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Diesel Tech Q&A: Improving Airflow

Originally Published in Trailer Life Magazine

APRIL 2020
Improving Airflow

Red letter QI’ve been thinking of going to a K&N filter or filter-charger system on my 2018 Ram 2500. I’ve been told not to do this. I’ve used the aftermarket air-filtration systems on my gas vehicles before and was happy. Pros and cons on doing this with my diesel?
Norm Ott

Green letter AAll internal-combustion engines, gas or diesel, derive some level of benefit when airflow is improved. An engine is just a sophisticated air pump; the easier it is to move air in and out, the more efficiently it performs. How much better an aftermarket air-filter system is than OEM is debatable. A 50 percent improvement in airflow over OEM doesn’t equate to 50 percent more power or a 50 percent improvement in fuel economy.

Diesels, such as the 6.7-liter Cummins in your Ram 2500, derive power from how much fuel is injected into the cylinders. Providing more airflow doesn’t automatically increase power unless you provide the engine with a way to add more fuel to match that improved airflow. However, what improved airflow does do in a turbo-diesel is enhance engine efficiency (i.e., fuel economy) because the turbo doesn’t have to work as hard sucking in air.

“Some people think that once airflow is increased, additional fuel must be added at all times,” says Gale Banks in an article on www.bankspower.com, “and that would hurt fuel mileage. This is not the case during normal driving. Increasing airflow means an engine doesn’t have to work as hard to overcome pumping losses. In other words, power that was previously consumed by pumping losses will be available to do work after airflow enhancements have been made. Or, looking at this from the economy standpoint, the same amount of work can now be done while consuming less power (fuel). So, in effect, what really happens is that, during normal driving, fuel consumption required to achieve equal acceleration or cruising speeds will be less than before the flow enhancements were made.”

If you read aftermarket air-intake and filter manufacturer advertisements closely, most never say the power gains are at peak, but rather at some spike low in the rpm during a dyno run when the turbo spun up faster than it would stock because of the higher airflow. They also use words such a “may” and “could” when it comes to improving performance.

What I’ve seen over the years watching dyno testing is aftermarket intake systems may provide 1 to 5 percent power gain over factory stock numbers. On a 350- to 450-horsepower diesel, that’s nothing you’ll notice underfoot. In mpg gains, it’s very difficult to say whether or not your Ram would gain 1, 2 or even .5 mpg. Far too many variables come into play to say what mpg gains come from day-to-day use.

The big question is how many miles would you have to drive to get the return on investment for the new air-intake system? If you drive 20,000 miles a year, and really did see a 2-mpg gain, that would save you 110 gallons of fuel.

Bottom Line: Shop around when it comes to air-intake systems. Read the fine print closely before you buy. They do improve efficiency, but by how much and at what cost? Not everyone is going to see or get the same improvements, even if the vehicles are identical.

Old Diesel, New Injectors

Red letter QI have owned a 1993 Ford F-350 Crew Cab long-wheelbase 4×4 ZF five-speed with the 7.3-liter IDIT (turbo) engine since it was almost new. Over the years I have traded out the Garrett (smoker) turbo for a Banks Sidewinder, installed a Hypermax intercooler, built custom pipes and tubing to make it work with the Banks turbo and resealed the top end. The injector pump is cranked up four flats, and timing is set at 8-degrees BTDC. The engine runs strong, but with 191,000 miles it needs the injectors replaced. Should I replace them with new or reman units? They are a unique part number for the IDIT.
Mark Alvarez

Green letter AWorn injectors, in general, contribute to a loss in fuel economy, hard starting, smoking and poor performance. With the old International 7.3-liter IDIT, the other concern with worn injectors is fuel dilution and fuel leaking into the cylinders and past the pistons while the engine is off, resulting in what is called a “dry start” condition that causes damage to the cylinder wall, or in worst-case scenario, a burned piston.

It sounds like you are planning on keeping your Super Duty for a while, so when it comes to the injectors, I suggest new instead of rebuilt or remanufactured replacements. Your particular engine (1993-1994 IDIT) uses Motorcraft CMR3RM G-code injectors, and a good source is Industrial Injection. Do not use injectors made for the non-turbo model IDI. If you want to go rebuilt to save a little money, I’d suggest checking out those offered by Dieselogic.

With the miles on your IDIT, you should also change the glow plugs and glow-plug wiring when the injector service is done. On all IDI diesel engines, use a fuel additive with every fill-up. These engines were engineered long before ULSD (ultra-low sulfur diesel) was mandated, so they were built to run on LSD (low-sulfur diesel).

Sulfur plays a pivotal role in the lubrication properties of diesel fuel. Hence, ULSD doesn’t provide sufficient lubricity to maximize the service life of injectors and the injection pump of these older diesels. Stanadyne makes a good additive that also provides a Cetane boost for a little better performance and easier starting in cold climates.

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Have a Diesel Tech Question?

To ask Bruce W. Smith a question about maintenance, repairs or upgrades to your diesel truck, SUV or van, go to the Diesel Tech Q&A home page, scroll down to the Leave a Reply box and type in your question. Please include your full name and hometown.

Bruce W. SmithA respected automotive and RV journalist and longtime Trailer Life contributor, Bruce W. Smith has held numerous editorial titles at automotive and boating magazines, and authored more than 1,000 articles, from tech to trailering. He considers his home state of Oregon a paradise for RVing and outdoor adventure.

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