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For best performance use factory ACDelco (A1618C) air filter element
in your LLY and NOT a cheaper alternative!!!
WHY DOES YOUR LLY DURAMAX ACT SLUGGISH,
GET POOR FUEL MILEAGE, OVERHEAT,
AND FAN CLUTCH RUN CONSTANTLY?
THE LLY TURBO PROBLEM IS POOR AIRFLOW DESIGN!
If you have been discouraged (pissed-off might fit better) with your 2004.5-2005 LLY lack of performance… the exciting news is… the problem has been identified and can be easily fixed!
The #1 Duramax model we hear performance complaints about daily is the 04.5-05 LLY. (The 2006 LLY DOES NOT have this issue because it has a much larger turbo inlet mouthpiece)
COMPLAINTS INCLUDE:
- Fan clutch constantly running
- Overheats pulling loads up grades
- Sluggish turbo response / throttle response slow
- Turbo failures
- Poor fuel economy
LLY owners tell us daily how they have made expensive aftermarket modifications to their truck (chips, air intakes, exhaust) … with little results.
The problem started in 2004 when GM when launched the LLY emmisions package to meet the mandated Clean Air Act and CARB standard for emissions improvement.
GM advertised its introduction of an emissions friendly engine which included a new variable vain turbocharger. Also new was an EGR inlet to re-circulate a small amount of exhaust gas back into the combustion chamber to reduce NOx emissions.
The LLY model Duramax replaced the LB7 with promises of more power and efficiency. From the start it became clear right away, there was a problem. The LLY did not live up to the promises. Economy was reduced, performance hindered, and many towing customers could not use it for the advertised load capability because of engine overheating issues. Compared to the 1st generation LB7 Duramax, it seemed to be dragging a small “anchor” behind it.
PROBLEM DISCOVERED
The main source of the LLY defect is the turbocharger inlet mouthpiece. The mouthpiece had been redesigned by GM to squeeze into a smaller space. This size reduction compromised the mouthpiece aerodynamically with a significant air restriction caused by SHARP RIDGE in the elbow which results in a "narrow throat” and poor airflow.
The Turbo Mouthpiece attaches to the inlet side of the turbo

NOTICE the sharp ridge in the throat?
The sharp ridge creates air flow resistance and turbulence!
This is a manufacture's design flaw!
The turbo inlet mouthpiece is made of a dense high-temp injection molded plastic. The design flaw was created by the injection mold leaving a sharp ridge at the elbow in the throat of the mouthpiece.
GM noticed this design flaw (but failed to mention it to LLY owners) and re-engineered the turbocharger mouthpiece to be larger and much less restrictive in the newer LBZ and LMM model years. In these newer models an increase in power and lower engine temps are all noticeably affected.
The enormous amount of airflow restriction caused by the sharp lip and the narrow “throat size” of the LLY mouthpiece forces the turbocharger compressor to work extra hard to deliver the air pressure and volume demanded by the ECM. Higher vane loads and lower max boost is the result.
Consider garden hose water flow. If you have an 80 psi water supply to the house, and you turn on the hose bib with no hose attached, you will get a huge 80 psi gusher. Now attach a 100 ft long, ½” diameter garden house, and that flow is reduced to about 30 psi at the outlet. This is because friction is eating away at the hose outlet pressure.
The same applies to the air induction plumbing to the turbocharger. A restricted air flow means the turbocharger needs to make more Boost to compensate for these losses. This means the compressor must work harder to create additional boost, spinning considerably faster to do it… that is a bad thing, not a good thing.
Eliminating air induction restrictions permit the turbo to work less to produce desired boost making it more efficient. The turbocharger becomes easier to drive which also increases longevity and reduces the amount of heat produced by the compressor. This means lower exhaust back pressure and lower EGT,
It does not matter what the air intake aftermarket manufacturers tell you their products do to reduce air restriction… they still don’t fix the LLY design flaw.
The constriction in the “throat” of the turbocharger inlet mouth piece must be eliminated for their products to work properly.
The solution is simple and inexpensive… so don't live with the problem!
REPLACE THE TURBO INLET MOUTHPIECE with an aftermarket 70% LARGER THROAT AFTERMARKET Mouthpiece that is a direct stock replacement.
"AFE" AFTERMARKET MOUTHPIECE:

WITH A 70% "LARGER THROAT" AFTERMARKET MOUTHPIECE BY AFE YOU WILL:
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Increased Air Flow "Volume" Which Means Better Turbo Efficiency
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Reduced Fan Clutch Operation And Hi-Load Overheating
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Higher Boost Numbers
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Quicker Turbo Spool And Throttle Response
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200-400 Degree Reduction In Peak EGT
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Installs In 30 Minutes With Clean OEM Appearance
INSTALLATION IS SIMPLE:
The turbo inlet mouthpiece is connected directly to the front of the turbocharger inlet with a "band clamp". Remove the black plastic resonator (black piece that says 6.6 Turbo Diesel) and the PCV hose... then loosen the band clamp and replace the mouthpiece.
PLEASE NOTE: Just changing out the flawed Turbo Mouthpiece will allow your turbocharger to operate and build boost much smoother... BUT if you are looking for up to 20% fuel mileage gains you also need to add the DURAMILEAGE™ tuning.
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