Part 9: Boosting the Airflow
Project Looks. Muscle. Longevity is back for another round of aftermarket bolt-ons for the ninth part of the major overhaul of our 2012 Silverado HD. This month things get serious, and we’re lifting the cab to install the first batch of major upgrades under the hood. The 2011-2016 LML runs well in stock form and made 496 hp in this truck with the Edge Evolution tuner, FASS lift pump and some basic bolt-ons. The factory turbocharger should support 520-530 hp, but, thanks to our fuel rail pressure dropping at wide-open throttle, getting that extra 40 hp wasn’t going to happen with the tired injection pump. Since we’d planned on doing some exhaust manifolds, bigger injection pump, modified VGT turbocharger and some high-flow charge air piping on the truck, it’s easier to do it all at once. We opted to raise the cab, allowing easier access and better photo documentation of the process. This can all be done with the cab on, it’s just really labor-intensive. For now we’ll focus on the airflow side of things and get to the injection pump stuff next issue.
When it came time to start the job, the loan of a two-post lift and some shop space at nearby Baker’s Diesel in Ogden, Utah, and a stuffed toolbox were all we needed. Baker’s technician Taylor Thompson had the A/C system evacuated, coolant drained, e-brake cable disconnected, steering shaft apart, and all the associated wiring harnesses and hoses apart, with the cab bolts out and the cab ready to go in the air, in under two hours. Once the cab was off, there was all sorts of room to work around the engine to start getting new manifolds, up-pipes, turbocharger, downpipe and injection pump swapped out for the upgraded aftermarket replacements.
ProFab Manifolds and Up-Pipes
The factory exhaust manifolds and up-pipes serve their purpose but leave a lot on the table when it comes to airflow and efficiency getting spent exhaust gasses to the turbocharger. The factory manifold takes exhaust through a decently sized entry port from all four cylinders but tries to cram it through a very restrictive runner. Exhaust entering the manifold from the back two cylinders must take a hard 90-degree turn, which disrupts airflow and creates unneeded turbulence. After exiting the manifold, the factory up-pipes use stamped, MIG-welded, tight radius bends and restrictive 1 5/16-inch bellows that are prone to cracking.
To fix these issues, Rick Lance at ProFab Performance developed complete replacement cast manifolds that work on any year Duramax and offer smoother transitions and longer runners for each cylinder. The design of the manifold improves the pathway for exhaust gasses to flow more freely, making the system work more efficiently. This helps in getting exhaust energy to the turbocharger for better spool-up and lower EGTs under load. To go along with the better-flowing manifold, the TowFlow up-pipes are built specific for the CastFlow manifolds and have longer sweeping bends and a larger, more durable 1 ¾-inch bellows—no more choke points for the pre-turbo exhaust.
ProMax 64 Variable Vane Turbo
Speaking of the turbo, the stock variable-vane unit on these trucks works well at sub-500-hp levels and had no issues towing the 9,600-pound fifth wheel through the spring. But any real horsepower fan would agree—why settle for 500 hp when it could be 600? We’re still in the early stages of owning this LML, but after daily driving an 800-hp LB7 Duramax it’s only a matter of time before this one starts pushing the envelope too. So, with hopes of making this a 600+ horsepower daily driver, the factory turbocharger had to go. Maintaining the drivability and quick, responsive turbocharger without losing the factory exhaust brake was key, so the VVT-style turbo had to stay. The options for modified stock turbos on the 2011-2016 Duramax have grown. High Tech Turbos’ ProMax 64 caught our eye since it had been on the market for quite some time and had proven 600+ results in multiple trucks.
The ProMax uses a 63.5mm forged milled compressor wheel from the S300 SX-E BorgWarner line that HT Turbo has modified to fit in the factory Garrett turbocharger. The wheel design offers a very broad map, which means power and torque is available wherever you need it. To reduce exhaust backpressure and improve turbine flow, a larger 10-blade turbine wheel replaces the factory 12-blade wheel. This combination paired with the factory variable vane exhaust housing means good low-end response with gobs of top-end power when compared to a stock turbocharger. The exhaust brake still functions when trying to slow a heavy load and that big exhaust wheel makes for a throaty exhaust note with plenty of whistle to let everyone know the truck means business.
HSP Diesel Maxx Flow Kit
Since the new turbocharger was going to be moving substantially more air through the system, replacing the factory intercooler piping and Y-bridge feeding the heads was a no-brainer. The factory pieces have multiple necked-down areas, tight sharp radii and restrictions that can be easily replaced with the Maxx Flow charge air piping kit from HSP Diesel. After having such great success with the traction bars previously installed on the truck from HSP, choosing them for more fabricated parts was an easy decision. The mandrel-bent, 3-inch cold and hot side piping make for an easier pathway for charge air to travel through the intercooler and into the engine. A CNC-machined Y-bridge also improves efficiency and better directs air into the cylinder heads, all of which helps with better throttle response, improved spool-up and lower charge air temperatures. We also installed the company’s mandrel-bent turbo mouth piece for the VGT turbo, which again flows much better than stock. Meaning the new 63.5mm FMW compressor wheel can get all the air it needs from the Edge Jammer cold-air intake. To top it all off, HSP Diesel offers in-house powdercoating with just about every color under the sun available. We opted for a deep metallic candy red with gloss black accents and clamps.
The design of the [profab performance] manifold improves the pathway for exhaust gasses to flow more freely…
While this isn’t everything we installed while the cab was off, we’ll wait until next issue to get into the reasons behind upgrading to an Exergy Performance CP4.2 injection pump. The new pump and turbocharger did require custom programming for best results, so GDP Tuning will be tasked with getting all these new parts working flawlessly together. We will tell you this: The 6.6L Duramax sure loves the extra air and we’re seeing lower EGTs sustaining max rail pressure under wide-open throttle, and we are creeping up on 600 rear wheel horsepower. It may be time to start looking into upgrading the factory Allison transmission and brakes. The quest for more out of Project Looks. Muscle. Longevity continues.
High Tech Turbo