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2007.5–2018 6.7L Cummins Injector & CP3 Sizing Guide: How to Choose the Right Fuel System (Common Rail)

2007.5–2018 6.7L Cummins Injector & CP3 Sizing Guide: How to Choose the Right Fuel System (Common Rail)

Kevin Kubinak |

Looking to take your 2007.5–2018 6.7L Cummins to the next level? Whether you're chasing 600 horsepower or going all-in for 1200, this guide breaks down proven fuel and air combos to hit your power goals.

All the recipes below are based on real-world Full Send Diesel builds — using the same parts we sell and run ourselves.


Fuel & Air Recipes by Horsepower Target

600–700 HP

800–900 HP

900–1000 HP

1100–1200 HP

Note: These recipes are proven, but keep in mind there isn’t one specific way to make horsepower. There are multiple different fuel and air options that will also work to achieve your goals. This is just what we prefer to run — and have run on many of our proven builds.


Choosing the Right Injectors

When you're picking injectors, the general rule is: you can always go bigger. Let’s say your stock injectors are cooked, but you're not ready to upgrade the turbo yet. If you know you're eventually going to throw on something like an S467 and aim for 800 horsepower, then go straight to a set of 100% over S&S Diesel Motorsport injectors now.

With proper tuning — like we run at Full Send Diesel — the truck will run great in the meantime. Then when you’re ready to upgrade the turbo later, all you need is a retune and it’s game on.

You can always detune bigger injectors, but you can’t squeeze more fuel out of injectors that are already maxed out. So think ahead — if future upgrades are on your mind, size up. If not, match your injectors to your current HP goal and keep it simple.


Choosing the Right Injection Pump

Same mindset applies to your CP3. Whether you’re going with a 10mm, 12mm, or 14mm S&S Diesel Motorsport CP3, make sure your pump can support your injectors and goals.

High-speed CP3s are awesome — but they’re really built for max-effort race setups. They can be harder to tune and aren’t necessary for most street trucks. For 90% of builds, a standard S&S pump will get the job done reliably and still rip.

At Full Send Diesel, we’ve run it all, and S&S is what we trust in our builds. It’s proven. It’s consistent. And it works.


Why You Should Run a Calibrated Rail Relief, Not a Rail Plug

Both the 5.9L and 6.7L Cummins come from the factory with a calibrated rail relief valve. The issue is — over time, the spring inside that valve weakens. So your tune might be calling for 27,000 PSI at wide open throttle, but your stock relief could be blowing open early at 20,000 or less. That pressure loss kills performance, and in some cases can cost you hundreds of horsepower.

Some guys replace it with a solid rail plug, thinking it’ll solve the issue. Sure, it holds pressure — but it gives you zero protection. If your tune isn’t perfect and rail pressure spikes, that plug has nowhere to bleed it off. Now you’re risking cracked injector bodies, split lines, or fuel leaking into the motor.

The right move? A calibrated rail relief from S&S Diesel Motorsport. It holds pressure when you need it, but vents safely if things go sideways. We stock them here at Full Send Diesel for 5.9L, 6.7L Cummins, and even Duramax platforms.

Skip the plug. Skip the worn-out factory valve. Run the calibrated relief and protect your investment.


Fuel System Horsepower Reference

All horsepower values referenced in this blog are measured at the crank & dependent on supporting modifications. The following charts were provided directly by S&S Diesel Motorsport.


Why We Use S&S Diesel Motorsport

At Full Send Diesel, we don’t just sell S&S — we run their parts on every single one of our high-horsepower builds. Their injectors and CP3s offer unmatched performance, consistency, and their customer service is second to none.

We’re not here to claim they’re the best — there are plenty of great fuel injection options on the market. But as a whole, S&S is our go-to. In our experience, they’ve given us no reason to ever run or sell anything else!

That’s why we back them. That’s why we run them. And that’s why we’re proud to be one of S&S Diesel Motorsport’s largest direct authorized dealers.

If you’re ready to level up your 6.7L Cummins build with proven parts:

Need help deciding? Reach out — we’ll get you dialed.
Sales@FullSendDiesel.com

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