Common-Rail Injector Tech - Diesel World

The Past, Present, and Future of Diesel Performance

When high-pressure common-rail debuted on the LB7 Duramax back in 2001, it changed the way we look at diesels. Ultra-high injection pressure, solenoid-style, multiple-event injectors, and full electronic control over the system brought the most refined diesel performance we’d ever seen to the table—along with quieter, cleaner engine operation. When Cummins hopped on the common-rail bandwagon in 2003, the result was the quietest, cleanest-burning, and most powerful 5.9L it had ever produced. But once the aftermarket got ahold of electronically-controlled high-pressure common-rail, its true untapped potential was realized. Through ECM tuning alone, another 200-250 hp could be added to a truck’s bottom line, thanks in large part to the factory injectors and high-pressure fuel pump being capable of supporting it. Then it was time to find out what a modified common-rail injector could do, which consequently opened up a whole new world.

Today, common-rail dominates the landscape—be it on the street, the dyno, or the track—so it stands to reason why so many aftermarket companies are building larger injectors for them. From 15-percent over stock to 500-percent over stock and beyond, there is an injector for everyone’s needs. But how do you know exactly what you’re getting when you buy aftermarket injectors? To answer that question, we consulted some of the biggest names in the diesel industry: Dynomite Diesel Products, Exergy Performance, RCD Performance, and S&S Diesel Motorsport. From nozzle modifications to internal body work, to spelling out the difference between solenoid and piezo injectors, to helping us understand a flow data sheet, this is what they had to say.

High-pressure common-rail injectors

High-pressure common-rail injectors are almost single-handedly responsible for keeping the diesel engine alive in today’s stringent-emissions world. From left to right, you can see every make and model injector the common-rail experts at S&S Diesel Motorsport specialize in: BMW M57 (piezo), 6.4L Power Stroke (piezo), ’11-’19 6.7L Power Stroke (piezo), ’20 6.7L Power Stroke (piezo), LB7 Duramax SAC00 (solenoid), LLY Duramax (solenoid), LBZ Duramax (solenoid), LMM Duramax (solenoid), LML Duramax (piezo), L5P Duramax (solenoid), early 5.9L Cummins (solenoid), late 5.9L Cummins (solenoid), ’07.5-’18 6.7L Cummins (solenoid), and ’19-present 6.7L Cummins (solenoid).

Common-rail Solenoid Injectors

In the world of common-rail diesel injectors, there are two types: solenoid and piezo (the solenoid type is shown here). The former type features two pressure chambers and is energized via its solenoid, which takes its orders from the ECM. Found in ’01-’10 Duramax engine, ’17-present Duramax’s, and ’03-current Cummins power plants, the solenoid injector is the most commonly used (and modified) in the industry.

LML Duramax 6.& L Power Stroke piezo injectors

As for piezo injectors (found in the LML Duramax and 6.7L Power Stroke), piezo crystals are energized by a quick electric pulse, and the injector opens faster than its solenoid-type rival. However, while piezo injectors are quicker to fire (open), they are slower to close (end of injection). In time and with more market demand, piezo technology may progress like it has for the solenoid style units.

Injector Nozzle

The most common upgrade for a common-rail injector is the installment of a larger, higher-flowing nozzle. The most common method of opening up the holes in the nozzle is through the process of electrical discharge machining (EDM). It’s performed using a high-voltage electric current, combined with a fine electrode, and is well-known for its accuracy—something that’s vitally important when precise (and equal) amounts of fluid need to flow through a component.

AFM Treated Diesel Injector Nozzle

After its injector nozzles have passed through the EDM process at S&S Diesel Motorsport, each unit is treated to Abrasive Flow Machining (AFM). This forces an abrasive media through the nozzle under extreme pressure, and during the process it removes unwanted material from the walls of the nozzle (as well as enlarging and finishing the nozzle’s passages).

Injector Nozzle Spray Pattern

As you might’ve imagined, not all injector nozzles are equal. In fact, a nozzle’s hole count and positioning, flow rate, and spray angle all form its combustion recipe. From the factory, each engine has its own spray pattern designed to work in perfect harmony with the fuel bowl in the piston below it. In competition applications, spray angle can make or break the performance of any engine.

