CHI Cylinder Head Innovations

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An All – New, All – Aussie Alloy Cylinder Head Breathes New Life Into Mopar Sixes
Courtesy of Street Machine Magazine
Story: Craig Parker | Photos: Cristian Brunelli

During the early 70’s, racetracks Australia-wide were terrorised by 265ci six-cylinder Hemi-powered Charges. Although only sporting six pots, these tough mills were no slouches. They were more than capable of leggin’it with the best V8’s of the day.

John Konstandinou from Cylinder Head Innovations could clearly see the 265’s potential and began toying with them more than 15 years ago. Over the ensuing years, John has managed to develop the Hemi into an even more formidable horsepower producer.

To achieve the lofty power levels John was chasing, it was necessary to have the standard Hemi head extensively cast-iron welded. This is an expensive ($1500) and time-consuming process, which is why Cylinder Head Innovations decided to take everything they knew about six-cylinder Hemi heads and incorporate that knowledge into a completely new aluminium casting.

The primary design goal was to create a head that could bolt up using standard components with a minimum of fuss. As good as the standard head was, Cylinder Head Innovations’ new offering will flow almost 390hp (90hp more than standard) straight out of the box. If you want to push the performance envelope, invest in bigger valves, bowl work and some solid porting and it can flow up to a tyre-frying 450hp. To back up his claim John campaigns a Super Sedan LJ Torana with one of his 400hp Hemi sixes – which has set a low ET of 10.438 seconds.

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For low-production manufacturing, sacrificial sand-casting is the way to go. With all the R&D finalised, a set of wooden master patterns are made. From these masters patterns, a set of epoxy-resin patterns are fashioned which are used to create the actual sacrificial sand moulds. Two sets of patterns are needed in case one is damaged.

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This is where the fun begins. Resin impregnated sand is poured into the mould. The resin bonds the sand together to form a very-soft sandstone-like consistency. In the more intricate areas, the sand is actually packed or compressed into all the small cavities by hand using prodders and other things.

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Once the impregnated sand has cured (around 30 minutes), retrieving the sand moulds from the individual patterns is as easy as turning the box upside down, giving it a sharp thump and a good shake, and out it pops.

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Here are all the individual pieces (cores) that hold up the mould. Note the coarser grade of sand used for the water jacker pieces. This reduces the production of gas which causes undesirable air pockets to form when the aluminium is poured. Coming up with the correct recipe/blend of sand and resin for each piece is an art unto itself.

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It’s necessary to hold all the individual pieces in the correct position. To achieve this they’re essentially glued in place. A super-high temperature PVA glue is used to accomplish this and is specially formulated for this task. With each piece set in place the PVA glue is allowed to set for around 30 minutes before pouring.

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It takes two of these (a top and bottom halve) to create a completed mould. Note the keyway around the edge of the sand-mould so that the two halves fit together in perfect alignment.

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Ingots of A601 aluminium (five percent silicon) are melted in an electric furnace. Ceramic ladles, each capable of holding around 10 kilos of molten metal – are used to scoop the 700-degree Celsius aluminium out of the furnace. The foundry crew has just 40 seconds to pour the molten metal into the mould before it cools excessively.

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This is the most spectacular part of the whole process. Upon pouring, super-heated air rushes out of the breathers and a vile sulphur stench is given off as the bonding resin in the sand gets scorched. To prevent air pockets from forming, it’s critical that both people begin pouring at exactly the same time, and at precisely the same rate.

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Generally the heads are cast in lots of three. Note the heavy weights atop the mould. these are in place to stop the heads from bowing as they begin to cool. As you’d expect the sand itself gets very hot when filled with molten aluminium – a great place to be around during winter, not so good in summer!

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Hammer time! This is why it’s called sacrificial casting. After allowing things to cool for 24 hours, a deftly wielded sledgehammer is perfect for smashing the sand mould away from the casting. Along with poking and prodding, an impact driver-like device is also used to hammer the head, dislodging the sand from the ports and inner passageways.

