Written by Patrick Ellis This is the grand question facing us all! If you are just beginning to modify your diesel, we can offer you some tips before spending money. Where do you see your truck's performance going? Are you looking for a small amount of power to help with towing or are you looking to run low 12's in the 1/4 mile? Regardless of which path you choose, there are some basic principles guiding each stragety. Making power with a diesel involves improving airflow and fuel. Whether you want 40 more horsepower or 400, airflow and fuel is what it comes down to. Let's start by discussing some basic principles of making power with a diesel. Airflow Improving airflow is a crucial ingredient to making big power with a diesel. The first step to improving it is removing the restrictive factory air intake and replacing it with a high-flow cold air intake system. We sell a variety of air intakes to improve flow, sound and performance. Next, look towards the intercooler. The factory intercooler - especially if you have a 2008 or 2009 truck - leaves a lot to be desired. Its a noticeably thin intercooler (compared to a 2007.5 or 5.9 stock intercooler) and this was done on purpose. The factory wanted the truck to run hotter to aid in regeneration. Well, now that you are thinking about performance and not regeneration, that thin intercooler needs to go! Cobbs Diesel Performance can hook you up with a Banks, AFE or BD intercooler that will lower your EGT's, keep your intake air temps down and improve overall airflow between the turbo and intake. The factory boost tube from the intercooler to intake horn is 2.5" in diameter. Whereas the boost tube from the turbo to intercooler inlet is 3". Being performance enthusiasts, we can't let this restriction hamper our trucks! AFE and Shibby Engineering offer upgraded boost tubes with 3" diameters that improve air flow. Next, we have the factory intake horn. One look at it and anyone can see this intake horn was not designed for performance. For one, there is an EGR solenoid bolted on top - which disrupts the flow of air into the intake. This robs efficiency. Next, the outlet (or mouth) of the intake horn is relatively small. Upgrading this intake horn will improve the flow of air! Lastly, we have the turbo itself. The stock VGT turbo performs admirably up to a certain point. What we've seen is that the turbo performs well up to around 500 horsepower at the wheels. Beyond that, it is far outside its efficiency range. Upgrading the turbo will allow the truck to make CONSIDERABLY more power and torque. Each turbo has different characteristics and performance gains, so analyzing them in detail will help you meet your goals (i.e. you don't want a sled pulling turbo for a drag racing truck, and visa versa). Exiting the turbo are your exhaust gasses - and this leads us to the exhaus system. The stock system is restrictive by nature - there is a catalytic converter in the downpipe, a DPF filter, a Nox filter and a resonator near the rear of your truck. All of which (with the exception of the resonator) are restrictive. You can upgrade your exhaust to a 4" or 5" performance system and reduce backpressure and improve the flow of air. The process of improving airflow takes you from mild to wild. How far you take the rest of the options is up to your goals for the truck and budget. Fuel The stock fuel system performs well for a stock truck. But once you add a programmer, its seen very quickly the stock fuel system cannot keep up. A popular upgrade for the 6.7 Cummins is adding an aftermarket liftpump. Cobbs Diesel Performance sells a wide array of Air Dog lift pumps - ranging from 100 gph to 150 gph systems. I run an Air Dog 150 in my personal 6.7 Cummins. An aftermarket fuel system performs several functions. The first - and arguably most important - is that it filters water and air from diesel fuel. Ever heard of people getting a bad batch of diesel fuel and ruining their injectors and CP3? I've seen and read about several, and ask anyone how much the dealer charges to fix it - estimates range from $12,000 up to $20,000! And the factory doesn't warranty it, so the cost falls on either the fueling station or insurance company. Neither of which seems like a fun fight. An aftermarket fuel system filters the fuel prior to entering the CP3 and removes water and air before it can rob power or harm the motor. In my opinion, this is one of the most important upgrades every diesel owner should do - from a peace of mind standpoint. Second, these aftermarket fuel system use high-flow pumps and larger fuel lines to feed more fuel into the CP3. More fuel equals more power. If you are using a programmer or downloader - and use the higher settings - you may experience a surging at WOT. What is the surging? Its the fuel rail being drained because the stock fuel system cannot supply enough fuel. Not only is this annoying, but prolonged exposure to a drained fuel rail can cause internal engine damage. Again, not good. Aftermarket systems - like Air Dog - keeps the fuel flowing regardless of your power output, so you can rest assured, your truck is getting the fuel it needs. Injectors. Injectors play a large role in dumping more into your motor. There are a wide variety of injector nozzles available for your 6.7 Cummins - and they range from 40 horsepower to over 100 horsepower increases. Choosing the right injector depends on the goals for your truck. Running 130 horsepower injectors on a stock truck will cause excessive EGT's and can overburden the stock turbo. So the goal here isn't to throw the biggest set of injectors you can in the truck. Instead, the injector size needs to match your fueling upgrades and the airflow of your turbo. As a general rule, 40 hp nozzles will work on a stock truck. 