Wehrli Fabrications new 4” Resonator Pipe and 3.5” Intake Horn offer increased airflow to the turbocharger for better performance, enhanced turbocharger sound, and much better looks under the hood.

Emissions Friendly Bolt-On Upgrades for the 2020 Duramax
When GM released the all-new 2020 Silverado and Sierra HD 6.6L Duramax, there was a lot of talk within the market. Some thought the new looks were a step in the right direction, some not so much. With that massive front-end and the bold, in-your-face grille and headlight combo it’s either a love it or hate it appearance. Whether or not you like the new looks on the 2020 trucks, there is no denying the incredible performance from that Duramax, especially now that it’s backed with an impressive 10-speed automatic transmission. In its fourth year now, the sixth generation 6.6L Duramax, dubbed L5P, is by far the best one yet. State of the art high pressure fuel injection systems, the new variable geometry BorgWarner turbocharger, and super-efficient emissions systems with even more cooling capacity, the L5P packs a big punch, at least as far as stock trucks are concerned. With a claimed 445hp and 910lb-ft of torque, and that 10-speed transmission ready to keep it in the peak power band whenever you need it, these Duramax trucks can get just about any job done without breaking a sweat.

Factory tail pipe on the 2020 Duramax
The factory tail pipe on the 2020 Duramax, with its giant trombone look, is a bit of an eyesore on an otherwise super classy truck. Obviously, due to the diesel particulate emissions system running so hot the vented tip is a necessity. But there are some aftermarket options to keep functionality but add some much needed style.

Of course, as a diesel performance oriented publication, Diesel World Magazine isn’t about to leave anything stock for long and the aftermarket is already coming on strong with upgrades for the 6.6L 2020 models. Like any other diesel truck, the 2020 6.6 L L5P platform can find a little extra easily with some basic add-ons to the intake and exhaust systems. While some of you may be hesitant or scared to make any ‘performance’ upgrades on an emissions equipped vehicle, rest assured the aftermarket is fully aware of the current regulations and there are a few willing to jump through the EPA’s hoops to have their product fully approved with CARB compliant products and EO numbers.

304 stainless 4” Filter Back kit
MBRP has been offering their filter back stainless-steel exhaust system for the L5P Duramax for a few years now and the new 2020 models are no exception. The new 304 stainless 4” Filter Back kit has a classic look to it thanks to the more traditional 5” polished tip that can be installed.

On the intake side of the engine, Wehrli Fabrication has been putting in all the extra hours and effort required to get their complete line of L5P products emissions tested and documented as emissions compliant, a process that is currently taking place. With the emissions side of things taken care of, we had no worries making their suggested upgrades to this brand new Denali’s engine. First off, the WC Fab 4” Intake Resonator Pipe. This pipe replacing the factory muffled plastic duct and will eliminate the large plastic turbo resonator box. The powder coated resonator pipe reduced air restriction for more airflow to the turbocharger, while really dressing up the engine bay. Removing the stock system silencers within the intake tract enhance that beautiful turbo sound and will help that turbo breathe better under heavy load. The pipe installs in a matter of minutes with no tuning required.

removal of factory exhaust
Installation of the filter back kits is rather simple but will require removing the factory sensors from the tailpipe section, to be reinstalled in the new MBRP system. On the 2017+ GM truck, the factory exhaust will need to be cut just behind the filter, where the new kit will slip over and clamp into place.

The second piece to the puzzle is upgrading the restrictive turbo inlet pipe with Wehrli’s 3.5” High Flow horn. In an otherwise stock truck, this simple upgrade will net some improvement in both power and sound. While this pipe works great on a stock truck, with no tuning, Werhli’s in-house testing was showing as much as an additional 25hp to the rear tires with the addition to this intake horn on a tuned application. The gains come from the larger free flowing mouth piece that mounts to your factory turbocharger. The factory injection molded plastic piece necks down to just 2 3/8” while the WC Fab piece uses a patent pending flow ring design to eliminate turbocharger surge while increasing airflow to the compressor wheel.