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Looking a bit like a five-funnel Titanic, they can be pretty agricultural with the head at this point as there’s is up to an extra five millimeters of material on most of the surfaces.

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Note the roughness of the casting (a trait inherent in all sand-cast objects). Thorough machining is required for nearly every surface, however before any machine work is commenced the head is first heat-treated. A fortunate side-benefit of the heat treating process is that it dislodges and remaining sand still trapped within the casting.

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Many hours of precision machining is required to turn a raw casting into an functioning head. The first machining process is to deck the head. The machinist (John) uses this surface to reference all the other machining processes.

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Astute Mopar enthusiasts will note that the head is set up for non-standard screw-in rocker studs and roller rockers. The roller rocker’s themselves are an ‘off-the-shelf’ Yella Terra Hemi item, but they require the installation of 7/16 mounting studs.

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Finishing off the valve train side of the head is press-in cast-iron valve guides, fitted with a K-Line insert. Cut into the head is oversized valve spring seats. This allows the new head to accept oversized springs, up to the largest size currently available.

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As with any alloy head, the head is machined to accept hardened, press-in valves seats. While machining the head to accept these steel seats, a dial indicator is used to ensure that each seat is cut exactly the same depth.

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Naturally Cylinder Head Innovations’ new casting configuration allows the fitment of oversized valves, up to 2.02-inch inlet and 1.65-inch exhaust. The customer is able to specify whether they want a three or five-angle valve job.

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With standard-sized valves the new casting flows over 390hp, while the laid-back spark plug angle promotes good combustion. Since these heads were intended for street applications, the combustion chamber was sized to keep comp between 9.5 and 10.0:1.

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Throughout the entire machining process each and every aspect of the head must be checked and double-checked. Especially considering that the casting allows numerous combustion chamber and valve diameter configurations.

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Raw versus fully machined. It takes around 20 hours of solid machine work to complete all of the necessary machining processes, including a small amount of hand finishing in the combustion chamber and around the throats. With everything finished, all that’s left to do is bolt the head up and give it a whirl!

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While designing and building a dedicated race head would have been fun, there’s just not the market to support such a product. Therefore Cylinder Head Innovations have deliberately kept their new head standard in configuration so that all the standard ancillaries (exhaust / inlet manifolds, pistons and block) can be retained.

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While not absolutely necessary for street application, it’s recommended you invest in a good stud girdle set-up if for you’re competing your 265 Hemi. The girdle will have to be custom-made; however, as stated, the rockers are standard 265 Hemi Yella Terra items.

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Ready to roar in anger. With today’s high-tech gaskets, retorquing the head after break-in is not necessary, but use an anti-seize compound on the bolts to stop them from gauging the aluminium. Once again, depending on application, either a regular composite gasket (street) or copper gasket (race) can be used.

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To take advantage of the heads dramatically increased breathing capability, give it plenty of airflow. Triple 50mm Webers do the trick nicely. One drawback of the alloy head is its sensitivity to engine coolant. It must be run with coolant, but not too much otherwise destructive corrosion will set in.

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When the flag drops the bullshit stops! Although intended as a street head, Cylinder Head Innovations’ new casting has proved itself pretty handy on the racetrack. A 400hp version of the alloy-headed 265 Hemi bolted into the engine bay of John and brother Michael’s LJ Torana has powered it to a best of 10.438 seconds – with more to come!

Nine good reasons to spend up big

1. The design, construction and materials are compatible with unleaded fuels

2. Alloy construction allows head to run cooler, thus alloying higher compression ratios on pump gas

3. Flows an extra 90 horsepower out of the box

4. With porting, will flow up to 450 horsepower!!

5. Small-diameter spark plug is laid over and angled towards the exhaust port

6. Raised exhaust port provides for better flow characteristics

7. Smaller kidney shaped combustion chambers allow for higher compression ratios to be easily achieved

8. Greater quench area to help reduce detonation

9. Standard intake and exhaust manifolds will bolt straight up