80 hp will require an aftermarket fuel system. Anything over 80 hp needs an upgraded fuel system, CP3 and turbo. The CP3. The CP3 is the gatekeeper if your fueling needs. It takes the fuel from your liftpump and feeds the rail, which supplies the injectors. If the CP3 output doesn't match your other fueling upgrades, you will be losing out on power! Most companies offer stage 1, stage 2, and stage 3 CP3's. A few even offer dual CP3's for high horsepower applications. A general rule is stage 1 adds 30% more fuel, stage 2 60% and stage 3 80%. The specific numbers will vary by manufacturer. As has been mentioned in this article, the stage should match the other fueling upgrades of the truck to maximize flow and performance. Using a stage 3 CP3 on a stock trucks is overkill. And using a stage 1 on a twin turbo truck means you aren't maximizing your fueling needs. Tuning Programmers and downloaders bring together all the components of making power with a diesel. Because they tend to cost less than fueling and airflow upgrades, they seem to be the first modifications done on a diesel truck. Below are some important factors about tuning options. 1) Not all programmers are equal. Some are designed for mild horsepower gains while others will shred your transmission or clutch right off the bat. Programmers make power by adding fuel and increasing timing. Other take it a step further and adjust the duration the injectors stay open. Some programmers plug into the OBD port and must be loaded to the truck and removed. Examples include the Bullydog PowerPup and Triple Dog, Superchips Flashpaq, PPE, XRT and Smarty. Others, like the Bullydog PMT and Edge Juice, offer a monitor that display EGT's, trans temp, boost, etc. These options are important because some users dont' want to buy and install mechanical guages - so the display monitor and programmer in one package work well for them. Others want the max power and tuning options available with the XRT or Smarty. Another set of tuning options include the TS Performance MP-8 and DiabloSport Extreme PowerPuck. These devices increase rail pressure and are a popular stack with the Edge Juice with Attitude and Bullydog PMT. They are NOT recommended for the Smarty or XRT since those units already increase rail pressure. 2) Buy the programmer that not only meets your needs now but in the future. We have found many people that come to us have already had two or three programmers in the past. This tells us their past purchases did not grow with the other modifications to their trucks. So whats important is stopping for a second, writing down your immediate needs for the truck (power, mileage, etc) and comparing them to the future goals of your truck. Matching the programmer with your needs can save you hundreds of dollars and headaches trying to sell a used unit in the future. 3) Because we are talking about clean diesel trucks, tuning is also tied dealing with the check engine lights from removing these systems. Unfortunately, you cannot just delete the DPF, cat and Nox filter and have a good sounding, good flowing exhaust with no adverse affects. And this is where tuning comes into play. You will need a programmer to clear or turn off the codes. Products like the Edge Juice and Bullydog PMT do not turn off the codes, they simply clear them each time you start the truck. The XRT and Smarty turn off the codes so there is never a check engine light for a deleted DPF or EGR. Furthermore, these tuners will reset the regeneration counter so you will never have a regeneration again (the Edge and PMT do not do this, so a regeneration is still possible depending on your truck's latest flash). Conclusion Okay, so you've spent the last 10 minutes reading this article and things may be clear as mud - and that's good. We don't want to sell you products you don't want, we want you to think about your modifications, plan them carefully, and enjoy the truck! John and I are both diesel enthusiasts and own the trucks we sell parts for. We know what its like to outgrow a programmer, have our fuel rails drained with a stock fuel system, wrench underneath our trucks installing an exhaust system, etc. So we are trying to help you build the truck you want, while being aware of how each part is related to another. When I first started modding my truck, a guy told me, "For every part you buy, you'll need two or three more to support it." And that's true. So if you are still confused about what parts you need, how they fit together, or need help putting a plan together to build your truck, give John or myself a call. We love talking about diesel performance and have the products you need to build the truck of your dreams.