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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.

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3 comments

  • Mike west: April 06, 2018

    Hello I am slowly but surely building my truck but I use it for towing and every day driving as well. I tow a pretty large fifth wheel a few times a year. Here’s a list of the mods I have so far.
    Jasper built trans with billet triple disc torque converter is what I was told when I bought it.
    Air dog fuel system lift pump
    Full four inch exhaust turbo back with ten inch tip
    Afe stage two intake
    Banks big red intake horn
    Motor was just rebuilt about 40k miles ago
    Bullydog gt tuner
    Glow shift gauges
    It’s 2004 2500 5.9 24 valve
    I’ve got a lot of weight added on this truck a big ranch hand bumper large winches front and rear a rather large headache rack with spare tire roof rack
    I usually have a fifth wheel hitch in the back and it has a 90 gallon transfer tank as well. The truck is currently showing that it gets about 16.5 mpg daily driving. Seems like I get about 350 miles out of the regular tank. I’m running 22 inch wheels with 35 inch toyo mud tires brand new. I got about 5 grand to spend and would like to get the truck some more power. I am thinking compound turbo inter cooler head studs maybe. Seems like it’s got a pretty good lag too it even with the tuner turned up to performance mode. Never run it in extreme. My egts stay around 1400 if I’m towing uphill for short distance temp doesn’t go above 220 maybe 225 on a long pull but usually stays under 210. And just cruising is at 192. Turbo boost seems to max out at about 35 wot. I’m a newly graduated auto tech but pretty capable and I’d like advice on what to add to max this truck out and be reliable. Thanks for your time and help

  • Street Diesel Power: September 11, 2017

    Hi Robert!

    For hard parts, a billet flex plate, billet input shaft, billet output shaft, performance clutches, bands, valve body and billet triple disc converter will hold it. There are options available for rebuild kits or complete transmissions already built with a factory warranty. Please contact us if we can price a setup from ATS, BD, Revmax, Suncoast or Firepunk!

  • Robert Williamson: September 07, 2017

    I have an automatic transmission to mine and what should I do to Beef It Up To Handle that much more power

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