Diesel Injector Bodies and Components

At a certain point (or rather a certain nozzle size), modifications have to take place within the injector body itself. Much of this work is understandably kept proprietary, but the folks at S&S Diesel Motorsport did divulge a couple things. 1. That body modifications are necessary because a competition-sized nozzle will lead to less pressure being present in the SAC area to lift the needle off of its seat, and 2) Pressure at the top of the injector has to be decreased in order to utilize the high flow rate of the nozzle.

Injector Calibration Summary

Any reputable injector builder will include a flow chart or data sheet with its injectors disclosing their flow capabilities, efficiency, and how closely balanced they are to each other. Exergy Performance calls theirs a calibration summary, and as you can see it’s quite comprehensive. The chart lists the test points employed and the performance of each injector during testing. This particular chart represents the results of testing a set of piezo injectors equipped with 60-percent over nozzles for a 6.7L Power Stroke.

Injector Calibration Summary with Nozzle Flow

On this calibration summary, also from Exergy and derived from testing a set of 60-percent over piezo injectors intended for an LML Duramax, you can see the nozzle flow measurement of 1,370 ml/min. The nozzle flow measurement is obtained on a flow bench using Viscor 1487 AW/2 calibration fluid (SAE J967), and at a preset pressure (100 bar) and constant temperature (40 degrees C). All of Exergy’s nozzles are balanced within 1-percent of each other

injector duration chart

The test point for an injector consists of a specific rail pressure and pulse width (also known as injector duration, or injector on-time). However, it’s important to note that different types of injectors operate at different rail pressures and pulse widths. The test points shown here are typical for a modified piezo injector in an LML Duramax.

rail pressures and pulse widths

Injector output data is measured at different rail pressures and pulse widths. As you can see here, one of Exergy’s 60-percent over LML injector’s peak flow at 180 MPa (roughly 26,000 psi) and 2,000 microseconds of pulse width (µSec representing microseconds) is 290mm3. Regardless of injector output and nozzle flow numbers, it’s important to remember that each of the injector builders mentioned in this article are currently at the top of their game, with all three having various customers producing north of 2,000 hp.

Injector shot-to-shot stability

Exergy measures the shot-to-shot stability of its injectors, and displays it as a percentage, in order to catch any internal injector problems. If microscopic debris, varnishing, or wear is present within an injector it can cause each individual shot of fuel to be vastly different from one to the other.

Backflow data on an injector calibration summary

The backflow data on an injector calibration summary is the return flow of each injector, measured in ml/min. The 20 ml/min number you see here is on the low end of the 20 to 22 ml/min average most LML injectors see at rated power. Thanks to the extremely low backflow of common-rail injectors as compared to the injectors of old, a smaller displacement injection pump can be used to obtain the performance you’re after.

Injector balance spread chart

This section of data provided from Exergy represents the balance spread between the injectors at the set mid-point and high-point fuel quantities. At the high test point of 180 MPa rail pressure and 2,000 microseconds of pulse width the spread is 2.03 percent. At the lower pulse width test point of 1,000 microseconds, the spread is less than that. Exergy’s injectors are always balanced within a 4-percent spread, but are usually tighter than that, as is evident here.

Used Diesel Injector

To avoid having to change injector quantity adjustment (IQA) codes, it’s always wise to label your injectors based on the cylinder number they were removed from before sending them in to be modified. Exergy will also take the extra step of cataloging each injector’s serial number (provided it’s still visible) for future reference and troubleshooting.

Diesel Injector Testing Equipment

Make no mistake, there is much more to an aftermarket injector than flow numbers. The testing equipment that’s employed is also used to verify correct solenoid operation, run leak tests, and perform baseline testing on core units received. You can see some of the state-of-the-art testing equipment employed at S&S Diesel Motorsport’s facility in this photo.

Diesel Injector Bodies with Nozzles

Have you ever wondered why an injector builder would rather sell you a complete set of performance units rather than just simply ship you a set of nozzles? One big reason is needle lift, which needs to be matched to the nozzle. By throwing a set of higher flowing nozzles on stock bodies without increasing needle lift, you won’t be able to utilize the full flow potential of the larger nozzles. In addition to making sure you’re getting full fuel flow (what you’re paying for), a reputable builder will want to make sure you get a balanced set of injectors.

