Big-Block Heads Shootout - The Big O Vs. The Big R

9 Our shortblock featured a 4340 forged steel crank and rods from Scat. The 4.250-inch stroker crank combined with the .60-over pistons to increase the displacement to 496 cubic inches.

10 JE pistons supplied the necessary forged slugs for our build up. The small-dome pistons were employed to keep the static compression ratio over 10.0:1, but the chamber volume of the heads tested varied from a low of 107 cc to a high of 123 cc (a change of more than 1 full point).

11 Proper sealing is important on any motor but critical on a test motor. Total Seal provided the necessary ring package to ensure that ever ounce of compression was used to move those pistons.

12 Milodon came through with a complete oiling system, including a pan, pick up and windage tray. The kit included a new oil pump, hardened pump shaft and main studs to properly locate the windage tray.

13 Combining our roller cam with a late-model, Gen-6 block necessitated use of a .300-tall solid roller lifters from Comp Cams. Comp also supplied a number of different sets of pushrods to work with all the different head combinations.

14 Wanting to increase power relative to the 468 used in part 1 to test to oval-port heads, we stepped up the cam for our 496. The Comp 300BR14 cam offered .652 lift, a 255/262 duration split and 114-degree LSA.

15 Since the solid roller cam was designed for a mark IV BBC, use in our Gen 6 block required not only removal of the cam retaining plate but also a dedicated front cover from Comp Cams. The two-piece, aluminum front cover provided the necessary room to run a double-roller timing chain on the Gen 6 stroker.

16 All heads for the test were secured using Fel Pro 1047 head gaskets and ARP head studs or bolts. The different heads required different length studs/bolts, but ARP supplied everything needed to complete our head test.

17 Comp Cams also came through with a set of 1.7-ratio, aluminum roller rockers.

18 Induction chores were handled by an Edlebrock Victor Jr. 454-R intake and Holley 950 HP carb. The lone exception was the AFR set that used a 454-O intake designed for oval-port heads.

19 We specified a spring package designed for the .650-lift roller cam, but three of the heads came equipped with insufficient spring pressure for the test. The stock heads, Summit iron and Edelbrock heads all required a valve spring upgrade. The stock heads received a spring upgrade from Comp Cams, while the Edelbrock and Summit heads were run with the spring package borrowed from the Brodix heads.

20 Prior to running on the engine dyno, all heads were tested on the Super Flow 600 airflow bench. Testing on the same day with the same fixtures allows for a direct comparison.