Volume 1 Issue 4 - Diesel Articles

Duramax LLY Mouthpiece Air Flow Model

In the first model, representative of the stock LLY mouthpiece, air is flowing around zero-radius miter corners. The conduit narrows and then enlarges again. There are several flaws at work in this model that conspire to increase pressure drop which, because of the fight (remember the garden hose), means less and, in this case, hotter air flowing to the turbo. First, in the top airflow model on the next page, note the immediate flow separation at the inside of the turn on the first corner (Label A). The main flow stream, subjected to huge centrifugal forces (would you believe 9000 Gs?) then runs toward the outside of the turn. If you look at the blue lines of flow, you will see that as the main flow stream progresses, the lines get closer together toward the outside wall (B). This is a pseudo-compression and a result of the conduit’s restrictive nature. In this regime, a large low pressure area – like a hurricane – is created on the inside of the turn (C), the lighter colors depict these forces. The low pressure is pulling on the main flow: equilibrium is struck only at great cost to flow.

The air that centrifugally flows to the outside of the turn travels further than the air on the inside of the turn. Because of this, the air on the outside ends up travelling faster relative to the air closer to the inside of the curve. Friction between those air currents results from their speed variation. As these adjacent air streams slide across each other, viscous layers of friction are formed with more energy lost as it is converted to heat. On a molecular level, it is no different – and no less real – than rubbing your hands together. The only way to reduce the friction would be to give the turn a larger radius sweep. Finally, the formation of stagnation pools in the outside corners (D), adds to momentum losses.

Improved Air Flow Model

In the second flow model, the throat size is increased...

In this article...

• LLY Mouthpiece Air Flow
• Fantastic Voyage
• Induction System Restrictions
• LLY Overheating Scenario
• Performance Tuning-Boost Controllers
• LLY Induction Overhaul Kit

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Bonnes said:

	... do you know where to buy the aftermarket mouth piece for a 2006-2007 duramax in the article wrote byWritten by Michael Patton Monday, 28 December 2009 12:54 thank you
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April 30, 2010
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archimedes said:

	analogy in exhaust restriction Michael Is there an analogous arguement for the pinched driver's side exhaust manifold on the LLY? George
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August 23, 2010
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Michael said:

... Thank you for the question, and it is a good one! The restriction that exists in the referenced article is significantly more harmful, because it occurs on the suction side of a pump. Anyone who does pump installations will tell you, that a restriction on the suction side can produce 2, even 3 times the performance hit than the same restriction on the pressurized side. Taking this to your question, the manifold restriction exists after all thermodynamic processes have taken place. It doesn't therefore interupt any intended efficiency. It is merely an exhaust restriction. In that light also, the most gas volume flow the restriction will see, is that equivalent to one cylinder, since only one cylinder can fire at a time. This is primarily why that restriction has very little impact on operation at stock power levels...i.e., it's not much of a restriction. Hope that helps. All Products are found at killerbeeperformance.com

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August 24, 2010
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