Now equipped with a cam, cubes and compression (just under 11.0:1), our AFR-headed 555 stroker was missing only an induction system and a few finishing touches. While a dual-plane intake is usually preferred for street use, the lofty horsepower number and massive displacement all but dictated the use of a single-plane design. Looking through the list of available intakes offered for oval-port heads, we chose the 454-O from Edelbrock. Similar to their popular 454-R, the single-plane 454-O was designed for use on oval-port heads. We also liked the fact that the 454-O accepted the large 4500 (Dominator-style) carburetor. While a 4150 Ultra HP might be a better choice for street use, the two-circuit Dominators can be used successfully on many street/strip applications. Besides, Dominator carbs, especially the new Ultra Dominators, flat out just look cool, to say nothing of the extra power offered on high horsepower applications. Rounding out the induction system was a 1-inch, four-hole, tapered combo spacer from Wilson.
With the power producers now taken care of, we turned our attention to finishing off the stroker. In addition to the powerful hydraulic roller cam, Crane cams also supplied a set of hydraulic roller lifters. The Crane retro-fit hydraulic roller lifters were machined from 8620 steel billet, heat treated and assembled in house. The inherent strength of the superior 8620 material was combined with precision plunger fitment to provide proper (and consistent) bleed-down rates. The metallurgy and machining that goes into the Crane hydraulic roller lifters allows high(er) rpm use than conventional lifters. Given the intended power output and engine speed of our stroker, the Crane hydraulic roller lifters were definitely the hot set up. Crane also supplied a set of the original 1.7-ratio Gold rocker rams, hardened pushrods, and a double roller timing chain. Though the block from Procomp Electronics featured a provision for the Gen VI cam retaining plate and factory lifter retaining system, we chose a retro-fit hydraulic roller cam and cam button (and lock) to dial in cam thrust. The double-roller timing chain required a dedicated Gen VI timing cover supplied by Milodon. Milodon also came through with a complete oiling system that featured a kick-out pan with integrated windage tray, HV oil pump and pick up. ARP hardware was used exclusively for the build, starting with head and main bolts right down to the oil pump stud.
Finishing things off was an MSD billet distributor and wires, and a set of 2.25-inch dyno headers feeding a set of Borla XR1 race mufflers. Timing was set at 37 degrees and we ran the engine strictly on 93-octane fuel. Ensuring our thirsty stroker had plenty of petrol was an A1000 pump and fuel pressure regulator from Aeromotive.
After a thorough break-in procedure, dialing in the timing and air/fuel mixture, we came up just a little short. How short? Well, the hydraulic-roller cammed, oval-port headed 555 produced peak numbers of 773 hp at 6,400 rpm and 699 lb-ft of torque at 5,400 rpm. Impressive numbers to be sure, especially since the 555 stroker thumped out over 650 lb-ft of torque from (below) 4,000 rpm to 6,000 rpm, but a miss is still a miss.
Reviewing the dyno curves, we see that the torque output was acceptable, but that the power seemed to fall off at the top of the rev range. We know from our calculations that 800 hp was getting near the limit of the head flow offered by the AFR 300 Magnum heads, but the culprit was more likely the as-cast 454-O intake manifold. Look for us to remove the intake and send it out for porting before getting the motor back on the dyno for round two. Obviously the intake manifold cannot be designed for use on every combination from a stock 396 to a 555 (or larger) oval-port stroker. The intake must (by design) be a compromise between the extremes.
Knowing this, the porting should unearth additional airflow to at least allow the intake to keep pace with the Magnum heads. Since the AFR heads continue to flow well past 0.700 lift, we feel there might also be more power to be had with a slight bump in cam lift via a set of 1.8:1-ratio Crane roller rockers. The addition of synthetic oil and specialized oil and fuel treatments should further narrow the existing 27hp gap. We'll provide a brief update on the status as soon as we get it back on the dyno, but for now we'll have to be content with an oval-port, hydraulic-roller cammed Ovalnator that makes just 773 hp!