S&S Diesel Motorsports Ram CP3

With the birth of higher flowing injectors came the need to maintain rail pressure. In the early days, that meant adding a second (stock displacement) high-pressure fuel pump to your Duramax, Cummins, or Power Stroke. However, in recent years stroker pump technology has made huge strides. Whereas a dual CP3 kit used to be the go-to option for a 1,000hp build, a single 12mm CP3 can easily meet the end-user’s needs today. And thanks to all the R&D that’s been poured into these large displacement pumps from companies like Exergy Performance and S&S Diesel Motorsport, reliability and longevity aren’t a concern.

10mm, 12mm, and 14mm nomenclature stems

The 10mm, 12mm, and 14mm nomenclature stems from the stroke of the high-pressure fuel pump’s camshaft. The camshaft is what drives the buckets within their respective plunger bores. With increased stroke, the buckets have to be modified or redesigned completely. In its 10mm CP3 pumps, S&S Diesel Motorsport uses a modified version of the factory bucket (left), while a completely redesigned version is used in its 12mm and 14mm pumps.

CP4 pump with CP4 input shaft

While the Bosch CP3 is the pump of choice for high horsepower applications, big advancements have been made with the Bosch CP4.2 platform in recent years. The twin piston pump has been utilized on Ford’s 6.7L Power Stroke since its inception, the ’11-’16 LML Duramax, and is now present on ’19-newer 6.7L Cummins mills. For an owner of either of these late-model engines looking for 650 to 850 hp, the stroker versions of the CP4.2 offered by Exergy Performance and RCD Performance are a hit. Exergy’s 10mm CP4.2 supports north of 800-rwhp and RCD’s Thumper pump—which features a 10.3mm stroke and displaces 33-percent more fuel than the stock ’15-’17 6.7L Ford CP4.2—supports the same.

5.9L Cummins Fuel System Planner

To help the novice piece together the perfect fuel system to meet his or her horsepower goal, S&S Diesel Motorsport offers invaluable charts on its website. These fuel system planners show you the injector nozzle size and CP3(s) you’ll need in order to make as little as 500 hp or as much as 2,700 hp. The version shown here applies to the 5.9L Cummins common-rail. Notice that its single 10mm CP3 can handle everything a set of its 80-percent over injectors can throw at it, which is a popular combo for street-driven trucks in the 750 to 800 hp range. By comparison, and due to higher-flowing factory injectors (as well as the fuel rail), the same power level can be achieved with a set of 45-percent over injectors and 10mm CP3 in the 6.7L Cummins application.

Exergy Performance Billet Dual-Feed 6.7L Cummins Rail

In support of dual high-pressure fuel pump configurations, Exergy Performance manufactures a billet, dual-feed 6.7L Cummins rail. It provides a 10-percent increase in volume over the factory 6.7L rail, offers an additional feed provision for your second pump, and also houses the desirable single stage pressure relief valve. Its billet rails can be had with or without a 2,000 bar sensor and 2,200 bar single stage pressure relief valve.

S&S Diesel Motorsports Pressure Relief Valves

S&S offers several pressure relief valves shimmed to open at a higher pressure than stock (we’ll also note that the company never recommends running a rail plug). Sudden surges and spikes in rail pressure occur when a driver lifts off of the throttle, and a functioning pressure relief valve is vital to vent the excess pressure. S&S also recommends its customers use a pressure relief valve that’s shimmed to open 200 bar (2,900 psi) beyond what the maximum commanded rail pressure is. The company’s single stage pressure relief valves for the 5.9L Cummins, LB7 Duramax, and LLY Duramax are pictured here.


It’s important to remember that, while increasing rail pressure beyond OEM specs is an easy way to make more horsepower, the added pressure is harder on injectors. In S&S Diesel Motorsport’s experience, the further you go past the factory pressure rating, the quicker the injectors wear out. Another consequence of exceeding the OEM rating is excessive leakage (return flow), which increases rapidly until the high-pressure fuel pump(s) can no longer keep up or the injectors are damaged. Excessive rail pressure should be reserved for competition purposes, where injector longevity isn’t as paramount as it is in a daily driven vehicle.

ACDelco Fuel Filter

Tighter tolerances and components that depend on ultra-high pressure to function properly makes contaminants like corrosion, debris, and water absolutely unendurable for a common-rail system. Your best defense against contamination is to always keep high-quality, clean fuel in the tank, ensure that water never infiltrates the fuel system, and make certain you observe proper fuel filter change intervals. Last but not least, practice extreme cleanliness when replacing any fuel system components.


Industrial Injection

Exergy Performance

RCD Performance

S&S Diesel Motorsport