Improving Legendary Performance With Edelbrock Gen II 426 Hemi Heads

edelbrockhemiheads-leadartBack in the ’60s, few power plants in the musclecar world garnered as much respect as venerable Hemi. For a lot of folks, the production 426 Hemi that came installed under the hood of cars like the Dodge Charger and the Plymouth Barracuda serves as the pinnacle of street performance.

This legendary reputation is one of the many reasons that these original Hemi cars are some of the most valuable vintage iron on the planet. So it’s understandable that for owners of these original cars, keeping things factory stock makes a lot of sense in terms of maintaining the car’s value.


Edelbrock’s Victor Jr. cylinder heads for the Gen II Hemi are designed for high output 426-572ci motors. They feature fully CNC ported combustion chambers and CNC blended seats for optimal air flow. Edelbrock stated that these are not factory stock replacements – that’s Mopar Performance’s department – but rather they are for aftermarket blocks that will see performance modifications. And because of the 2.32-inch intake valve diameter, an engine builder would need to eyebrow the block on the intake side with an otherwise factory stock motor.

But it’s been more than five decades since the Gen II 426 was developed, and over the years, technology has advanced dramatically – so much so that aftermarket companies like Edelbrock have found significant ways to improve upon the original design without having to reinvent the wheel in the process.

The latest case in point comes to us in the form of their Victor Jr. CNC cylinder heads for the Gen II 426 Hemi. Designed for Elephant motors with 4.5-inch bore blocks, these cylinder heads are designed to work in conjunction with the level of airflow that aftermarket 528 / 540 / 572 cubic-inch Hemis can generate, so as to unleash the full potential of these brutal big blocks. Here we’ll take a closer look at these high-flowing cylinder heads and get some insight from the folks at Edelbrock into their design and features.

Modern Tech Adds To A Proven Formula

Today, companies like Edelbrock have a number of development tools at their disposal that help engineers fine-tune their designs faster and more effectively than ever. But for a number of years, ongoing improvements for the 426 Hemi cylinder head had to be put on the back burner at Edelbrock.

Edelbrock Gen II Hemi Heads

Part # 61189


  • Combustion chamber volume: 170cc
  • Intake runner volume: 245cc
  • Exhaust runner volume: 105cc
  • Intake valve diameter: 2.32 inches
  • Exhaust valve diameter: 1.94 inches
  • Valve stem diameter: 5/16 inch
  • Valve guides: Maganese Bronze
  • Deck thickness: 5/8 inch
  • Valve spring diameter: 1.54 inches
  • Valve spring maximum lift: .700 inch
  • Pushrod diameter: 5/16 inch or 3/8 inch
  • Valve angle
    • Int. (stock)
    • Exh. Tipped 1.5 – 21.5 degrees
  • Exhaust port location: Stock
  • Spark plug fitment: 14mm x 3/4 reach, gasket seat
“For a number of years, we’ve made the aluminum cylinder heads for Mopar Performance,” explained Edelbrock’s August Cederstrand. “Over those years of casting the heads, we offered to make modifications and improvements to the design, but the Mopar folks wanted to stick to the script. In the meantime, we had a non-compete clause which prevented us from offering an alternative.”

Eventually that non-compete clause in the contract ran out, so Edelbrock was free to start developing their own Gen II Hemi heads. “We started with the basic parameters but an otherwise clean-sheet design approach and went from there,” says Cederstrand. “We incorporated all the features we’re known for – A-356 aluminum alloy construction material, heat treating to Rockwell T6 specification, hardened seats, bronze guides, helicoils in all the bolt holes – all the stuff we do to make our products easier to work with for our customers. Then we started to really consider the specific type of customer these heads would be aimed at, and it was a natural progression from there.”

Cederstrand rightfully points out that customers with original Hemi cars typically aren’t interested in modifying these rare, valuable motors, so these Gen II heads are aimed squarely at the guy building a high horsepower aftermarket Gen II 426 Hemi.

“This means we can do things outside of the stock bore size envelope,” he pointed out. “For instance, we have a 2.32-inch intake valve rather than the 2.25-inch intake valve used on the stock heads. Porting the stock head might get you there, but you’d be maxed out. Our heads flow 400 cfm as cast, right out of the box. This makes it much easier to build a 650-800 horsepower motor with an as-cast head, which saves money on porting and allows room for porting down the road if you need it.”


On the exhaust side of the equation, Edelbrock bucked conventional wisdom to some degree. “People said that we couldn’t really find improvements doing exhaust port work on these heads,” Cederstrand said. “But we thought, ‘Let’s try anyway.’”

