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What Is The Horsepower Of A 6.9L And 7.3L IDI Diesel Engines?
International Harvester made two iterations of the diesel engine for Ford. The first was a 6.9L IDI for the 1983 model year (F-250 and F350 trucks). The 7.3L IDI was made from 1988 to 1994. (A turbocharged version was produced during the last year of production).
What Is An IDI Diesel engine?
The term indirect in an IDI engine comes from the heart of the injection system that is used. In an IDI fuel system, the fuel is not injected directly into the combustion chamber. Instead, an IDI engine has a prechamber (also called a swirl chamber) located directly outside the combustion chamber. This simple chamber compresses air and then allows the fuel to be delivered from a mechanical injection pump through pintle injectors to mix with the heated compressed air.
The mixture is ignited as the hot compressed air flows into the cylinder to complete the combustion. As the piston reaches the top of the stroke, the fuel ignites from the heat of the compressed air (no spark plug is needed - the heat provides the initial combustion) and then gets forced into the chamber forcing the piston downward and subsequently giving power to the engine.
While indirect injection systems may be less fuel efficient compared to the DI applications we have today, they are less susceptible to mechanical breakdowns. Part of the reason is that IDI systems like the Ford diesel 7.3L IDI use pintle injectors which are very reliable in how they can control the fuel flow into the swirl chambers of the cylinders.
In 1993, the company offered a turbocharged variant that had better peak performance. The injection pump was tweaked, the oil pan enlarged for better cooling, and the horsepower and torque were raised significantly. The turbo design offered more power for owners, but it would have a short history as the stock engine for Ford trucks. Less than a year later the turbo 7.3L IDI went out of production.
The IDI has its limit but it does provide increased performance over a wider range of gears, and due to the less sophisticated hardware it uses, they are easier to maintain or find parts. A well-maintained 7.3L IDI can achieve close to 500,000 miles over its lifetime, which gives the motor a rich history of reliability. There is no question that the 7.3L IDI has earned its place in the canon of the Ford diesel.
Ultimately, the addition of DI systems that offered a higher displacement, increased torque, and better rated fuel economy replaced the naturally aspirated engine. The DI power stroke trucks were simply found to be more economical to run and the public seemed to prefer the injection system to the 7.3L IDI.
Are IDI Engines Reliable?
These old-school engines are known for being virtually indestructible and easy to maintain. The IDI engines are not hampered by sophisticated electronic injection systems or emissions technologies (like later diesel and gasoline engines), so they have the advantage of being effective motors for the things trucks were intended to do.
The indirect injection tended to impact fuel economy, but Ford was willing to take that chance when offering the diesel alternative. While the 7.3 might have lacked a bit in power as the current power stroke, it has excellent torque at low speeds, which meant that it could tow almost anything.
The 7.3 IDI is the best of the two types of diesel motors that IH made for Ford. The 6.9L tended to overheat and blow gaskets when strained and needed valve replacements. When the 7.3L was introduced, the bore was increased, the valves stiffened, and the heads got a larger prechamber. IH introduced a new design for the front cover to help counter seepage from gaskets and reduce the potential for leaks.
In 1993, IH developed a turbocharged version of the 7.3L with an upgraded injection pump. But the changes were short-lived because just a few months later, Ford introduced the new Navistar T444E, which eventually became the basis of the power stroke engine as it is known today.
Ford estimates the Ford/International Harvester calibration produced nearly 1.5 million IDI motors. The 6.9L 7.3L IdI diesel engines were a staple in Ford trucks in the eighties, and the 7.3 IDI is one of the most sought-after engines for classic truck restorers.
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I've spent many years selling cars, working with auto detailers, mechanics, dealership service teams, quoting and researching car insurance, modding my own cars, and much more.Read More About Charles Redding