Building a 650hp 2003-2007 5.9L Cummins
Posted on 07 October 2015
Building a 650hp 5.9L Cummins can have some pitfalls. The biggest questions aren't if the motor can do it - it's one of the most solid engine platforms to build. Instead, the question is about the hard parts, and specifically, if you tow with the truck. This guideline will help you through the process and highlight the key decisions to make.
Air. A turbo choice is the first decision to make. The question to ask here is, "Will I tow with the truck and do I mind turbo lag?" Turbo lag and towing don't go hand-in-hand. Most truck owners will want lag no worse than the stock turbo. If your truck is used for work or towing, and you want 650hp, we suggest a compound kit. Compound kits use a small turbo for quick response at low RPM's and it feeds a much larger turbo for EGT control and pulling power. The kits will typically use a 58-62mm turbo feeding a 71-80mm secondary turbo. The 58-62mm turbo is your drivability. The 71-80mm is your overall power potential and response on the mid and top end. For 650hp, a 58/71 is plenty capable of supporting that power.
If you do not tow with the truck, and want to save some money by running an upgraded single turbo, the choices are endless. Any turbo in the range of 62-75mm will be enough to hit 650hp on a dyno. The main difference between them is the amount of lag. A 62mm will be slightly slower than stock from a stop, but start to reach its max potential at 650hp. On the other hand, a 75mm will have substantial lag vs. stock (5-6 seconds worth), but will have enough air flow for 800-900hp on the top end. If 650hp is your ultimate goal, a 62-64mm turbo will serve you well. If you may want more in the future, consider a turbo in the 66-75mm range for future fueling upgrades.
Second is fueling. Stock fueling isn't enough to make 650hp at the tires. Depending on how many miles are on your Cummins, you may be able to swap injector nozzles - or a complete injector set may be in order. A 100-120hp injector or nozzle provides enough fuel delivery to reach the 650hp mark. The next step is supporting these injectors with the rest of the fuel system. The truck will need a Fass or Air Dog lift pump - preferrably 150 GPH or more. The CP3 (injection pump) will also need upgrading. A modified CP3 from Industrial Injection or Fleece Performance will provide the fuel delivery the truck needs for 650hp. Twin CP3 kits will as well. We prefer the ATS Diesel Twin CP3 kit because of its clean install and reliable operation. Rounding out the fueling is tuning. For 2003-2005 5.9's, the Smarty S-06, UDC or SSR tuners are our recommendation. For 2006-2007 models, EFI-Live will bring the hard parts together for smooth, reliable power.
Next is increasing the reliability of the supporting components. ARP head studs are a required upgrade to prevent headgasket issues. Stiffer valve springs prevent valve float (Hamilton valve springs work great). If the truck has an intercooler with plastic end tanks, you will want to consider an aftermarket all-metal unit. Finally, the powertrain. Manual trucks will need an upgraded clutch - a street dual disc will get the power to the ground reliably. If the truck is an automatic, it will need a complete build including a billet flex plate, billet input shaft, upgraded clutches and valve body.
At the end of these steps, your 2003-2007 5.9L Cummins will be over 600hp at the tires - and potentially farther, depending on tuning. Street Diesel Power has helped dozens of 2003-2007 truck owners reach the 600+ hp number. Call, message or email us with questions about your build! We can help you avoid some pitfalls - and save money along the way.