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.

To improve turbocharger performance, CastFlow manifolds and TowFlow up-pipes from ProFab Performance were chosen.
To complement the new ProMax 64 turbocharger, high-flow charge air piping from HSP Diesel will really help keep air moving free through the system. The new mandrel-bent, 3-inch piping improves overall flow and reduces restrictions within the factory system. Hundreds of choices for powdercoat colors makes this a fun upgrade since everyone loves a little bling under the hood.
While it may look daunting and appear to be a ton of work, in all honesty these newer trucks are almost designed to be worked on this way. GM has made it pretty simple to remove the cab, and with the host of modifications being done to the engine, spending two hours pulling the cab off saved probably 10 hours of cussing, fighting and lying upside down on our heads trying to get to everything we needed to remove.
With the factory manifolds removed you get a good look at those factory aluminum cylinder heads. Remember back when GM announced the Duramax platform in 2001 and how much concern there was about how they’d make aluminum heads survive on a diesel? Turns out it wasn’t an issue at all and every version of the Duramax engine has just continued to get better.
The factory manifold looks ridiculous next to the new CastFlow from ProFab. It doesn’t take a degree in flow dynamics to understand how those longer sweeping runners can improve exhaust flow to the turbocharger. No more necked-down areas in the castings, no more tight 90-degree turns… just smooth, easy passages to keep exhaust flowing through the system.

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.

ProFab has taken advantage of every bit of space they can between the frame rails. To get as much out of the longer runner design as possible, the outlet of the manifold sits noticeably further out away from the cylinder head, meaning new up-pipes will be required to attach them to the turbocharger’s inlet volutes.
The TowFlow up-pipe kit fabricated specifically for the new manifolds fit perfectly and even bolted right up to the factory EGR Cooler. It’s a shame hiding these away so far in the engine bay, as the quality TIG welds and ceramic coating looks great and ensures thousands of trouble-free miles, along with great turbocharger performance with the better-flowing bellows.
The new ProMax 64 turbocharger from High Tech Turbo sure looks nice dressed up in fresh powder and ceramic coatings. With it sitting next to the stock turbocharger you can see the obvious differences in compressor wheel design. Not only does it change from a 11-blade compressor to a better-flowing 7-blade, it’s also upped from the stock 60mm to a 63.5mm version better suited for the 400 to 625-hp range.

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.

The factory turbine wheel was used for its ability to spool quickly and offer great drivability while creating enough backpressure to force some exhaust flow through the EGR cooler for emissions control. This is all fine and dandy at the factory 370-hp level, but once tuned and looking to push 500+ it becomes a choke point.
Sticking with a Garrett turbine wheel design, High Tech Turbos steps up to a better-flowing 10-blade turbine wheel that is slightly larger than stock without being so big it becomes lazy and hard to spool. The wheel profile combined with the LML’s vane design retains great off-idle and midrange response but eliminates the exhaust restriction when trying to run efficiently at 600-hp levels.
You can see how much better the CNC-machined Y-bridge is going to flow compared to stock. This could be the most crucial point for air distribution within the engine, so making sure the boost can get through easily is key to good engine performance and efficiency.

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.

The new Y-bridge dropped right in to place and fit perfectly on top of the factory intake runners. Using the OEM gaskets, the bridge snugged down and sealed perfectly to the heads. No need to worry about boost leaks with this design.
With the factory sensors installed in the new downpipe, it was time to drop the cab back down into place on the frame rails of the truck. Replacing all these parts, including the CP4 injection pump, took less than 8 hours start to finish thanks to a skilled mechanic and the right assortment of tools.
On the 2011+ LML trucks the factory downpipe uses a strange, virtually smashed design. Obviously it had to be made to fit some bungs for sensors and the urea nozzle, but with available space between the engine and firewall it’s hard to understand the reasoning. Pacific Performance Engineering offers this direct-replacement, 3-inch downpipe that fits perfectly in the stock location and is a must-have on any LML truck, upgraded turbo or not.
With the cab back down, cooling and AC systems refilled and all the wiring harnesses reconnected, buttoning up the charge air piping was about all that was left. The fabrication and attention to details from the HSP Diesel crew really shows in the fitment; there was nowhere we had to be concerned about it rubbing or creating an issue down the road.


High Tech Turbo

HSP Diesel

ProFab Performance

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