As for the carburetor, Holley has just the line to do the job with its Truck Avenger series. These are specially modified versions of the traditional performance carbs, built with off-road service in mind. Tech highlights include a special vent tube to prevent fuel spill-over, spring-loaded needle and seat valves for improved fuel inlet control, and a special metering block that prevents flooding even in extreme situations, up to a 40-degree approach angle, a 30-degree departure, or a roll. That's damned near any way but upside down. These carbs come in three sizes, from 470 to 770 cfm, and we went for the big one. The vacuum secondaries, and the Bronco's relatively light weight, go a long way to making such a large carb useable in this combination.
Those are the basics of how we arrived at this engine setup. With everything pondered over and thought out to the best of our ability, it was up to Speed-O-Motive to build it and then test on the dyno to prove its worth. We were on hand as Speedo's dyno operator Jake Harriston loaded the brute to the DTS pump, dialed in the baseline settings, and sparked it to life. With the open dyno headers, the 347 sounded sweet, settling into an idle that left no doubt that this was a bad boy. After an agonizingly long 30-minute run-in, we were ready for some noise with the imminent power pulls. With the torquey 347 topping the 400 mark in both horsepower and torque on the SAE scale, this thing more than doubled the factory gross power numbers. This kind of power is enough to stampede any Bronco.
 Because of the longer runners...  Because of the longer runners and pulse separation resulting from a 180-degree port layout, two-plane intakes will always make more torque down low than a single plane, and will often make as much top-end power up to 5,500 rpm or more. With the rpm range of our engine, a two-plane was the natural choice. We went with Weiand's No. 8020 Stealth, which has a low profile and plenty of performance potential. |  Holley's 0-90770 Truck Avenger...  Holley's 0-90770 Truck Avenger carb is rated at 770 cfm, which may seem kind of big for our 347, but with vacuum secondaries the engine will be more tolerant of its capacity. This carb is designed specifically for truck and off-road applications, and is packed with features to make it really work in the rough. |  A rugged and reliable ignition...  A rugged and reliable ignition system can make or break you on the trail. We used a complete MSD system, including its billet No. 8479 distributor, along with an MSD coil, wires, and 6470 control box. MSD components have earned an enviable reputation for reliability in off-road racing. |
 A further consideration for...  A further consideration for off-road conditions is an upgrade to Weiand's No. 8210 high-volume water pump. Environmental factors can get searing in the Western desert off-road playgrounds, and the Weiand pumps were developed on a unique water-pump dyno for effective flow. |  We were eager to see what...  We were eager to see what our off-road stroker would be capable of on the dyno, and Speed-O-Motive was prepared to obliged with a test on its DTS engine dyno. Dyno man Jake Harriston had the engine mounted, broken-in, and tuned-up in short order. With over 400 hp and 400 lb-ft of torque on hand in a lightweight early Bronco, it's sure to be a wild ride. | |