Making more power by modifying an injector tip isn’t as easy as it might sound. It requires specialized machining to not only increase the size of the holes, but also to add several more holes, plus some intricate angles and spray patterns.

For details, we consulted with Dan Scheid of Scheid Diesel, who is well known for modifying pickups for sled-pullers, among many other high-performance applications with outputs as high as 2,800 horsepower. He also had a few pointers to share about upgrading street trucks as well.

Scheid’s injector assemblies are designed for high-flow, high-load applications. Made of chromoly with more material than a factory unit, they have more tensile strength and custom feed passages. At top is an IH type for a Navistar DT466. The lower unit is for a Cummins B-series.

For a fairly modest increase of around 100 to 300 horsepower, enlarging the orifices in an injector nozzle typically does the job. Typically, each nozzle hole on a factory injector measures about 007 inches, while the the largest holes done by Scheid can be as big as .039 inches. That’s more than five times as large. It could be compared to the difference between a drinking straw and a fire hose.

Of course, that maxed-out orifice is usually only for competition rigs. It’s at these much higher levels that things get way more complicated. As noted at the outset, besides increasing the size of the holes, other upgrades are needed, such as the number of holes, the spray pattern, and spray angle, along with various engine upgrades.

At left is a stock, IH injector body with a single feed. At right, additional fuel-feed holes are evident in a Scheid billet tri-feed injector body.

The number of holes can vary from five to eight on a factory injector to as many as 12 on a custom injector. Scheid increases fuel flow by not only enlarging hole size but also, in some applications, the number of holes. That’s because flow rates on a 2,800 horsepower sled-puller can run as high as 1600cc, representing as much as a 500 percent increase.

Enlarging and modifying the holes requires specialized tools. Scheid employs EDM (Electrical Discharge Machining, also called “burning”). Used extensively in the fine machining of complex forms and shapes in mold and diecutting, this device also handles fine-hole drilling in injector cups. It employs a thermal process (called a dielectric field) that removes and re-deposits material on the object being machined. The recast area is usually much harder than the original surface with more resistance to abrasion and corrosion.

Electrical Discharge Machining (EDM) is a very precise way to enlarge or add holes in an injector tip, and also change the spray pattern. Operating the EDM’s “burning” requires a flow of both deionized water and dielectric flushing fluid.

While some diesel performance shops rely exclusively on extrude honing to modify an injector nozzle, Scheid prefers EDM for maintaining precise spray angles and orifice sizing (with tolerances typically within two to four percent).

As for spray angles, that’s a science in itself, because where the fuel hits the piston top dramatically affects performance. “We don’t want the fuel to spray the cylinder walls,” Scheid explains. On the other hand, if the spray is too concentrated in the center, not enough diffusion takes place in the air/fuel mixture. “Ideally, we like to see the fuel spray hit right at the edges of the fuel cup,” he points out.

Piston configurations vary, so that’s only a general guideline. Aiming the spray properly is critical to hit “the sweet spot,” and depends on head porting, pump timing changes, and the piston cup’s configuration. For instance, a 12V Cummins has an offset cup, while the 24V is a center-cut, so the spray pattern must be adjusted accordingly.

This holding fixture with wire pins are for evaluating the spray angles, which form a funnel-shaped flow onto the piston, typically at 142 to 160 degrees for stock to mild applications.

“Generally, custom spray angles range from 130 to 160 degrees,” points out Scheid’s machine shop manager Todd Emmert, but he says this aspect demands another level of complexity.

So, those figures are only an approximation. “It depends on how a customer wants to use fuel with airflow improvements,” he adds. In other words, other variables are involved, allowing for an interaction between air, fuel, and performance parts to achieve an optimum trifecta for power delivery.

Overall, “Employing EDM allows us to focus on how to use air,” Emmert notes. “Our emphasis is on producing a broad band of horsepower, with a proportionality of upgrades. Nozzle improvements represent one tactic that’s part of a larger strategy of performance enhancements.”

As one example of a competition rig with extensive injector upgrades, Brad and Susie Ingram campaign a ’96 Ram 3500 that’s a champion sledpuller. Brad also happens to work for Scheid as well. Their truck has undergone many other changes since its first run down the track during the summer of 2001.

The mods start from the front with a custom weight box and built-in ice tank containing 120 pounds of ice, 10 gallons of water, four batteries, and several hundred pounds of steel weights. “It’s all about putting as much weight up front as possible,” Ingram points out. “The rear of the pickup is basically just an empty shell, with some tubular bracing for the rear end.”

Brad and Susie Ingram’s ’96 Ram 3500 is a champion sledpuller sponsored by Scheid, and has extensive injector upgrades.

The engine has a 6.7-liter Cummins block, one-inch steel deck plate, custom sleeves, Arias Pistons, billet connecting rods, billet steel roller camshaft, and a 6.7 crankshaft.

“We run a 12-valve, CNC-ported cylinder head with our D-shaped intake, and a T6 exhaust manifold,” Ingram adds. “The fuel system utilizes our billet triple-feed injectors, a 16 mm injection pump (PES6P1050401) capable of 1500 cc of fuel, and stainless steel .120 injector lines.” Flow rates on a 2800 horsepower sledpuller can hit 1600 cc, representing as much as a 500 percent increase.

Of course,  burning that much fuel requires massive airflow. “We run a twin-turbo set up with a 4,000 horsepower air-to-water cooler,” Ingram says. The turbos are Holset units with custom five-inch, billet compressor wheels. But just pushing in copious amounts of air isn’t sufficient — precision computer control is crucial at this extreme level of performance.

The sled puller runs a 6.7-liter Cummins with numerous internal upgrades. The fuel system utilizes billet triple-feed injectors, a 16mm injection pump (PES6P1050401) capable of 1500cc of fuel, and stainless steel .120 injector lines.

“Using a Corsa data logger, we can monitor temps, boost, exhaust, oil, fuel, and water-injection pressure of all six cylinders. Plus we can monitor throttle and axle travel, as well as ground speed, engine, clutch, and turbo speed. It also controls our backup water-injection system.” On just one pass, the Scheid rig gulps down a gallon of water, and a couple gallons of fuel, while melting 120 pounds of ice.

As for care and feeding of this behemoth, “We inspect the oil filter every pass, and change oil every three runs,” Brad relates. “We check miscellaneous bolts, clamps, etc. We rebuild the engine once per season just to inspect all internal components.” With this sort of meticulous attention, the block is able to run multiple seasons, but it all starts with those minute upgrades on the injector nozzles.