Among other tweaks, Edelbrock's Victor Jr heads feature a revised exhaust valve angle to accommodate larger intake valves, and brass tubes are installed in exhaust pushrod holes to allow for maximum clearance with minimal port intrusion.

Using a CAD-style rendering program, Edelbrock engineers were able to create a virtual “flow box” with intake and exhaust port renderings, study the flow characteristics, and make changes where needed. This allowed them to essentially prototype their designs through these renderings before ever sending specifications to a foundry. By using molded casts of those renderings, they could even be used for a few live dyno pulls before the engine gets too hot.

We’ve been in the cylinder head business for nearly 80 years. We know a few things about airflow management and velocity. -August Cederstrand, Edelbrock

This led them to improvements like changes to the short side radius, which went against conventional wisdom. “We’ve been in the cylinder head business for nearly 80 years,” Cederstrand quipped. “We know a few things about airflow management and velocity.”

Despite the fact that these heads are aimed at builders using aftermarket blocks, Cederstrand points out that they will work with standard Gen II Hemi exhaust components. “On the exhaust side, these are a bolt-on deal. Factory exhaust manifolds, headers, etc, will work fine with them.”

In terms of performance gains, Cederstrand says that out of the box, builders should see roughly a 20-40 horsepower gain, and an equal bump in torque versus stock style heads on a motor with basic bolt-on modifications.

After running some tests with the Mopar Performance heads, a respectable 606.7 horsepower and 651.7 lb-ft of torque was achieved. Bolting on a set of Edelbrock's Victor Jr. Hemi heads, horsepower increased to 629.2, and torque came in at 646.5 lb-ft. Simply bolting on these heads was good for a power increase of 22.5 horsepower, with no other modifications. Add some other modifications to the Gen II Hemi, and you'll see even more power.

And let’s not forget about the weight savings these aluminum cylinder heads offer over the stock iron heads. While the stock bare heads weigh in at about 85 pounds apiece, these bare Edelbrock heads only weigh 29 pounds each, which means you’re taking well over 100 pounds off the nose of the car just by making this swap. That amount of mass is something you’ll notice not only in the car’s handling, but in quicker e.t.’s at the drag strip.


Just swapping out the stock iron heads for this set of Edelbrock heads, which are built from A-356 aluminum alloy, is enough to take more than 100 pounds off the front end of the car. That’s the kind of weight loss you’ll feel in handling responsiveness, drag launches, and pretty much anywhere else that weight transfer occurs.

These heads are available from Edelbrock either bare (without valves) or complete (with valves), with the latter offering a choice of configuration for either a hydraulic roller cam or a flat tappet cam.

Dual-Quad Gen II Hemi Intake

Edelbrock also offers a single-plane, dual-quad intake manifold (PN. 7524) that’s tailor-made for the kind of builds where the Victor Jr heads will shine. “We really considered the needs of the Mopar guy who would be doing this type of build,” Cederstrand explained.

“So while these guys are using 4.5-inch bore blocks for the build, they still want this stuff to fit under the factory hood and work with their factory air cleaner, Shaker scoop, etc, without having to hack things up. A high rise manifold won’t fit under the stock hood, but our dual-quad intake fits in the same design envelope as the factory manifold – while moving a lot more air.”

Edelbrock's dual-quad, single-plane Hemi intake is compatible with factory style cylinder heads, but has been optimized for use with their Victor Jr heads. Because of its Air Gap design, Edelbrock's intake also helps keep the incoming fuel/air charge cooler than the factory-style intake can. For those planning to use EFI, their Victor EFI Fuel Rail Kit (PN; 3660) will accommodate 60mm injectors.

Using a Mopar Performance 528 crate engine as the test bed, Edelbrock saw a gain of 35 horsepower by swapping over to their dual quad, single-plane manifold from the factory-style manifold that the crate motor comes equipped with.

Working in tandem with the Victor Jr cylinder heads, there’s a potential for some significant power gains above and beyond the factory style components with these two straightforward bolt on modifications, and there’s even more to be had if builders opt to use Edelbrock’s Power Package top end kits, which bundles the heads, intake, and a hydraulic roller camshaft together under one part number. This combination dished out 705 horsepower and 620 pound-feet of torque when tested on one of Mopar Performance’s 528ci crate Hemis with a 10:1 compression ratio.

Edelbrock's Power Package top end kit brings together the heads, intake, and the Rollin' Thunder hydraulic camshaft under one part number.

Looking for a hassle-free way to take your Gen II Hemi to the next level? Give the folks at Edelbrock a shout and wake that Elephant up in a big way.

Article Sources

About the author

Bradley Iger

Lover of noisy cars, noisy music, and noisy bulldogs, Brad can often be found flogging something expensive along the twisting tarmac of the Angeles Forest.
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