Installing Comp Cams’ Stage 2 HRT Valvetrain On A 6.4L Hemi SRT

We’ve written a lot about Comp CamsLow Shock Technology. To be fair, it really has revolutionized the way we look at the valvetrain and allowed for feats of power and reliability previously thought impossible. With that new technology applied to late-model Gen-III Hemi engines, it bears the name “HRT.”

While the new lobe designs not only make more power through increased valvetrain stability, that stability also increases the reliability and longevity of the valvetrain. To ensure that the end-user gets the maximum power from all the parts, Comp has matched up components into its HRT assemblies and packaged them into Stages.

There are Stages 1 through 3 for naturally aspirated Hemi combinations as well as Stage 1 and 2 assemblies for supercharged and turbocharged combinations. For this particular install, because the engine already has a few bolt-ons, Comp suggested a Stage 2 HRT assembly for the 6.4L Hemi used in this test. As a breakdown, this is what came in the kit:

Stage 2 HRT Camshaft

The camshaft used in this kit is named, unsurprisingly, “Stage 2 HRT 222/230 Hydraulic Roller Cam” (no fancy names like “Mother Thumper” here, just “Stage 2 HRT”). Designed to put its best work between 1,900 and 7,000 rpm, the hydraulic roller profile features (again, as the name suggests) 222 degrees of duration on the intake and 230 degrees of duration on the exhaust — both at .050-inch lift. Gross lift at the valve is .599 inch on the intake side and .604 inch on the exhaust, with a 115-degree lobe separation angle.

The camshaft is built on a billet-steel cam core, which is an upgrade over the factory SADI (Selectively Austempered Ductile Iron) camshaft. The billet material should hold up to increased spring loads better. The Stage 2 grind is aggressive enough that it requires the use of new valvesprings.

The Stage 2 HRT 222/230 camshaft has features besides its specs that make it interesting. The Low Shock Technology lobes are easier on the valvetrain while being more agressive profiles, and the billet core is superior to the factory ductile iron camshaft. But, if all you care about are specs, the Stage 2 cam features .599/.604 inch of lift at the valve, with a split duration of 222 and 230 degrees at .050 inch of lift, with a 115-degree lobe separation angle.

Beehive Valvesprings

Part of the whole Low Shock Technology theorem is that even with the more aggressive ramps, lighter spring rates can be used. To pair with the Stage 2 cams, the beehive springs (P/N: 26918) are rated to a maximum lift of .625 inch at the valve, with a seat pressure of 125 pounds, and an open pressure of 367 pounds. The 1.075-inch/1.310-inch O.D. single spring is a proven performer in the LS lineup and works equally well in the Gen-III Hemi platform.

To complement the beehive spring, Comp includes a set of steel spring locators, hardened steel 7-degree triple radial-groove valve locks, and the matching 4140 chromoly steel valve retainers. Additionally, Comp includes a set of positive-stop PTFE valve seals as well.

With the LST lobe profiles, you don’t need monster valvesprings to control aggressive lobe ramps. These single beehive springs with only 125 pounds on the seat are more than capable in this combination.

Lifters and Pushrods

Like the GM DOD or AFM cylinder deactivation systems, Dodge’s Multi-Displacement System (or MDS) uses more complicated lifters as part of the system. So, like the LS and LT engines, Comp includes a set of traditional lifters to remove potential failure points in the system.

While a lot of enthusiasts simply opt for the OEM Hellcat lifter, the Comp lifter is designed to have increased oil retention around the roller axle and bearing. The kit also includes a set of four new lifter yokes (similar to the LS lifter trays, for those not familiar with the Gen-III Hemis).

To ride on the new lifters, the Stage 2 HRT assembly also includes a new set of Hi-Tech pushrods. The .080-inch wall-thickness hardened seamless chromoly pushrods measure 6.800 inches on the intakes and 8.100 inches on the exhaust and should hold up to the engine’s demands nicely.

Much like GM's DOD or AFM, you need new lifters to properly eliminate Dodge's multi displacement system, and those are included in the package. Also included are hardened .080-inch-wall Hi-Tech pushrods in the proper lengths for the intake and exhaust valves.

Phaser Limiter

While there is no arguing the benefits of variable valve timing in improving an engine’s economy, in the performance realm, huge swings in cam timing can lead to an unintended meeting between the pistons and valves. To solve this, the included phaser limiter kit prevents the camshaft from varying more than 7 degrees. This ensures adequate piston to valve clearance even with larger camshafts.

On The Dyno

Before the team at Livernois Motorsports started tearing into the engine, the car was strapped down to the chassis dyno. The Challenger posted peak baseline numbers of 433.5 horsepower at around 5,780 rpm and 452.9 lb-ft of torque at 3,800 with a little torque plateau from 3,600 rpm to about 4,300 rpm.

While the team at Livernois simply pulled the engine from the bottom of the car to perform the upgrades, part of that was to give our cameras better access to the process. These upgrades could absolutely be performed with the engine still in the engine bay. In addition to the Stage 2 HRT assembly, the coils were also upgraded using a set of FAST Hemi XR coils. The upgraded electronics provide 15-percent more spark energy delivered at 40,000 volts while fitting just like factory units.

With all the upgrades in place, the car was strapped back onto the Livernois dyno, and after some quick tuning for the new components and the deleted MDS, we were rewarded with new peak numbers of 487.6 horsepower at 6,060 rpm and 513.6 lb-ft of torque at 4,060 rpm. That makes for a peak power increase of 54.1 horsepower and 60.7 lb-ft of torque.

As you can see, the power gained with the package was significant. In addition to picking up 54 peak horsepower and 60 lb-ft of torque (at the wheels), it shifted the peaks up about 200 rpm each.

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About the author

Greg Acosta

Greg has spent fifteen years and counting in automotive publishing, with most of his work having a very technical focus. Always interested in how things work, he enjoys sharing his passion for automotive technology with the reader.
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