6.9L & 7.3L IDI Diesels

International 6.9, 7.3 Diesel Specs, History, & Information

The 6.9L and 7.3L IDI engines, developed and built by International Harvester and the later International Navistar, predate the technology savvy Power Stroke engine family. Simplistic in nature, the IDI engines are rugged and dependable, albeit comparatively short on power by today's standards. The International 6.9 and 7.3 IDI engines produce honest, respectable power figures with reasonable fuel consumption. The 6.9 was only offered as a naturally aspirated engine, while the 7.3 was offered in both N/A and factory turbocharged applications.

International 6.9L IDI Diesel

Development of the 6.9L IDI began several years before Ford and International would commence their relationship in the diesel pickup sector, which would last nearly 30 years. And neither Ford nor International knew at the time that this engine would eventually lay the foundation for one of the most successful diesels ever offered. The 6.9L IDI was introduced for 1983 model year Ford 3/4 and 1 ton F-Series pickups. It was available with a 4 speed manual or 4 speed automatic transmission, though a 5 speed variant was offered during its last production year. At 170 horsepower, the 6.9L was never a speed demon, but it produced a respectable 338 lb-ft at only 1,400 rpm. And by nature of being a diesel, its fuel economy capabilities far exceeded that of all Ford's gassers with comparable torque output. Completely mechanical, the 6.9L is relatively easy to maintain and repair. Despite having a fraction of the performance potential of modern diesels, the 6.9L IDI earned itself the reputation of being a reliable workhorse, and the pickups still make honest work and farm trucks today.

6.9L IDI Specs

Engine:

International Harvester 6.9L IDI V-8 diesel

Years Offered:

1983 to 1987 model year Ford Trucks

Displacement:

6.9 liters, 420 ci

Compression Ratio:

20.7 : 1 for 1983 MY, increased to 21.5 : 1 for 1984+ MY

Bore:

4.00 inches

Stroke:

4.18 inches

Aspiration:

Naturally aspirated, never offered with factory turbocharger options

Injection:

Indirect injection (IDI), mechanical injectors, Stanadyne rotary style injection pump

Valvetrain:

2 valves per cylinder, standard OHV, camshaft in block

Peak Horsepower:

170 hp @ 3,300 rpm

Peak Torque:

338 lb-ft @ 1,400 rpm

 

International 7.3L IDI Diesel

The 7.3L IDI is based on the 6.9L IDI engine platform, the 7.3L having a marginally larger cylinder bore. The extra displacement resulted in a modest bump in horsepower and just over 20 extra lb-ft of torque. In 1993, a turbocharged version of the engine was released, which pushed torque to nearly 390 lb-ft. Since the 7.3L is a high compression engine, the turbocharged versions proved to be marginally less reliable, as the engine was not originally designed with turbocharging in mind. The 7.3L has slightly larger head bolts than the 6.9L, contributing to a more robust design. The cylinder walls of the 7.3L are thinner than the 6.9L, and as a result cavitation in the water passages is a concern (cavitation is the formation of small vacuum pockets in a liquid, in the case of an engine this can erode the cylinder walls over time). However, using the appropriate SCA/DCA (supplemental coolant additive/diesel coolant additive) eliminates this risk. The 7.3L IDI was replaced mid-model year for 1994, when Ford/International released the 7.3L Power Stroke. The two engines share displacement and dimensional characteristics, but the direct injection Power Stroke is much more than an adaptation of the IDI.

7.3L IDI Specs

Engine:

International/Navistar 7.3L IDI V-8 diesel

Years Produced:

1988 to 1994 model years

Displacement:

7.3 liters, 444 ci

Compression Ratio:

21.5 : 1

Bore:

4.11 inches

Stroke:

4.18 inches

Aspiration:

Naturally aspirated or turbocharged. Turbocharged version available for 1993 and 1994 MY trucks only

Injection:

Indirect injection (IDI), mechanical injectors, Stanadyne rotary style injection pump

Valvetrain:

2 valves per cylinder, standard OHV, standard camshaft in block

Peak Horsepower:

185 hp @ 3,000 rpm (naturally aspirated)
190 hp @ 3,000 rpm (turbocharged)

Peak Torque:

338 lb-ft @ 1,400 rpm (naturally aspirated)
388 lb-ft @ 1,400 rpm (turbocharged)

 

6.9L IDI and 7.3L IDI Performance Options

Modern electronically controlled diesel engines are relatively easy to modify for significant performance increases. The IDI engines are limited in aftermarket support and there are few options available to improve performance. To squeeze the most out of a Ford IDI, the following modifications are common:

Turbocharging - Aftermarket turbocharger kits are available for both the 6.9L and 7.3L IDI. Turbocharger systems designed for direct injection engines cannot be easily adapted, since the IDI has a high compression ratio and maximum boost needs to reflect the operational characteristics specific to an IDI. When retrofitting an IDI with a turbocharger, there are companies that manufacturer injectors and injection pumps designed to work efficiently with these systems. Performance injectors and injection pump upgrades are not available for naturally aspirated IDI engines. Airflow needs to be increased for these engines to accept fuel system upgrades without EGT (exhaust gas temperature) concerns.

Turning up the injection pump - The Stanadyne injection pump found on the 6.9L and 7.3L IDI can be turned up to flow more fuel. When done in moderation, owners will notice a moderate performance increase with minimal reliability concerns. For safety reasons, a pyrometer is recommended when turning up the injection pump. A pyro will also help you find the "sweet spot", where performance is maximized while maintaining reasonable exhaust gas temperatures under load.

Removing the soup bowl - From the factory, most 6.9L and 7.3L IDI engines have a restrictive bowl attached to the bottom of the air cleaner lid. The purpose of this "soup bowl" (as it is commonly referred to) is to reduce intake noise. It can be cut off and removed to marginally increase airflow to the engine, though a noticeable amount of intake noise will be present.

Free flowing exhaust - A custom exhaust system for an IDI will provide noticeable performance increases. The availability of pre-formed kits is limited, but having an exhaust shop fabricate a complete exhaust system with a straight through muffler is a viable option.