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Old Iron - 1978 Ford F-250 Cummins

Vintage Ford Repower With More Power Built By Diesel Guru Piers Harry

Harry Wagner
Jul 1, 2010
Photographers: Harry Wagner
"They don't build them like they used to," is an often-uttered phrase. That truth is no more evident than with trucks. Solid axles, serviceable wheel bearings, and steel have been replaced by independent front suspension, unit bearings, and plastic. On the flip side of the coin, life is not all doom and gloom with modern diesel trucks. Indirect-injection and naturally aspirated engines have gone the way of the dinosaur. Turbochargers and common-rail engines have become, well, common. Legendary diesel guru, Piers Harry, wanted a truck that was stronger than the current offerings, yet provided more power than the trucks of old. He fulfilled his vision and did it for a fraction of the price of a new pickup.
Photo 2/14   |   1978 Ford F250 Cummins front View
Vintage Iron
It all began when Piers bought a '78 Ford F-250 six years ago. It had a 400ci V-8 gasoline engine, but that only lasted two weeks before he started gathering parts for the repower. "The fuel economy from the gas engine was atrocious," he explained. The crew cab, shortbed body still sits on the original frame, and most of the sheetmetal is factory-with the exception of the hood. Piers couldn't find a steel cowl hood for the truck, so he bought a cowl induction scoop for a Chevy and grafted it onto the stock Ford hood. The factory suspension is still going strong-thanks to the addition of Rancho RS5000 shocks-and provides enough room for 35-inch BFGoodrich All-Terrain tires on aluminum wheels. "I've actually sold the truck twice," Piers confessed, "but always with the provision that I would have the first right of refusal if the owner sold it, and the truck has always found its way back to me."
Inside the truck, the cab was retrofitted with leather seats from a Dodge Ram and power windows and door locks from LMC. A Flaming River tilt column and a Grant wheel handle the steering duties. The dash was completely reworked with a hole saw and Dremel and filled with Auto Meter Pro-Comp gauges. A total of eight gauges monitor everything from speed and fuel pressure to rpm and voltage.
Enter The 12-Valve
No diesel engine lends itself to repowers better than a P-pumped 5.9L Cummins engine, and that's what Piers chose. These engines require minimal electronics to run, offer unmatched reliability, and can be modified to create more than 1,000 hp. While Piers' Ford doesn't quite make that much, it is certainly no slouch. He started with a 24-valve engine from an '02 Dodge Ram and retrofitted an earlier 12-valve head. The block was fitted with Mahle 12-valve pistons, a Colt Cams camshaft, and the rotating assembly was balanced. The 12-valve head was ported and fire-ringed and is fixed to the block with ARP head studs to withstand increased cylinder pressure.
Photo 3/14   |   1978 Ford F250 Cummins wheels
That pressure comes from the large volume of fuel and air that are crammed into the cylinders. A Bosch P7100 913-series injection pump with a 3,000-rpm governor spring kit and a custom cam plate feeds Diesel Dynamics Extrude-Honed injectors. On the intake side, a high-pressure Holset HX35 sits on top of a low-pressure BorgWarner K31. The combination produces 55 psi of boost and routes the air into an intercooler sourced from a motorhome with an 8.3L Cummins. Piers' Cummins generates a modest 407 hp and 1,064 lb-ft of torque at the wheels.
Modern Drivetrain
Behind the engine, power is routed through an NV4500 transmission that has been upgraded with a full-splined mainshaft, upgraded nuts on the Third and Fifth gear assemblies, and a South Bend dual-disc clutch. The Overdrive gear in the NV4500 helps keep the engine speeds down much better than the original NP435 did, without sacrificing strength or the low First gear ratio. The NV4500 transmission is backed by an NP241 aluminum chaindriven transfer case. While not quite as strong as the gear-driven NP205 that it replaced, the NP241 has lower gear reduction (2.72:1 vs. 1.96:1), is significantly lighter, and runs quieter than the NP205.
Photo 10/14   |   Firestone air springs sit atop the stock rear leaf springs and are filled by an external air source. Piers uses the airbags to level the truck when he tows his 8,000-pound RV trailer.
The stock Dana 60 rear axle was replaced with a Dana 80 from an '01 Dodge Ram 2500 by relocating the axle's leaf spring pads. The Dana 80 has a larger ring gear (111/4-inch vs. 93/4-inch) and stronger axleshafts (35-spline, 11/2-inch shafts vs. 30-spline, 1.31-inch shafts) than the Ford's original Dana 60. Rear disc brakes were not a factory option from Dodge until 2002, so Piers retrofitted them onto the axle.
The only factory drivetrain component that was retained was the Ford Dana 60 front axle. These were available on the '78 to '79 F-350s, and on select F-250s with the snowplow-prep package. Unlike the ball joints and unit bearings found on current axles, Piers' high-pinion Dana 60 uses kingpins and serviceable hubs that make the axle easier and less expensive to maintain.
Photo 11/14   |   Fast Coolers aluminum coolers were added to the NV4500 five-speed in place of the factory PTO covers. They add fluid volume and cooling capacity to the transmission. Inside the bellhousing is a South Bend dual-disc clutch.
It is true that "they don't build them like they used to," but even more so, they never built them like this. Not all of us have the abilities or the resources that Piers has, but his truck certainly gives us something to strive for.



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