Real-World EGT Solution For a Working-Class Duramax

• September 23, 2020
• Story By
  Mike McGlothlin

Modern diesel owners have generally been spoiled with their truck’s ability to handle additional horsepower with very little, if any, negative side effects. However, when big performance gains are easy to come by, modifying your truck can become addicting—and sooner or later some of the vehicle’s functionality is compromised. Case in point, we recently stumbled upon an ’07 classic body Chevrolet Silverado 2500 owner with a heat dilemma. Specifically, an exhaust gas temperature (EGT) dilemma. After upgrading the turbocharger, adding larger injector nozzles, installing a stroker CP3 injection pump and building the Allison transmission to handle the added power, he found that his exhaust temps sat steadily at 1,200 degrees F when towing.

With a higher-flowing turbo in the mix, along with ECM and TCM tuning that had been tailored to his specific fueling mods, he began to wonder if the factory intercooler had become inefficient for his new power level. After all, he’d more than doubled the LBZ Duramax diesel’s factory horsepower rating. Desiring a direct replacement, he reached out to Mishimoto, a company that builds an intercooler that more than doubles the OEM unit’s core thickness yet drops right into place. To further open up the intake tract, Mishimoto’s full-on intercooler kit got the nod, complete with replacement hot and cold-side piping. The result? EGT dropped to a very manageable 1,000 degrees while steady-state towing.

The Problem

This is what the pyrometer gauge looked like cruising at 75 mph on flat ground with a trailer and equipment in tow, and with the Allison in Tow/Haul mode. If you’re already holding 1,200 degrees F and then hit any sort of grade, exhaust gas temperature (EGT) only increases from there—and 1,300 to 1,400 is the warmest you want a Duramax to see for any lengthy amount of time. Living above 1,300 degrees for much longer than 20-30 seconds sustained is asking for trouble. Like piston-melting trouble. Needless to say, the owner didn’t have a lot of wiggle room here if he came upon a big hill.

The Solution

Though noticeably thicker (and heavier) than the factory intercooler, Mishimoto’s intercooler is a direct replacement and fits all 2006-2010 Duramax-powered Chevrolet and GMC trucks (both the LBZ and LMM engines). The all-aluminum intercooler features a bar and plate core and can be had in either Sleek Silver or Stealth Black.

Cast-Aluminum End Tanks

The Mishimoto intercooler’s end tanks are constructed of cast-aluminum, which makes them extremely durable under high boost. End tank wall thickness measures 4mm. As for its ability to better cool the intake charge (and ultimately EGT), the Mishimoto unit boasts a considerably larger core volume and more surface area than the stock air to air cooler.

Mounting Hardware

Making the installation process as straightforward as possible, Mishimoto supplies the two brackets pictured above. These are the lower A/C condenser brackets. Also included are two aluminum spacers and one M8 x 1.25 bolt and washer.

High Boost Insurance

For utmost protection against blowing an intercooler boot under elevated boost pressure, Mishimoto rolls a bead around the hot-side air inlet. This pre-intercooler area is subjected to some of the highest boost and heat levels the turbo system produces, second only to the kind of boost the compressor housing outlet sees at the turbo. The hot-side inlet’s diameter measures 3-inches.

Mirror Finish Piping

As part of a complete intercooler kit, Mishimoto supplies the pieces needed to open up airflow both entering and leaving its intercooler (hot-side and cold-side, respectively). The hot-pipe (top) is 3-inches in diameter and routes compressed air from the turbo to the intercooler. The two 3.5-inch pipes install on the cold-side and feature CNC-machined quick-disconnect flanges. All piping is made from mandrel-bent aluminum for smooth, sweeping transitions and is polished to a mirror shine.

Durable Intercooler Boots

Mishimoto’s DuraCore intercooler boots are some of the finest quality silicone couplers you’ll find in the aftermarket. Their 5-layer makeup is designed to resist heat, oil, pressure and even fuel, which means they won’t fail in extreme working environments or break down over time. To secure each DuraCore boot to its specific intercooler pipe, Mishimoto also supplies constant tension (spring-loaded), T-bolt clamps.

Thicker Bar-and-Plate Core

A look from this angle shows you the huge difference in core size between the factory intercooler and the Mishimoto replacement. The Mishimoto intercooler’s core width is 2.76 inches, nearly twice the thickness of the stock unit. Don’t worry, plenty of space exists in the cooling stack on the ’06-’10 GM HD trucks to accommodate this bad boy.

After the Install

Rolling down the highway after the install, things were much cooler on the pyrometer. With the same trailer and load in tow, once again cruising at 75 mph on flat ground and with the transmission locked in Tow/Haul mode, EGT held steady at 1,000-degrees F. A 200-degree drop in EGT is huge in the diesel world, and especially so if you spend a lot of your time hooked to a trailer. Now, not only does the owner have more peace of mind and wiggle room when encountering a grade, but his turbocharger and engine are seeing less heat.