The new system fit just as nice as the factory tail pipe did and lined up perfectly with the factory rubber hangers. The exhaust system sensor was threaded into place and the supplied clamp tightened down to hold it to the previously cut stock pipe.

Now moving over to the exhaust side of the 6.6L engine, MBRP’s Pro Series exhaust is the perfect upgrade to keep the factory emissions equipment under the truck while improving exhaust flow and offering a little better looks. Constructed of T304 stainless steel for years of durability and stylish looks, this system will outlast the factory exhaust while being easy to clean and keep looking nice even in winter climates.  On the L5P trucks, the DPF-Back system is simple to install, with the toughest part of the job being cutting the factory system just behind the DPF so the new tailpipe can be slid on and clamped into place. Everything fit like factory and lined up perfectly with the factory hangers and exhaust sensors.

MBRP knows it’s important to keep those exhaust exit temperatures as cool as possible, so like the factory it’s designed with notches cut into the outlet pipe to direct outside airflow into the exhaust stream. Between this, and their tip design, where the 4” pipe will run almost the whole length inside the 5” tips, you won’t have to worry about discoloration of the polished stainless tips from excessive heat.

The new exhaust system won’t change the overall sound from the truck much since the catalytic converter and diesel particulate filter are left under the truck, but the new polished 5” stainless tip exiting under the rear fender definitely looks better than the factory trumpet does. The owner of this Duramax is a welder by trade and an avid outdoorsmen when work lets him escape to the mountains. This 6.6L is used pretty regularly for heavy towing duties, from a large toy hauler travel trailer to a fully loaded welding supply trailer, so getting the most of this truck is important. The 3500HD was exactly what he needed in a daily driver, but rest assured with a little bit of love and a few aftermarket parts, it’ll soon be an even better version of itself.

MBRP dual layer polished 5” tip
The dual layer polished 5” tip really finishes off the look on such a beautiful truck. The exit point looks so much better coming out from under the fender like a traditional exhaust would as well.
Wehrli Fabrications 4” Resonator Pipe and 3.5” Intake Horn
Wehrli Fabrications new 4” Resonator Pipe and 3.5” Intake Horn offer increased airflow to the turbocharger for better performance, enhanced turbocharger sound, and much better looks under the hood.
WC Fab's intake pieces
The installation of  WC Fab’s intake pieces is pretty straight forward and won’t take more than about an hour to accomplish with basic hand tools. Plus, you can say goodbye to the ugly plastic muffled pieces found in the factory intake tract.
2020 L5p Duramax 4 inch intake resonator pipe
The factory resonator was removed by just loosening up some worm clamps and sitting next to the new WC Fab pipe shows the obvious differences. Not only is the new powder coated piece much prettier under the hood, eliminating that muffled resonator will enhance that wonderful turbo whistle.
BorgWarner turbocharger factory billet compressor wheel
Removing the factory intake horn will take some patience and some wobbly sockets, and possibly even unbolting the A/C compressor for a little extra room to work. Once removed you’ll get a nice good look at that BorgWarner turbocharger and the factory billet compressor wheel.
 Wehrli L5P intake horn
The new intake horn is a direct replacement to the stock unit and even has a port for the factory PCV hose to attach to. Wehrli really did their homework here and has even gone through the steps required by the EPA to have their complete L5P product line certified for CARB and emissions compliancy.
Wehrli Intake horn high flow 3.5” surge ring
The new intake horn uses a high flow 3.5” surge ring that eliminates turbo surge while eliminating restrictions. The factory piece necks down to just 2 3/8”, so the new horn can show as much as 25-horsepower to the tires.
Powder Coated L5P Intake Horn
Coated in Wehrli’s own WC Fab Red, the new powder-coated intake pieces really bring an otherwise boring engine bay to life. Better performance and better looks. Sounds like a win-win to us.

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