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

With modern diesel engines, there’s a potential to achieve impressive horsepower gains by going bigger with the fuel system, especially with the injectors. Further downstream, larger fuel flow from the injectors achieves greater power, enhanced efficiency, and less wear and tear on crucial components. This is important whether your end goal is a street driven powerhouse or a race truck, since starting with large injectors enables more flexibility and exposes a broader performance ceiling.

Let us delve deeper into the reasoning behind why making fueling modifications to achieve greater efficiency translates to increased horsepower.

Why Big Injectors Are All the Rage: Power and Reliability

There have been significant improvements in injector design and fuel delivery in recent years, with high-flow injectors taking the lead. These injectors enable massive power gains with shorter injection durations due to their increased flow. It’s common to see high-flow injectors labeled by how much overstock fuel they flow, e.g. 400% over.

Take for instance a 500 over injector with the capability to hit power numbers with only a 1,400 microsecond duration. A stock injector would require double that which increases cylinder temperatures and adds wear and tear. The less the injector is at work, the cooler the engine operates, leading to a longer lifespan.

Fatter Injectors Burn Cleaner and Faster

Bigger injectors do more than provide extra fuel—they provide it at a greater flow rate. With increased fuel flow rates, injection timing can be set conservatively. Less timing advance also reduces the stress placed upon the crankshaft, piston, and connecting rods.

Most big name performance fuel injectors are made with milling techniques which use electrical discharge machining (EDM). These are in extreme precision trim work on nozzles, but precision trims aren’t everything and oversized nozzles require modifications to the cartridge for balance to achieve peak results. Without proper needle lift and flow balancing, no matter how big an upgrade will be installed in the form of nozzles, the maximum benefits will not be attained.

Internal Body Mod For Injector Bodies

Internal body modifications are needed to take advantage of the race-style high flow nozzles. These modifications, which most shops won’t advertise publicly do involve elements where pressure above the needle is decreased while flow within the SAC region is enhanced.

People like those from S&S Diesel Motorsport focus on this type of internal optimization. The modifications enable the injector to better support the performance while maintaining reliability, atomization quality, and balance.

Maintaining Rail Pressure: The Balance High Flow High Pressure Fuel Pumps

With Bigger injectors, the high-pressure pump has to provide fuel at a faster pace. Even though short injector duration puts the load on the high-pressure side, there is still a need for overkill in this region for almost all high horsepower builds.

A good illustration is the 14mm stroker CP3 from S&S which can support over 1400 hp and more than doubles the output of a stock CP3. The CP3 is a staple performance part, originally found on the Duramax and Cummins engines.

Dual, Triple, Quad CP3 Systems

Prior to the availability of large-stroke pumps, multi-pump CP3 setups were a popular choice for diesel racers. To this day, dual setups remain popular and are extremely reliable in maintaining rail pressure under harsh conditions.

To support performance builds exceeding 2000 hp, triple, quad, and even five pump setups have been implemented and proven to be effective. These configurations in diesel performance prove that “too much” fuel is never a negative thing.

CP4.2: Underrated but Able

The CP4.2 is a mixed bag when it comes to reputation, especially among 6.6L LML Duramax owners, but it can be made to perform exceptionally with the right parts. A case example would be Ford’s 6.7L powerstroke which does well with upgraded 10mm CP4.2s and piezo injectors.

Exergy Performance supplies one that with the proper supporting mods can exceed 800+ rwhp easily. Controversial as some pumps may be, they can perform exceptionally when paired with the right components.

Don't Forget the Lift Pump

As any high-flow injection system, the supply determines flow. Electric lift pump systems from FASS guarantee constant fuel delivery from the tank to the high-pressure pump. Many kits come with ½ inch lines and boast over 200 GPH flow rates.

These systems are important for maintaining the pressure and preventing fuel starvation during high load.

Mechanical Lift Pumps: Extreme Flow for Extreme Power

For serious builds, gear driven mechanical lift pumps take supply to the next level – S&S SP3000, for example. They’re built for race level fueling demands with flow ratings up to 3,000 LPH and pressures as high as 400 psi.

Rigged with a regulated filter head, the SP3000 alone can support over 3000 hp builds proving that when it comes to diesel fuel systems, bigger is better.

Final Thoughts

As with everything, there is a limit. Oversized components like diesel fuel system parts and injectors fuel more than just power. It enables greater control, improved efficiency, and prepares the vehicle for future enhancements. When tuned correctly, large injectors with shorter duration, less timing advance, and cooler operation can actually be gentler on the engine.

If you pair your injectors with the appropriate body mods, high-pressure pump, and lift pump system, you'll have a formula for powerful and clean performance both now and in the future.