Chevy 505ci Big Block Cylinder Heads - Freedom Flow

Removing a set of valves reveals a nice five-angle valve job ground to Patriot's proprietary specs.

The valve-seat contours are hand-blended into the runners on both the intake and exhaust sides. Patriot Performance will CNC-bowl-blend and gasket-match your chosen head for and extra $200; full CNC porting costs $450 extra.

Rectangular intake ports measure 320 cc, small enough to help create low-rpm torque but large enough to support high-rpm power.

The lifter cup height in Isky's Red Zone roller lifters is identical to that in its solid lifters, so if you use them on a stock head, stock-length pushrods will work. Patriot Performance, however, uses "plus length" valves (0.250 inch on the intake, 0.100 inch on the exhaust) to allow for the installed spring heights needed with today's high-lift camshafts. JMS used a measuring pushrod to determine the correct pushrod length, which turned out to be 0.100 inch longer than stock.

We topped this combo off with a Victor Jr. intake, a Mighty Demon 850 carb and fuel fittings, and a Mallory 32 Series Comp S/S distributor that was ready to run.

To make sure we got every bit of lift and duration out of our cam, we installed a set of 1.75:1 roller rocker arms-this is the ratio Isky uses to calculate its big-block cam specs. The cam card called for 0.028-inch hot lash on both the intake and exhaust valves. Jeff Johnson set this clearance, then went back and reset it once the engine was hot.

Once the valves were set, it didn't really take long to dial this combo in. The Mighty Demon was spot-on out of the box, and the engine liked 38 degrees of total timing. We liked the big power numbers-and gobs of torque-this Patriot-headed, Isky-cammed setup made.

We decided to run Isky's Red Zone solid roller lifters. The oil holes make sure the needle-bearing rollers stay lubed under the low-oil-pressure, high-heat conditions they'll see on the street. If these lifters do wear out, don't worry-they're fully rebuildable.