INSIDE FLEECE PERFORMANCE ENGINEERING’S NEW CUMMINS PERFORMANCE SERIES HEAD
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INSIDE FLEECE PERFORMANCE ENGINEERING’S NEW CUMMINS PERFORMANCE SERIES HEAD
Just like any short-block build, your cylinder head is only as good as the machine shop that put it together. Proper inspection, precision machining via state-of-the-art equipment, a good valve job, and the company’s track-record in the industry all factor into the deal—especially if you’re chasing four-digit horsepower. For ’03-present Cummins owners looking to go big, there is a lot more to it than simply adding head studs. The factory, crack-prone valve seats need to be addressed before they become a major problem, stiffer valve springs need to be added to handle elevated rpm, drive pressure, and boost, and fire rings are requisite for utmost combustion sealing.
Based on the head work it was regularly performing for its truck pull and drag race customers, the folks at Freedom Racing Engines—the engine building wing of Fleece Performance Engineering—decided to offer a competitionready cylinder head for 24-valve Cummins owners. Called its Performance head, each reconditioned unit comes loaded with some of the best components available in the aftermarket, along with its factory weak links addressed. Items such as Hamilton Cams’ 103-lb valve springs and Manley Performance stainless valves come standard, as do heat-treated, oversize valve seats, screw-in freeze plugs, fire-ring grooves and the corresponding head gasket. Better yet, Fleece has them on the shelf and ready to ship at all times.
While Fleece rates its Performance head for 1,100-rwhp, similarly built units have been used on engines making more than 2,000 hp. From usable core to finished product, join us for a look at the in-depth remanufacturing process each Performance head undergoes.
With high miles and prolonged exposure to excessive EGT, it’s not uncommon for 24-valve cylinder heads to crack valve seats or even drop them altogether, which can spell disaster in at least one cylinder, if not for the entire engine. To eliminate this potential problem, Fleece installs hardened, oversized valve seats (in both the exhaust and intake sides) that feature a radius’d edge on the side that installs face down within the head.
Like any other engine-related operation, Fleece relies on good usable cores to provide the lifeblood for its Performance cylinder head program. And because the quality of any core head Fleece receives is unknown initially, each head is stripped (valves, springs, seals, guide liners, freeze plugs), thermal cleaned and shot-blasted, and undergoes a thorough inspection before being qualified as usable.
The next stop for the Performance series head brings it to the valve seat station, but before the oversized valve seats are installed, the head’s cast-in valve guides are treated to fresh valve guide liners. The K-line bronze valve guide liners incorporate a spiral pattern that aids lubrication. After they the liners are in place, a broaching process expands them, essentially locking them in place within the valve guides.
After measuring the starting thickness of the core head, the extensive job of transforming it into a Performance version begins with the decking process. Within Fleece’s Haas VF-4SS VMC (vertical milling center), 0.003 to 0.005 inches of material is removed during a typical resurfacing, with the exact measurement being recorded on each head’s data sheet upon completion. We’ll note that the head we followed from start to finish was a unit off a 6.7L Cummins.
For maximum combustion sealing between the block and head, Fleece cuts fire rings into the fire deck of every Performance series head it sells (all fire-ring protrusion exists in the head). This high horsepower insurance policy ensures, with the help of a quality head fastener, that boost pressures in excess of 80-psi can be run without worry of blowing a head gasket. A fire-ring head gasket kit with a multi-layer steel gasket and 4.550-inch diameter mild steel rings accompanies each Performance head.
Before leaving the confines of the Haas VF-4SS, the head is machined to accept screw-in type pipe plugs in place of the 11 freeze plugs located internally on the exhaust manifold side. High horsepower, high miles, and old age can lead to the factory freeze plugs blowing out, which allows coolant to mix with engine oil. Every cylinder head that passes through the doors at Freedom Racing Engines is treated to screw-in freeze plugs.