Pure Grunt

With no provision for a spin-on oil filter, the Iron Eagle demands an external unit. We used the Moroso PN 22285 Omni Filter which accepts the same type of fine screens as the old Oberg units and can be easily disassembled to inspect and clean the filter. Installation requires four 12x12-pipe adapters from Earl's and a few feet of -12 AN line.

The challenge with a big-cubic-inch engine is keeping the compression ratio low enough, but that was solved with extreme-duty blower pistons (PN 194888) with 36cc dishes. The Dart block was milled to a deck height of 9.3125 to achieve zero piston deck clearance. Combined with Fel-Pro 1004 head gaskets, the big small-block has 9.3:1 compression, running easily on 87-octane even with the smallest cam and biggest loads. Tim Martindale at Dougan's blueprinted the heads and determined that the 1.427-inch-diameter valvesprings included with the Dart assemblies would work with both the cams we wanted to run: Spring heights were 1.760-inch intake, 1.775 exhaust, and set up at 150 pounds seat pressure and 370 pounds at 0.600 lift.

When we explained our low-rpm, high-torque dreams to the guys at Dart, they recommended the company's Pro 1 aluminum head castings with 215cc intake runners, 75cc exhaust runners, and 2.05/1.60-inch valves. These flow about 275/180 cfm at 0.600-inch lift and 28 inches of water and are considered serious performance heads for a 383- or 406ci engine. On a 450 they seem tamer: The flow numbers are similar to those of good pocket-ported GM 049 large-oval-port big-block heads but with a smaller cross-section, adding up to the high-velocity heads we were looking for. The Dart Pro 1 215 heads are available with either 64cc or 72cc chambers and straight or angled plugs, and we went with the angle-plug 64cc versions (PN 11511122).

The only specialized components required for the Iron Eagle block are the raised-cam timing chain (PN 3146KT) available through Comp Cams and the longer pushrods to compensate for the tall deck height. Dougan's normally specifies custom-length pushrods to perfect the rocker geometry, anyway, and we ordered 'rods from Terry Manton at Manton Pushrods. In this case, one pushrod length happened to work with the 1.6:1 Pro Magnum chromoly steel rockers (PN 1306-16) and both of the Comp Cams hydraulic roller cams we tested (see the dyno test sidebar). If you use a mechanical fuel pump, a longer big-block-type pump pushrod is required.

Dart sells intakes designed for the tall-deck block, but we opted to use Dart's spacers (PN 622100002) so that we could use any normal manifold. They needed significant massaging on the Bridgeport mill at Dougan's to get them to fit properly, and two sets of intake gaskets are needed (Fel-Pro PN 1206, in this case). The gap at the end seals is too big to bridge with RTV alone, so Jeff Jacobs stuck together two sets of the adhesive cork-end seals and glued them in with RTV. The taller manifold position will also require a distributor with an adjustable slip collar, and we used MSD PN 85561.

All our naturally aspirated testing was done with Dart's Kool Can dual-plane, open-valley-style intake (PN 4281100) that was port-matched to the 215 heads. The carb is a Holley HP 950-cfm vacuum secondary (PN 0-80497-1) with the stock 78-square jets, 6.5 power valves in both ends, and a 1-inch four-hole spacer. The only problem with the carb is the lack of a large vacuum port for power brakes; an adapter for a spread-bore Quadrajet might be a better off-road option. The valve covers are Dart PN 68000010 cast aluminum, which need holes bored in them for breathers.