Dodge Challenger will also house the intake and exhaust valves, rocker arms and valve springs.

Seated in each combustion chamber are three valves (5.7L Hemi): two for intake, one for exhaust. These valves open in accordance with the engine cycle and either allow the air to flow into the chamber (intake cycle) for combustion or for the exhaust gas to flow out of the head (exhaust cycle). During the compression and power cycles, the valves are held firmly closed by a spring seated atop the cylinder head. Indirectly actuating the valves is the camshaft, which turns at half the rate of the crankshaft.

The camshaft has special lobes ground into its profile, and as the cam turns these lobes press a pushrod up and down. The opposite end of the pushrod activates a rocker arm which then opens the appropriate valve. Of course, all of this requires very specific geometry and timing.

The main difference between standard and HEMI cylinder heads is the Hemispherical design of the combustion chamber. This design allows the cylinder head to be equipped with larger valves to improve airflow. Another advantage of the HEMI cylinder head is the smaller surface area. The Hemispherical design of the combustion chamber has less area which better retains the heat within the chamber. In a typical high-performance motor, the goal is to lose as little of the heat as possible when the engine burns the air and fuel mixture. Heat is responsible for creating high pressures inside the cylinder which is ideal for performance applications.

Now, the modern day Chrysler Hemi combustion chambers look like more of a semi-hemispherical design, as the chamber has been squared off somewhat. This is to promote quenching and swirling of the combustion mixture, which ultimately leads to more complete combustion, more power, and better fuel efficiency. Don't let any old timers try and tell you that it isn't a real Hemi! While the new Challengers may not mirror the same iconic hemispherical chambers of their predecessors, the newer revised chambers produce a lot more power and use a lot less fuel to do so!

Most OEM engines will typically come with cast-iron cylinder heads. Cast-iron is the preferred material because of two factors: durability and cost. Cast-iron cylinder heads are cheaper to mass-produce and can withstand higher temperatures.

But there’s a catch. Cast-iron cylinder heads are heavy. The material is also less-efficient in terms of dissipating heat. When it comes to performance or racing applications, shaving off a couple of pounds will not only mean the difference between winning and losing, but it will also mean a better handling car.

Such is the reason why American, Japanese, and European carmakers slowly shifted to aluminum alloy cylinder heads. Aluminum offers significant weight savings over gray cast iron. It also offers better cooling as the alloy is able to dissipate heat much better than iron. This allows the tuners to increase the compression ratio with a lesser risk of pre-ignition or detonation.

But aluminum cylinder heads also have their quirks. The material is not as stiff and can degrade rapidly when constantly exposed to extreme temperatures. As a basis for comparison, an aluminum and iron cylinder head will comparably have the same strength at room temperature. But when exposed to temperatures of 400-degrees Fahrenheit or higher, the cast iron cylinder head will be twice as strong as aluminum.

It all depends on the type of engine. In the 2019 Dodge Challenger V6, the 3.6-liter motor has a 60-degree V-type and liquid cooled design. The cylinder head houses double overhead or DOHC camshafts with 24 valves. The valvetrain is chain-driven with hydraulic end-pivot rocker arms. The set-up allows the V6 motor to churn out 305-horsepower and 268 pound-feet of torque on unleaded regular 87 octane fuel. This V6 motor also benefits from an aluminum alloy deep-skirt engine block and aluminum alloy cylinder heads.

The 2019 Dodge Challenger R/T with a 5.7-liter HEMI V8 is equipped with 16 pushrod-operated overhead valves with roller followers. The Fuel Saver Technology feature in this motor allows eight of the valves to deactivate while the other eight valves are run by conventional hydraulic lifters to save fuel. The HEMI motor is constructed using a deep-skirt cast-iron block. The aluminum alloy cylinder heads are equipped with the famed Hemispherical combustion chambers. Power output is rated at 375-horsepower and 410 pound-feet of torque.

In the 2019 Dodge Challenger R/T Scat Pack, the HEMI V8 is equipped with eight sodium-filled exhaust valves and eight hollow stem intake valves for a total of 16 valves. This motor is built with a deep-skirt cast-iron block and aluminum alloy Hemispherical cylinder heads to produce 485-horsepower and 475 pound-feet of torque on premium 91 octane fuel.

The Challenger SRT Hellcat is equipped with a supercharged 6.2-liter HEMI V8 motor with 16-valves, a deep-skirt cast-iron block, and aluminum Hemispherical cylinder heads. Power is rated at a brutish 717-horsepower and 656 pound-feet of torque courtesy of dual water-to-air intercoolers and a twin-screw supercharger. The high-output version of this motor can produce 797-horsepower and 707 pound-feet of torque in the Challenger SRT Hellcat Redeye. It has the same pushrod-operated overhead valvetrain with 16-valves and hydraulic roller lifters.

Yes. For instance, it is entirely possible to swap the cylinder head of a 2003 to 2008 HEMI to the cylinder head of a 2009 Gen 3 model. In this case, the block and the internals will be mostly the same, but it’s not the end of the story. The stock camshafts, pushrods, and lifters on the old cylinder head will need to be replaced. This also includes the exhaust manifold and the engine CPU. In most cases, the push rods can be reused provided they are still in excellent condition but the lifters, in particular, should be replaced with new parts.

You can ask any MOPAR gearhead. While the power output of the Gen3 HEMI 5.7-liter and 6.1-liter is nothing to scoff at, the motor will respond well to specific valvetrain upgrades.

For example, the stock beehive valve springs in the 5.7 and 6.2-liter HEMI are excellent for stock applications. But after bolting in a set of camshafts with a more aggressive cam profile, the stock OEM valve springs are not enough. In this case, upgrading the valve springs are a good idea.

After considering the valve springs, the stock valves should be considered as well. A set of aftermarket or custom valves with lower valve lock grooves will move the retainer position downwards to accommodate larger-diameter straight-type valve springs. The 5.7-liter can also make use of custom valves to improve flow and horsepower. The trick is to swap the stock 2.00/1.55-inch valves from the 5.7-liter to a set of 2.08/1.600-inch valves derived from the 6.1-liter HEMI. This alone will enable the 5.7-liter HEMI to benefit from a 7-percent improvement in flow to improve performance.

The cylinder head in the 6.1-liter HEMI has larger rectangular ports, which allows 20-percent more port volume compared to the cylinder head in a 5.7-liter (with smaller and nearly square port openings). Swapping the cylinder heads in this regards (and swapping the valves) will enable your 5.7-liter Challenger to produce more horsepower with better throttle response.

The good news is both the cylinder head castings in the 5.7 and 6.1-liter HEMI share the same bolt spacing, external thread accessory positions, valve angle geometry, and cast spark plug wells. As with all engine rebuilding projects, it is always best to seek the recommendations of a professional engine builder.