Filling the bores is a set of Arias pistons, which are specific to the Arias/Shelby Hemisp
Capping the cylinders is the crowning jewel of the combination, the Arias/Shelby cylinder heads. Arias started from the ground up in developing these cylinder heads, beginning with flow-box mock-ups to develop the port configuration, and then seeing the design through casting and final machining. The hemispherical port layout features dramatically raised runners, giving a line-of-sight straight shot into and out of the cylinders. As might be expected, airflow is abundant, with the CNC finish-ported versions delivering 409 cfm peak, and over 300 cfm available from the exhaust. Arias used a relatively shallow combination of valve angles, at 15 degrees, intake, and 16 degrees, exhaust. The valve angles allow for a much smaller chamber volume than older Hemi designs—a decided advantage when considering the compression ratio achievable with a flat-top piston. Arias offers the cylinder head in two chamber variations, the full round 74cc hemisphere design used in this engine, or a “Pro Stock” inspired figure eight–shaped version at 67cc with quench pads. The central spark plug location enhances the combustion characteristics.
What truly makes this engine package unique is the Arias/Shelby top end package. Arias has
Trefz expanded upon the performance benefits of the Arias/Shelby head configuration: “The hemi opens to the center of the cylinder. It’s not shrouded like a small-block or big-block Chevy. Sometimes you put a bigger valve in one of those engines, and it makes less power because the valve is crowding the cylinder wall. With the hemi, it’s opening to the middle of the cylinder, and that’s the advantage of the hemi cylinder head—it has to do with airflow. If I could build the perfect flow bench it would have a short-block on it with a piston in the cylinder, and I’d try testing with different piston configurations. It all affects how the air actually flows through an assembled engine.”
Of the more complex aspects of developing an all-new cylinder head configuration is the rocker arrangement. Here Arias was serious about quality and reliability with investment cast 4340 steel roller-tip rocker arms with dual needle bearings and H-13 lash adjusting screws. The rockers deliver a ratio of 1.82:1, intake, and 1.75 on the exhaust, with the intake and exhaust rockers riding on their own shafts at the opposite extremities of the cylinder heads. From the rockers themselves, to the shafts, supports, and mounting hardware, the engineering and manufacturing quality is second to none. To top the cylinder head, the Arias/Shelby conversion heads are mated to cast-aluminum finned valve covers with breathers, oil fill caps, O-ring seals, spark plug tubes, and hardware—all part of the package. The covers can be had in black wrinkle finish, high-luster polished, carbon fiber, or as-cast.
A reliable Melling oil pump moves the AMSOIL 0-20 viscosity motor oil through the lubricat
LTR spec’d the custom solid-roller Contreras cam as a single pattern with 268 degrees duration at .050, and a gross valve lift of .810 inch, with a lobe separation angle of 112 degrees. Trefz says: “The Hemi chamber is subject to crossflow at overlap, so extended exhaust duration tends to hurt power. On overlap, the mixture can blow right out the exhaust valve. I probably missed the mark somewhat in terms of the Engine Masters Challenge competition. I was thinking a little too much like a drag racer and focused on high-end power, rather than the low-end averages used in scoring the competition.” The radical, high-lift cam is controlled by a serious set of springs from PSI, delivering 1,010 pounds of open load. Isky EZ Roll roller lifters and Manton pushrods complete the stout valvetrain package required to cope with this kind of lift, heavy spring load, and rpm.