Newer diesel trucks, like the Chevrolet Silverado HD and GMC Sierra HD with the LML Duramax engine, use highly refined and advanced powerplants. They also boast the latest state-of-the-art emissions equipment, including SCR (urea injection) which are illegal to remove to make power the more traditional ways. Even with power numbers approaching 400 horsepower and 800 ft-lb of torque, there are still a lot of us diesel enthusiasts looking for more power. But the road to making more power has changed a bit to keep your rig emissions legal.
Fortunately there are aftermarket manufacturers working within the rules and confines of the regulations to help make more power while satisfying emissions requirements. CARB OE exemptions are relatively new to the diesel performance side of things and are becoming the “smog legal” benchmark. So opting for aftermarket goodies with the CARB stamp of approval is a great first step toward keeping your rig legal.
Based on the need and number of trucks on the road, several manufacturers have stepped up to the challenge of making emissions-friendly parts. The drawback to CARB EO certification is that the process is lengthy and expensive. The three products shown here did not have CARB OE exemptions as of our deadline, but by the letter of the law are emissions legal since they do not remove or bypass the emission control components.
To make some more power on this 2012 Chevy Silverado 3500 HD, we turned to the experts at Thoroughbred Diesel in Winchester, Kentucky. To help the LML Duramax engine inhale better we chose a K&N 63-Series air intake kit. We also opted for a MagnaFlow 4-inch diameter stainless steel DPF-back exhaust system in their new black ceramic-coated finish to match the truck. And to address fuel and timing issues, the crew installed the new H&S Performance Mini Maxx Street Tuner to electronically enhance the engine’s tuning.
Before any of the parts were installed, Wade McGinnis and Adam Mattingly strapped the dually down to Thoroughbred’s Mustang chassis dyno to get baseline performance numbers. As we anticipated, the LML was no slouch from the factory. We measured peaks of 343.7 horsepower and 626.5 ft-lb of torque. But, we all know there’s more potential in the 6.6L Duramax engine just waiting to be unleashed and we were on a mission to see if we could make more power without messing with or removing the emissions equipment.
After the dyno runs, McGinnis and Mattingly went to work on the truck starting with the K&N intake system. The system features K&N’s new diesel-specific high-flow washable/reusable air filter with 50 percent more filter material. It includes all of the hoses, tubes and clamps needed to install it in the truck, along with a metal heat shield to make sure the open-element filter pulls in as much cool outside air as possible. The installation is very straightforward and following the provided installation instructions makes it almost foolproof; it can easily be done in your garage or driveway with basic hand tools.
McGinnis and Mattingly also installed the H&S A-pillar and Mini Maxx Street Tuner in the truck with ease. Swapping out the pillar is easy and gives the Mini Maxx a good mounting location where it’s easily visible to the driver. Installation is straightforward with few connections, including plugging in the OBD adaptor, running a wire under the hood for power, and then routing the HDMI cable up the A-pillar for the Street Tuner.
The final piece of the upgrade puzzle for the LML Chevy was the MagnaFlow DPF-back exhaust system. The system installed on this truck features the black ceramic coating over the 4-inch diameter mandrel-bent stainless steel tubing with a 5-inch diameter cooled exhaust tip. Keep in mind, though, that this is largely a cosmetic and sonic upgrade, since there’s not a restrictive muffler being replaced and the tubing diameter is the same.
It does however sound good and the exhaust tip is in arguably a better position with the tip protruding slightly beyond the edge of the bed rather than being tucked up under the bed and bumper in the stock location. You’ll need a reciprocating saw and a long blade to cut the factory exhaust; otherwise it’s a simple bolt-on installation.
When the upgrades were finished, McGinnis and Mattingly strapped the big black Chevy back down to the Mustang chassis dyno for some more pulls. Peak horsepower rose to 417.7 with 743.9 ft-lb of torque with the new parts installed and the Street level tune uploaded to the truck. This is a significant improvement of 74 horsepower and 117.4 ft-lb of torque at peak output. Looking at the dyno graphs, the new setup provides more power across the board with a very significant bump in performance across the upper rpm range from about 2,600 rpm on up.
The following photos highlight the installation of all the parts. If you plan to do the install yourself, you can accomplish the mods in less than a day.
In Part 2, we’ll review the installation step by step.
MagnaFlow Exhaust Products
Text and Photos by Chris Tobin