If you’ve been following along the last three months, you’ll know we added head studs, hybrid injectors, and custom tuning to our ’97 F-350 in the May issue, replaced its up-pipes in June, and added a bulletproof transmission last month. Our recent series of 7.3L upgrades and repairs was all part of taking the next step in making horsepower—and eliminating weak links. Head studs were installed to keep our head gaskets safe, the up-pipes were replaced to rule out exhaust leaks, custom tuning was required to efficiently fire the hybrid injectors, and a fortified E4OD was bolted in and given the task of harnessing the newfound power.
This month, we’re breaking down the anatomy of a hybrid Power Stroke injector. We’ll detail how it’s made, why it’s efficient for your engine, and what our 238cc, 80-percent-larger-nozzle hybrid is capable of flowing. In addition, we’ll showcase how custom tuning can keep a 7.3L’s stock bottom end in the safe zone, and how much horsepower we picked up on the dyno. But most of all, we’ll convince you why hybrids are the new entry-level injector for 7.3L Power Stroke fans.
1. 16mm intensifier piston (stock)
2. 7.1mm-diameter plunger and barrel (vs. 6mm stock)
238/80 Hybrid: Explained and Flowed
The 238/80 hybrid gets its name for flowing a maximum of 238 cc of fuel per 1,000 shots, and for its utilization of a nozzle capable of providing 80 percent more flow than a factory nozzle. This means that not only is a higher maximum amount of fuel delivered per combustion cycle, but it’s delivered faster (check out our injector flowchart to see its faster injection rates in action).
It’s important to know that the injectors in International’s T444E (7.3L), DT466E, and I530E all share the same dimensions, which is why parts can be interchanged and I530E injector components are used to create a hybrid. Our 238/80 injector, built by Unlimited Diesel Performance, starts out as an A-code injector (found in all T444E and 7.3L Power Stroke engines), and without the need for any machining is outfitted with a new, single-shot BD-code plunger and barrel (found in the I530E engine). This effectively increases the bore of the injector. The retention of the stock 16mm-diameter intensifier piston allows the hybrid to use less oil to actuate than a BD-code injector, and in this particular configuration it has almost the same capacity as a BD-code injector. This saves you money in the long run because a healthy ’99½ to ’03 OE high-pressure oil pump (or an Adrenaline high-pressure oil pump, in our case) is sufficient in supporting its oil demand.
*A pump in good overall health can hold 2,500 to 3,000 psi of injection control pressure (ICP) under wide-open throttle with this particular hybrid injector.
All of Unlimited Diesel Performance’s 80-percent nozzles (and its 100-percent nozzles, which are popular as well) start out as blanks and are electronic-discharge machined (EDM) to achieve the desired hole size. Its nozzles retain the stock seven-hole design, but each hole on its 80-percent nozzles measures 0.0075 inch in diameter (making it a 7x7.5 nozzle versus 7x6 stock). From there, its nozzles are Extrude-Honed for a perfect orifice surface finish (the 100-percent nozzles undergo slightly more Extrude-Hone work).
Flow Bench Tested:
Once built, all injectors are tested on Unlimited’s HEUI flow bench, which consists of a hydraulic pump to actuate the injectors, a gauge to monitor injection control pressure, and an AirDog fuel system for fuel supply. Four injectors are tested at a time. First, they’re run at full-throttle to purge all air, then they undergo several tests with varying injection control pressures (high-pressure oil). All injectors are balanced across the board during the flow test, and every unit flows within 2 to 3 cc of each other before being shipped.
Gearhead Automotive Performance Tuning
Using Power Hungry Performance’s 7.3L Power Stroke tuning software, Matt Robinson, owner of Gearhead Automotive Performance, created six custom files for us via a TS Performance six-position chip.
||Stock-like power, but with more horsepower than stock—without exceeding stock EGT limits
||1,100-rpm idle for cold-weather warm up
||Reduced engine noise for the drive-thru window
||Lower shift points than performance or tow tunes, 50 hp more than Heavy Tow tune
||Hot street performance with very little visible smoke
||Complete performance tune, but with great driveability and low smoke; also detuned slightly to keep boost less than 40 psi and drive pressure reasonable to extend turbo life
170cc Stock Nozzle (Stage I) Fuel Injectors
Stage 1 Flow Characteristics
We will note that comparing a Stage 1 injector to a Stage 3 hybrid injector is not an apples-to-apples comparison. However, in order to explain the benefits of the hybrid versus the Stage 1 (and Stage 2 for that matter), we are comparing them directly in terms of fuel per time. Both injector flowcharts display how many cc of fuel are delivered given a certain engine speed, pulse width (how long the injector is open), and injection control pressure (ICP).
Making power with any diesel engine is dependent on fuel per time (also referred to as injection rate, or cc per millisecond). The faster the injection rate is, the more fuel gets delivered in the usable injection window. With a stock 7.3L piston and factory spray angle, this usable injection window (or interval to hit the fuel bowl) is roughly 24 degrees before and after top dead center (TDC). Because our Stage 1 injector utilized stock nozzles, its injection rate was slower. A slower injection rate meant an earlier start of injection (increased injection timing)—commanded via tuning—was required to get as much fuel as possible into the cylinder within the usable injection window.
As you can see, it took 4 milliseconds of pulse width (injector on-time) and 3,000 psi of ICP before its maximum of 170 cc was flowed. When compared to the hybrid, it can achieve maximum flow (238 cc) at 3.5 milliseconds of pulse width—not to mention at a lower ICP (2,500 psi).
238cc 80% Nozzle Hybrid Fuel Injectors
Stage 3 Hybrid 238/80 Flow Characteristics
Looking at the hybrid’s flowchart, you’ll see its injection rate is much faster, thanks to the 80-percent-over nozzles. Basically, more fuel is delivered in-cylinder in a shorter time frame, and a lot less timing is required (that means less cylinder pressure and less heat). In addition, the quicker nozzle leads to a more efficient combustion process, so more fuel is burned. This means no unnecessary smoke and reduced exhaust gas temperature throughout the powerband when compared to the same horsepower output of the Stage 1 injector.
Across the board, the hybrids deliver at least 30 percent more fuel in the same injection window as the Stage 1s. For example, with 1.9 milliseconds of pulse width (PW) and 2,000 psi of injection control pressure (ICP), 105 cc of fuel is being flowed, whereas the Stage 1s were flowing 70 cc of fuel.
As mentioned, it only takes 3.5 milliseconds of pulse width and 2,500 psi of ICP, and the hybrids are flowing their maximum (238 cc). This also proves the hybrids don’t require more oil to operate effectively (once again, a healthy, single high-pressure oil pump will suffice).