Simplicity is something most of us seek out in life, but we often take for granted how complicated the new vehicles we drive to work really are. However, there was a time when the complex, electronically controlled trucks we drive today didn't exist. In 1978, International Harvester-a leader in the commercial trucking industry-began developing a diesel engine that would power another industry leader's light-duty pickups, Ford Motor Company's 3/4-ton and 1-ton trucks. In the early 1980s, full production of the 420ci 6.9L engine began at International's Indianapolis plant for the purpose of not only powering Ford trucks and vans, but International's bus fleets as well. This correlated relationship sparked what is now a 25-year success story in which International-powered Ford trucks still consistently outsell the competition.
In its first year of existence,...
In its first year of existence, the 6.9L put out 170 hp at 3,300 rpm and 315 lb-ft at 1,400 rpm. Torque peaked at 338 lb-ft the following year due to a compression ratio increase.
Why A V-8?It has always been a mystery as to why International chose to build a V-8 diesel application for light-duty Ford pickups at a time when nearly its entire agricultural and trucking lineup consisted of inline-six designs. As it turns out, several different factors weighed heavily on the minds of International's engineers. First and foremost, both companies knew a diesel-powered pickup would sell, but they wanted to offer consumers an engine that would pull effectively and operate across a broader rpm range than a traditional inline design. Their predominant goal behind building a V-8 was to provide a diesel engine that built torque low and horsepower up high to give drivers a wider powerband than an inline-six would give. Ford and International wanted consumers to be able to have both speed and towing as options. In addition, engineers believed a V-8 would allow them to meet the new emissions standards expected in the 1980s. Prior to production, the 6.9L was subjected to more than 52,000 hours of testing, and the result was a bulletproof design that proved more powerful than GM's 6.2L diesel offered in K-series pickups.
Indirect-InjectionUnlike the direct-injection diesels, Ford's first diesels were indirect-injection engines. In this process, combustion actually begins in a prechamber between atomized fuel and compression-heated air, which then spreads into the combustion chamber. The final decision was made to utilize a Harry-Ricardo-based indirect-injection combustion system. Coined the "Comet" design, the proven induction swirl chamber in the engine's cylinders allowed for controlled, efficient, and manageable airflow. This type of design was considered very modern in its day.
The 6.9L engine's dry weight...
The 6.9L engine's dry weight was 860 pounds. In comparison, the 460ci gas engine option weighed 720 pounds.
6.9L/7.3L BasicsSimple in design, the 6.9L and 7.3L were non-turbo, naturally aspirated engines and used cast-iron blocks and heads, a Stanadyne DB-rotary mechanical fuel pump located in the front of the engine valley, and Stanadyne pintle-nozzle injectors. In 1983 the 6.9L put out 170 hp at 3,300 rpm and 315 lb-ft at a low 1,400 rpm. By mid-1983, Ford trucks equipped with the 6.9L were selling rapidly, which in turn led Ford to ask International to increase production. International agreed to the increase, which was projected to result in $100 million of extra revenue. In 1984, the 6.9L engine's compression was increased from 20.7:1 to 21.5:1, raising torque to 338 lb-ft at the same low 1,400 rpm. Horsepower did not increase. Both 1986 and 1987 proved to be years of change. In 1986, following a prior decision to sell off its agricultural division, IHC's commercial truck lines continued under the Navistar International nameplate. The following year became the interval year in which the 6.9L became the 7.3L. In an effort to increase power, Navistar increased the 6.9L's bore from 4.00 inches to 4.11, resulting in the 444ci 7.3L. Other than subtle differences, such as bigger diameter piston pins and larger head bolts, the 7.3L was virtually the same as the 6.9L. From 1988 to 1992, 7.3L engines made roughly 180 hp at 3,300 rpm and 345 lb-ft at 1,400 rpm.