7.3L Hybrid Injectors

- December 14, 2012

Building Power With Hand-Built Injectors If you are serious about diesel performance, replacing the stock fuel injectors with high-performance injectors should be a consideration. We’re looking to push 400 rear wheel horsepower with Project 7.3, so an injector upgrade, along with our other modifications, is a must. Fortunately, Unlimited Diesel Performance, in Bremen, Ohio, specializes in high-performance fuel injection, and much of the company’s expertise and reputation was built around delivering 7.3 Power Stroke fuel injection applications.

That fuel injection expertise is really what sold us on having Unlimited Diesel Performance handle the mechanical work on our 2000 Super Duty. On our first trip to the shop, Nate Bailor gave us a tour of Unlimited Diesel’s injector room, which looks more like a medical facility than a diesel shop. Stainless steel work surfaces and sophisticated equipment, such as the large ultrasonic parts cleaner, allow Unlimited Diesel to custom build injectors to better-than-new condition.   Stage 3 Hybrids   Because we were after stout, streetable performance, Bailor recommended we go with the company’s Stage 3 250/100 Hybrid injectors for increased fuel flow. The factory 7.3 injectors are a split-shot design and have a 6mm plunger and barrel. Unlimited’s Stage 3 Hybrid design replaces that with a 7.1mm plunger and barrel used in the DT466E / I530E International engines. The Stage 3 design also converts the injector to a single shot to eliminate the small, high-pressure oil pressure drop experienced between the pre-injection and main shot, with the split-shot injector.

To accommodate the increased fuel flow, the Stage 3 Hybrids also increase the tip hole size from .006 inch to .0085 inch while retaining the factory, seven-hole spray pattern for best efficiency. The final selling point on the Unlimited Diesel injectors is the fact that they come with a limited lifetime warranty. As long as you return the warranty card with the injector cores and follow a regular oil change and maintenance schedule, Unlimited Diesel has you covered.   Dumping Fuel   Injector flow is determined by a mathematical equation that multiplies the surface area of the plunger diameter and stroke of the intensifier piston to come up with cubic millimeters , or [[mm3]]], and then each injector is fired 1,000 shots to measure cubic centimeters, or cc.

Our stock 7.3 injectors had a maximum flow rate of 140cc. The Stage 3 Unlimited Diesel Performance injectors flow 250cc, for an increase in displacement of 78 percent while using less high-pressure oil than the company’s stock AD injectors. Unlimited Diesel currently offers injectors ranging from mild to wild.

Unlimited Diesel currently offers every injector, from stock to 455cc, and everything from stock OE flow nozzles to 30, 80, 100, 200, 400, 600 and 800 percent increases in flow. Everything from 400 percent up is considered to be for competition use. Some truck owners are never satisfied, so Unlimited Diesel Performance is currently working on an injector that will dump up to 750cc of fuel for extreme pulling applications.   Building Better Injectors Since the stock injectors were already out of the Super Duty from last month’s headwork, Nate agreed to let [Diesel World] follow along and see some of the magic that happens in the injector operating room. We’ve detailed much of the procedure in photos and captions that illustrate this article, but they can only tell part of the story. Rebuilding or tricking out fuel injectors is a job best left to a professional. A good mechanic can do it, but one mistake can mean very expensive repair bills and more downtime.   Clean Is Mean   There are also some specialized tools involved. In addition to a parts washer with a 3 micron filter, Unlimited Diesel takes things one step further and treats the components to a spa treatment in its Pro Ultrasonic cleaning tank. The Ultrasonic uses a combination of 175 degree (F) water and an alkaline-based detergent with rust inhibitor to sanitize the parts with the magic of ultrasonic waves or pulses. The parts that come out of the tank at the end of the process literally look better than new.

Disassembly and rebuild of the injectors also require a few tools that you won’t find in many mechanics’ toolboxes. To safely remove the nozzle nut without damage, for example, Unlimited Diesel uses a special, socket-like fixture that grips the nut and applies pressure evenly without the risk of damaging it. There’s also a special alignment tool that keeps everything true and straight when torqueing down the adapter plate to the body of the injector.   Trouble Shooting   Inspection of the individual components during tear-down and after cleaning is a critical step. Dirty oil, for example, can score critical surfaces inside the oil side of the injector. The poppet valve is particularly susceptible to wear from dirty oil. Fuel can also leave deposits that hurt performance and can lead to wear. One of the most critical tolerances inside the injector is between the adapter plate and the armature. It shouldn’t be less than .002 inch, or 0.05mm.

Unlimited Diesel also bench tests the solenoid by running a resistance test with a multimeter before assembly. Resistance should be around 3.2 to 3.4 ohms. Once assembled, the company also bench tests the psi required to pop the injector open to make sure it is functioning properly before installing in the truck. For this application, it should be 2,750 psi.   The Build   With all the cleaned and replacement parts at hand on the bench, the assembly starts with the body clamped in the bench vise with the solenoid side down. We won’t go into a detailed description here, because there are a ton of steps to the process. Essentially, the various components inside the injector body stack from the solenoid end to the tip. Many are aligned with dowel pins, while others are fastened with machine screws.

The 7.1mm plunger-and-barrel assembly and higher-flow nozzle are the keys to the Hybrid injector build. Unlimited Diesel uses other “tricks” to make its custom injectors unique. Understandably, the company didn’t share all its trade secrets. One item Nate insists on is the highest quality O-rings he can find. He prefers to only use Alliant Power External O-rings.

As you might imagine, proper fastener torque is critical during reassembly. Many of the torque settings inside the injector are measured in inch/pounds. He also uses a torque screwdriver set to just 13 inch/pounds for the armature screw. The big nozzle nut that holds everything together is torqued to 75 pound/feet with that expensive fixture we talked about earlier.   Go With the Flow   The final test of the new injectors is to check the proper and matched flow on the flow bench. Unlimited Diesel Performance built its own flow bench to closely replicate real-world conditions in the truck. It uses actual fuel and oil, rather than the calibrating fluid some benches use.

Utilizing a factory Ford IDM (injector driver module), Unlimited Diesel made the voltage input adjustable so that different model years, as well as competition injectors, can be tested. The flow bench can run at 100, 110, 120 and 140 volts.

Our Stage 3 Hybrid injectors flowed perfectly at both idle and high rpm. Max flow was exactly 250cc, with all collection beakers filling to identical levels.   Installation   Installing the Stage 3 Hybrid injectors is a simple matter of popping off the valve covers, lining up the injector in the head and pushing it down into the bore. The new injectors with fresh O-rings were a nice, snug fit in the new injector cups we installed in the last [[DW]] issue.

The final step is to install the injector hold-down bolt and oil deflector. The torque on these two bolts is 140 inch/pounds. It is important to remember to connect the injector harness wires to the connectors on the solenoids before reinstalling the valve covers.

We can’t wait to fire up Project 7.3 and see how the Unlimited Diesel Performance Hybrid injectors perform. Unfortunately, that will have to wait until we make the rest of the under-hood performance modifications and slide the engine back into the Super Duty.

The waiting is the hardest part.


AMSOIL 800.956.5695 www.amsoil.com

ARP 800.826.3045 www.arp-bolts.com

Bob Boyd Ford 740.654.1122 http://bobboydford.com

Smith Bros. Pushrods 800.367.1533 www.pushrods.net

Unlimited Diesel Performance 740.569.1319 www.unlimiteddiesel.com

Whitaker Tools 270.465.0212 www.whitakertools.com

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