Ford and International Harvester Team Up
IH started development work on a V8 diesel for medium-duty trucks in 1978. The architecture was based on the company’s own 446cid industrial gas V8. “Ack!” you may say. “A conversion!” Not really. The diesel merely adopted similar block dimensions that made tooling up easier. It isn’t exactly clear when Ford Motor Company’s interests were piqued by the IH diesel, but in 1981 a $500 million agreement was signed for IH to develop the engine for Ford light and medium-duty trucks and to supply engines for five years. Because it was a hefty engine, more than 900 pounds, it was soon clear this was going to be a three-quarter ton and up powerplant. When the diesel option emerged for 1983 it cost $2,225.
The Ford diesel light trucks debuted in late 1982 as ’83 models. The lightest duty truck in which the 6.9L (420cid) diesel was available was the F250HD (8,600-pound GVW) and they went all the way up the light line, including the E-series vans and into the Ford medium duties. The first advertised rating was just 161 hp and 307 lbft with a 19.7:1 compression ratio. These were likely preliminary specs because 170 hp and a 20.7:1 compression ratio very soon became the advertised norm.
Cranking out 420 cubic inches from a 4-inch bore and a 4.18-inch stroke, the 6.9L featured oil-cooled pistons, four-bolt mains, a massive forged crank with a 2.2-inch rod and 3.1-inch main journals, valve rotaters, roller tappets, geardriven cam and injection pump. It was naturally aspirated and indirectly injected using the Ricardo V combustion chamber. Injection came from a Stanadyne (Roosa-master) DB2 rotary pump and pintle-type injectors that were popped at 2,100 psi. Issues with cold starting came right away, so in ’84 the compression ratio was raised to 21.5:1. Torque increased to 315 lb-ft as a result. That’s where output would stay for the remainder of the 6.9L run that lasted through 1987.
The engine got a makeover for 1988. The bore was increased 0.18-inch and that boosted displacement to 7.3L (444 cid). The heads, head bolts, head gaskets, rocker gear and combustion chambers got a workover and the glow system was completely revised. The injection system also got some tuning alterations. As a result, the engine was boosted to 180 hp at 3,300 rpm and 338 lb-ft of torque (some spec sheets show 345 lb-ft). In mid-year 1992 power output was increased to 185 and torque went up to 360. The 1992 model year also brought a serpentine belt system.
The revisions in the 7.3 were largely successful but there were some stumbles. The overbore and cooling system changes resulted in an increased tendency toward cavitation damage on the cylinder walls in the water jacket. It was manageable using the right anti-corrosive coolant additives (called SCAS, supplemental coolant additives) but it became a well-known problem.
The IDI reached its zenith late in 1993, when the first 7.3L turbo was introduced. It mounted
The 7.3L IDI debuted in 1988 and touted a number of improvements. Power was advertised at 180 hp and torque bumped to 338 lb-ft. The engines looked similar on the outside and initially they only came naturally aspirated; 7.3L blocks can be...
The original 6.9L diesel from 1983 evolved rapidly. The first big change was a boost in the compression ratio from 20.7:1 to 21.5:1. The ’83 blocks, casting number 1805440C1, were problematic due to possible cracking issues. As a result the...