When it comes to GM pickups, there isn’t a better engine option than the 6.6L Duramax diesel. Introduced in ‘01, the Duramax was practically a Formula One engine in its time, with revolutionary aluminum heads and common-rail injection. There were a few shortcomings however, and it’s those issues that we’ll be addressing in our testbed 120,000-mile ‘04.5 Cheverolet 2500 HD.

New for the 2004 half-year was a VGT turbo, which flowed more than the previous LB7 turbo, and also had variable vanes, which allowed for the new LLY engine to spool up much quicker than the previous LB7. Just like many changes however, there were shortcomings to this new design. Thankfully though, they’re pretty easy to fix!

The Bad

When the LLY engine was designed, the intake was made to be free-flowing, but the post-turbocharger intake horn was not. In fact, it’s much, much smaller than the turbocharger inlet, which creates a bottleneck, especially at wide open throttle or when towing. Remember that the turbo will still try to force the air into the engine, creating higher boost pressures and hotter air (and therefore higher exhaust gas temperatures and engine operating temperatures.)

The Fix

Since our testbed Duramax-powered Chevy ran a little on the hot side anyways (especially in 90 to 100 degree weather) this opportunity seemed like the perfect time to test Pacific Performance Engineering (PPE’s) LLY turbo inlet upgrade kit. Unlike the factory piece, the PPE unit doesn’t neck down at all, creating a much more free flowing intake path with less restriction to the engine. The undersized factory turbo inlet creates a pressure drop in the intake air supply that feeds the turbo with super heated intake air.This air then enters the intercooler, which absorbs some of the heat and then passes this heat to the radiator that is positioned directly behind the intercooler. The cooling efficiency of the radiator is therefore reduced, leading to higher engine temperatures.


The intake mouthpiece was a fairly easy install, and it took our shop less than an hour to complete the job. With the LLY’s being great trucks (other than their cooling issues) we could now rest easy that the engine was running a few degrees cooler (with more power capability), and at least one of the truck’s cooling issues could be crossed off the list.

We started off with a stone-stock ‘04.5 LLY-powered Chevrolet, that had low miles but
was running hot. One of the first modifications we sought to do was an air intake horn that would allow a freer airflow path to the engine.
For our first step, we removed the plastic air intake hose by removing the tube connecting the airbox to the turbo intake horn. The airbox needn’t be removed for this install.
Next we removed the “6.6L” engine cover which would allow us access to the intake horn.
Some of the engine’s wiring looms were in the way, so those were carefully loosened from their mounts and moved aside by the truck’s owner.
Now we had full access to the factory intake horn, which was already looking restrictive to us.
After loosening the clamps from the intake horn into the turbocharger, we were able to remove the factory intake horn.
PPE’s intake kit comes with its upgraded intake horn, boot, and clamps to secure the new higher-flowing intake to the turbo and the airbox.
The air inlet on the factory intake horn was small, but it necked down even more inside the horn; much smaller than the turbo inlet. This is the restriction people talk about when referring to the stock intake.
The Pacific Performance Engineering intake horn is much larger at both the inlet, and through the entire piece, leading to a much larger area of airflow.
With both pieces off the truck, the smaller rubber boots were transferred over to the PPE intake horn.
It was a tight fit, but the PPE intake nestled right in the valley of the engine in front of the turbocharger.
With the intake horn installed and all the boots and hoses connected, it now was time to connect the intake horn to the rest of the system.
The factory intake tube makes a bend that the PPE piece no longer needs, so a chop saw was used to shorten the factory intake tube so it would fit.
After the intake was cut, it was filed along the edges to make sure no plastic got into the intake tract.
In the few final steps, the factory airbox tube was first connected to the airbox.
Next, the modified factory tubing was connected to the PPE intake horn giving an ultra-free airflow path.
The factory “6.6 Duramax” plastic engine cover was installed as a final step.
With PPE’s intake horn installed, we now had an unimpeded airflow path to the engine, leading to cooler inlet and engine temperatures!

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