skip to content
Driving Line Mark Logo

Bigger Is Better: Why It's Important to Upsize Diesel Fuel System Mods

When it comes to adding performance in modern diesel engines, it pays to go with big fuel injectors. Larger injector nozzles and higher fuel flow equals more horsepower potential while also making life easier for the engine. On top of that, oversizing your injection system can provide you with room for future horsepower growth, should your power goals increase some time down the road… Without a doubt, going big on the injector side of a diesel engine’s fueling combination gives you the best of all worlds. Being that they can be detuned for cleanliness, drivability and even horsepower limiting, there is literally no downside—hence the booming performance injector segment in the diesel racing industry.

Megatron Dodge Cummins Diesel Truck Pulling on Nitto Mud Grappler Tires

To be sure, a solid supporting cast of parts needs to be along for the ride when it comes to big diesel injectors, but with the right pieces in place the performance potential is endless. Below, we’ll present a fueling recipe that many of the fastest, most powerful vehicles in the diesel world are using.

Power And Reliability: Why Big Injectors Are All The Rage

Cummins 24-Valve Diesel Fuel Injector

Fuel injector technology has been behind some of the biggest breakthroughs in the diesel industry in recent years. In the high-horsepower realm, one key ingredient has been injectors fitted with very large orifice nozzles. Often referred to by the percentage they outflow the stock units (i.e. 400-percent over or 500-percent over), common-rail injectors equipped with these high-flowing nozzles not only facilitate huge horsepower, but also require very little duration (also known as “pulse width” or “injector on time”) to make big power. This means less heat and reduced stress for the engine to have to cope with—without sacrificing horsepower. For a typical 400 to 500-percent over injector, just 1,400 microseconds of duration is usually required to hit the engine’s target power level. In comparison, twice as much duration would have to be commanded for a stock size nozzle to realize substantial horsepower gains.

Bigger Injectors Are Quicker-Firing Injectors

Diesel Fuel Injector Nozzle

The key to “bigger injectors” is more than simply higher fuel volume. Thanks to larger nozzles and the appropriate injector body work, the added fuel can be injected quicker. This means less timing advance (i.e. start of injection) to achieve your power goals, which translates into less stress placed on the engine’s rotating assembly. Electrical discharge machining (EDM) is the most common means of enlarging the holes in a fuel injector nozzle. A high-voltage electric current, combined with a very fine electrode, allows for precise, equally-sized holes. It’s important to remember that, while larger nozzles can lead to increased horsepower, not all injectors (and nozzles) are created the same. Simply swapping a higher flowing set of nozzles onto an injector without increasing the injector’s needle lift will keep you from seeing the kinds of performance gains that could be realized should you send the injectors off to a reputable injection shop for flow testing, balancing and—as has already been mentioned—the appropriate internal body work.

Injector Body Mods

Common-Rail Diesel Fuel Injector internals

In order to support massive nozzles, what are known as internal body modifications have to be performed. Kept proprietary for obvious reasons, the big names in the diesel game perform a series of improvements that are necessary to get the most performance out of a given nozzle size. According to S&S Diesel Motorsport, internal body mods have to be performed in order to decrease fuel pressure at the top of the injector, which has to be done to make the most of the high flow rate of the nozzle. Body mods are also required because a race-style nozzle results in less pressure being present in the SAC region to lift the needle off of its seat.

Maintaining Rail Pressure: High-Flow High-Pressure Fuel Pumps

SS Diesel Motorsport Bosch CP3

To properly support a competition-killing set of diesel fuel injectors, the high-pressure fuel pump has to be up to the task of maintaining rail pressure. When low injector duration is commanded, life is made easier on the high-pressure pump. Even so, most competitors go overkill here to provide added insurance. The most common type of common-rail high-pressure fuel pump in the diesel performance market is the Bosch CP3, which was offered on the ’03-’18 5.9L and 6.7L Cummins and ’01-’10 6.6L Duramax. A 14mm stroker version from S&S is shown here (the stroke of an OEM CP3 is roughly 8mm), which is capable of supporting more than 1,400 hp.

Dual CP3’s And Beyond

Duramax Diesel CP3 High Pressure Fuel Pumps

Back before stroker high-pressure fuel pumps were available, diesel drag racers, truck pullers and dyno slayers relied on multiple factory displacement CP3’s to maintain the rail pressure their mega-sized injectors needed in order to perform optimally. Dual CP3 systems still survive today and remain appealing due to their ability to share the workload of producing injection pressures in excess of 26,000 psi. In wilder setups, triple, quadruple and even quintuple CP3’s have been tried (with great success) in supporting big horsepower efforts—like more than 2,000 ponies.

The CP4.2 (It’s Not All Gloom And Doom)

CP4.2 Diesel Injection Pump

Despite its reputation for failure on 6.6L LML Duramax engines (’11-’16 model year GM trucks), the Bosch CP4.2 platform has proven capable of supporting substantial horsepower—especially in Ford’s 6.7L Power Stroke. Combined with the quick-firing nature of piezo electric common-rail injectors, a 10mm CP4.2 aboard an ’11-present Super Duty—such as the version from Exergy Performance, shown above—can easily support north of 800rwhp.

Supporting The High-Pressure Pump(s)

FASS Diesel Lift Pump System

While the high-pressure fuel pump has to be sized right in order to support the injectors, the same thing has to happen on the low-pressure side of the equation. Getting adequate fuel supply from the tank to the high-pressure fuel pump is a vital part of the horsepower-making puzzle. Without ample fuel volume and pressure, the high-pressure fuel pump cannot maintain the rail for the injectors to draw fuel from. Chassis-mounted electric lift pump systems from FASS, AirDog and Fuelab are mainstay, all-inclusive products in this arena, with pumps capable of flowing more than 200-gph through ½-inch fuel lines.

Mechanical Lift Pumps

SP3000 Gear Driven Diesel Fuel Lift Pump

On the extreme side of diesel lift pumps, you’ll find gear-driven units such as the SP3000 from S&S Diesel Motorsport. This pump is a bolt-on solution that replaces the factory supply pump and can flow up to an incredible 3,000 liters per hour. The mechanical SP3000 can also produce up to 400-psi. When combined with S&S’s regulated filter head, it can support horsepower levels of 3,000 hp or more. Some of the nastiest common-rail diesel engines in existence are running this little pump.

For a look at injection pumps capable of supporting 2,000hp, 3,000hp and beyond, look no further than these radical setups.

  • For a look at injection pumps capable of supporting 2,000hp, 3,000hp and beyond, look no further than these radical setups.
Return to beginning of article

Recommended For You

Loading ...