Extinguishing Excessive EGT On An LBZ Tow-Rig

Exhaust gas temperature is the single most vital parameter to monitor on any diesel. Whether your truck has been highly modified, treated to moderate power upgrades, or is completely stock, you always want to keep EGT as manageable as possible. When the owner of this ’07 Chevrolet Silverado 2500 HD—a truck equipped with an S300 turbo system, a built Allison 1000, and EFI Live tuning—saw 1,300 degrees F on the pyrometer while towing, he wanted to cool things off sooner rather than later. His urgency to shed EGT was amplified by the fact that the engine under the hood was an LBZ, the Duramax that’s (arguably) the most prone to cracking a piston due to added power and excessive heat.

The path to shedding EGT began with a thorough cleaning of the cooling stack, which yielded no change. Next, the S366 was pulled from the valley and fitted with a tighter exhaust housing, the driver side exhaust manifold was replaced with one off of an LML, and the truck was re-tuned by the Duramax gurus at CTT Tuning. Encouraged by the 100-degree drop in EGT he experienced with those changes, the owner replaced the factory intercooler with a drop-in Mishimoto unit. Now, towing the same equipment trailer and mini-excavator down the interstate, he sees 1,000 degrees vs. 1,300 on the pyrometer. In the following pages, we’ll go over all the parts and pieces he used to solve his EGT issue.

