427ci Windsor Ford Arias Hemispherical Head Conversion - Deep Breather

When it comes to building custom performance engines, there are numerous choices in terms of what direction to take. For many, improving the OEM design theme is accomplishment enough, using replacement-style parts that offer to significantly improve output. For the likes of Nick Arias Jr., getting the most from an engine means starting with a clean sheet of paper, and then making the parts in accordance to his uncompromising all-out performance ways. As Arias likes to put it, “You can make a great street engine from a race engine, but you can’t make a great race engine from a street engine.” A case in point is the 427-cube Ford featured here. Using a hemispherical cylinder head conversion developed by Arias, the engine is capable of phenomenal output in a race configuration, while the same basic package can be built for reliable street duty with outstanding performance.

The Build

Naturally, you don’t cut corners when building an engine like this, so Trefz filled the bottom end with some of the best components the aftermarket has to offer, starting with a Scat billet steel crank cut for 1.88-inch Honda journals. Trefz explains: “The small journals reduce rotating mass and inertia, and cut friction through the reduced bearing speed. I was basically building a NASCAR-style bottom end.” The aluminum block will expand more than a comparable iron unit, so special consideration is given to the main bearing clearance. Trefz points out: “As the block grows, so does bearing clearance, so the mains are set up tighter than with an iron block. Working out the details of what is appropriate given the material is all part of the build process.”

Attached to the crank are Carrillo rods and gas-ported Arias pistons specific to the top end combination. Trefz had the pistons cut for very narrow-section .8mm compression rings from Total Seal. As Trefz explains, “The narrow ring actually provides more unit loading on the cylinder wall for a very good compression seal. The gas ports supply pressure to the back of the ring, while the surface area is reduced due to the thinner profile.” The combination worked extremely well, with Trefz reporting negligible leakage past the rings when testing leakdown, and a combustion space that was very clean after running.

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.

“You can make a great street engine from a race engine, but you can’t make a great race engine from a street engine.” —Nick Arias Jr.

“Capping the cylinders is the crowning jewel of the combination, the Arias/Shelby cylinder heads.”

“The valve angles allow for a much smaller chamber volume than older Hemi designs…”