Based on experimental results, I decided to improve both turbo response and the potential overheating issue with my truck’s Duramax engine.
It seems that the LLY engine ('04-'05) suffers from a constricted turbo elbow. This causes intake air to be compressed and heated (there’s science for ya!) as it changes direction toward the turbo intake blades. The extra heat is removed via the inter-cooler and rejected by the radiator, but that hot air stays under the hood and re-enters the system to form a weak positive-feedback loop when highly loaded.
A service bulletin from GM provides a solution, albeit not a very convenient one: Replace the LLY intake with the LBZ intake, but this also requires the replacement of everything upstream to the air filter box. Fortunately, there is an aftermarket alternative. S&B makes a direct-fit replacement for the OEM intake elbow which has 78.6% less restriction of airflow.
It was fairly simple to install, taking about only an hour to do from start to finish.
I also confirmed that the CCV system was dribbling oil down the back of the intake elbow. Grody.
A test drive confirms better throttle response, less cruise-control hunting, and a slightly lower steady-state temperature than before the upgrade.
