Ford and In­ter­na­tional Har­vester Team Up

Diesel World - - Feature -

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...

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