The newfound power that came with scrapping the factory Garrett 3788VA VVT in favor of an S300 was cool, but the numbers showing on the Auto Meter Factory Match pyrometer weren’t. Towing at 73 mph, on flat ground, and with the Allison locked in Tow-Haul, the owner saw 1,300 degrees F, sustained. Not only did this force the driver to spend an inordinate amount of time watching EGT, but with the LBZ’s track-record of cracking pistons he began to worry about bottom-end longevity, too.
After zero headway was made by separating out the cooling stack and pressure-washing the exchangers, the owner gave an exhaust housing with a tighter A/R a try. While the 1.0 A/R housing that showed up on the S366 SX-E would provide good high rpm flow for making horsepower, a slightly more restrictive .91 A/R housing would produce quicker spool up and improved transient response.
While tightening up the exhaust housing’s A/R isn’t conducive to producing more horsepower, it does make a turbo more efficient at lower engine speed, and a simple exhaust housing swap can be done relatively cheap. In this case, the cost of the .91 A/R housing was only $165, with the 1.0 housing likely being worth a fair amount on the used market (and could help the owner recoup some of that expense). With the S366 SX-E pulled as a complete assembly, the 1.0 housing was quickly removed and the .91 housing installed in its place.
Once in position and re-fastened to the HSP Diesel T4 turbo pedestal, the oil feed was reattached to the top of the center cartridge. Oil supply comes from the passenger side the LBZ’s block with the S300 turbo system in the mix.
The owner also upgraded the driver side exhaust manifold to a factory LML unit at the same time. From the factory, the driver side manifold on all ’01-’10 Duramax engines is dented (or kinked) for steering shaft clearance. The factory LML version isn’t, and is said to offer more exhaust flow (albeit minimal). For just $89 through Xtreme Diesel Performance, it was a hard upgrade to pass up.
In the midst of the turbo and manifold changes, the owner also switched EFI Live tuners, giving CTT Tuning a call. After data logging the truck’s towing performance using his FlashScan V2, the guys at CTT were confident they could help bring EGT down.
A major benefit to sharing data log info is that your tuner is essentially allowed to peer into your engine to see what’s wrong or exactly which area is in need of optimizing. Data logging also leads to quick turnaround times for tuning fixes and tweaks, and almost always reduces the amount of revisions you need to get things just right. In this case, the folks at CTT Tuning built a tow-specific tune based on the owner’s mods and using the data logs he supplied them.
Back on the test loop, and running the same 73-mph across flat ground with the Allison in Tow-Haul, the pyrometer showed a consistent 1,200 degrees F. The exhaust housing, exhaust manifold, and custom-tailored tow-tune had combined to cool things off 100 degrees.
Believing the factory intercooler to be out of its efficiency range, an aftermarket unit from Mishimoto was next on the list. Despite its size (and being double the weight of the factory air-to-air exchanger), its heavy-duty, all-aluminum bar-and-plate intercooler is a direct-fit, drop-in replacement for all ’06-’10 LBZ and LMM trucks. It’s available in Stealth Black powder coat or the Sleek Silver version you see here.
Opting for Mishimoto’s complete intercooler kit meant that a hot-side intercooler pipe and cold-side pipes came along for the ride, which with their larger diameter help to open up boosted air’s pathway into the heads. Three of the company’s DuraCore silicone boots and six T-bolt clamps are also included in the comprehensive intercooler system.
Thanks to its 3-inch diameter, Mishimoto’s hot-side pipe opens up airflow between the turbo’s compressor outlet and the inlet of the intercooler. Enlarging both the hot and cold-side intercooler pipes has long-been proven to cool intake temps, drop EGT, and even free up a few additional horsepower on Duramax mills.
No plastic or crimped-on end tanks here. Cast-aluminum, precision TIG-welded end tanks make Mishimoto’s intercooler capable of standing up to extreme boost pressure. End tank wall thickness checks in at 4mm.
If you’ve spent any time around higher boost street trucks, you know what this lip means. Mishimoto rolls a bead around the outer diameter of the intercooler’s hot-side inlet to keep the boot from backing off under high pressure. The hot-side inlet for Mishimoto’s intercooler measures 3-inches, while the outlet is 3.5-inches.
All piping supplied in Mishimoto’s intercooler kit is made from mandrel-bent aluminum with smooth, sweeping transitions. The cold-side pipes feature CNC-machined, quick-disconnect flanges and measure 3.5 inches in diameter (again, opening up flow beyond stock). As a bonus, all intercooler plumbing is polished to a mirror shine for an aesthetically pleasing finished look.
Mishimoto boots are some of the finest quality silicone intercooler pipe couplers you’ll find. Their DuraCore technology entails a durable 5-layer construction that resists oil, extreme pressure, fuel, and that also rejects heat. Unlike cheaper alternatives, they won’t break down over time.
A direct, drop-in replacement, the Mishimoto intercooler doesn’t require a whole lot of aftermarket hardware to install. That said, you do need the two lower A/C condenser brackets, the two aluminum spacers, and the M8x1.25 bolt and washer shown here—all of which are included with the intercooler.
At 2.76 inches, the Mishimoto unit’s core thickness is nearly twice that of the OEM intercooler. But don’t let the Mishimoto core’s thickness intimidate you, there is plenty of room to accommodate the bigger intercooler into the factory cooling stack. Just make sure you have a helping hand when it’s time to lower the Mishimoto cooler into place. It’s roughly twice the weight of the stocker.
Stainless steel, constant-tension T-bolt clamps ensure the DuraCore intercooler boots never budge. Their consistent holding power lies in their spring-loaded design, and Mishimoto claims it’s engineered them to compensate for thermal expansion.
Although the installation is more than a couple-hour process, the job was very straightforward. And as we soon found out, the time and cost invested in installing Mishimoto’s intercooler kit was well worth it.
No, this image has not been Photoshopped. The Mishimoto intercooler, combined with the high-flow hot and cold-side pipes, dropped EGT by 200 degrees. Now, cruising the same route under the same conditions, the pyrometer holds steady at 1,000 degrees on flat ground. In a towing scenario, this is huge. Aside from the reduced stress the engine and turbo see as a result of being exposed to less heat, the owner isn’t forced to immediately back out of the throttle if he encounters a grade—and now he might not even lose any speed at all.


When it comes to ’17 model year trucks like this one, it’s believed Ford began installing the larger, stronger connecting rods starting with Job 2 trucks. In our quest to fi nd out if we have the “better” rods, we ran the truck’s VIN and build date by our contact at Ford, and were told our engine was in fact a Job 2. To fi nd out for sure, we’ll be taking a peek inside the engine next time, as the compound turbo system requires the oil pan be pulled. That’s right, we said compounds. In the second installment, we’ll be adding the highest quality turbo kit in the industry and replacing the valley charger with the hottest selling VGT on the market. Make sure you’re here for Part 2!


YEAR: 2007






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