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Exhaust/Exhaust Manifolds

Posted by Eric Rego on

One of the common questions asked by people who are thinking of performing a Cummins conversion relates to exhaust manifold configurations. For a B series Cummins, there are five basic styles of manifolds. The first two are known as low mount turbocharger manifolds. One of these is the automotive style which was used on the Dodge Ram pickup. This manifold places the turbocharger off to the side of the engine and at roughly the same level as the valve covers. This type of manifold can be used for a conversion, but may require modifications to the right side panel and will require that the exhaust stack be placed off to the side of the hood. The other style of low mount turbocharger manifold places the turbo under the manifold and tucked in near to the block. This style of manifold can create interference issues when using an SAE 3 bell housing with a high mount starter. Both styles of low mount turbocharger manifolds tend to create complexity when performing a conversion.

 

The next two variations of manifolds place the turbocharger above the manifold and are known as high mount turbocharger manifolds. These manifolds are distinguished by the direction which the the turbocharger outlet faces. One manifold points the outlet of the turbine housing towards the rear of the engine (high mount turbo, rear exhaust) and the other points the turbine housing towards the front of the engine (high mount turbo, front exhaust). Either of these two manifold versions will keep the turbocharger and exhaust routing tucked inside the existing sheet metal.

 

An Example of a High Mount Front Exhaust Manifold

 

Lastly, there is a manifold which is used on naturally aspirated engines and routes the exhaust directly upwards out of the manifold.

 

The rest of this article will be devoted to the basic theories of designing an exhaust system. If the desire is to leave the original hood unaltered, often an exhaust system will need to be fabricated to go between the turbocharger and the original exhaust location. Although creating such a system would seem like a straight forward exercise, it is important to understand the physics behind a good design to avoid potential reliability issues. Much of what will be discussed is to help develop a thought process to avoid problems and to assist in understanding a failure if one were to occur.

 

One of the challenges with engine mounted components is dealing with vibration. High mount exhaust systems tend to be more susceptible to the effects of engine vibration because of the component's distance from the engine's center of gravity. A good way of thinking about engine vibration is that for every action, there is an equal and opposite reaction (which is Newton's third law of motion). Every time a cylinder fires, the resultant force essentially acts like a hammer delivering an impulse of energy to the engine's structure. This is the “action” or what is sometimes referred to as a forcing function. Once this energy is delivered to an engine's structure, the components which make up an engine react by moving. Because of this repeated hammering which occurs in an engine, the components end up moving in an oscillating fashion known as vibration. The way vibration is quantified is with frequency, or oscillations (cycles) per unit time.

 

All structures and components have what is known as a natural frequency. When the frequency of energy impulses equals that of the structure's natural frequency, the amplitude or distance that a structure moves can increase many fold. When this occurs, it is known as resonance. A good example of this principle is with an unbalanced tire. Often a tire's imbalance may only be detectable at a certain speed. The imbalance is always present regardless of speed, but at a certain speed, the frequency of the imbalance equals that of the suspension's natural frequency and the whole vehicle will shake. This concept is important because when a component enters into resonance, often failure is imminent due to the extreme forces which result.

 

Looking at the fundamental equation for natural frequency, it becomes apparent how to design a good engine mounted exhaust system.

 

 

In this equation, “k” represents a component's stiffness and “m” represents a component's mass. A higher natural frequency is better, therefore, based on the above equation, a higher natural frequency can be achieved with stiffer components or lower mass.

 

Simply using big heavy components for an exhaust system is not necessarily a good solution since it can be difficult to increase the stiffness of every aspect of the system to counteract the added mass. When a system is not designed as a “system,” a weak link can be created and a failure may result. The best solution is to keep the components of an exhaust system as light as possible, but well supported with stiff brackets and robust mounting points.

 

If the location of the turbocharger high above the engine's center of gravity isn't enough of an issue with high mount exhaust systems, the shear mass of the turbocharger creates its own set of problems. Because of it's large mass and cantilevered mounting, a turbo charger can have a high degree of displacement as it vibrates. This high displacement can be transmitted to the rest of the exhaust system and result in fatigue failures of components (cracked pipes and welds, broken mounts, etc.). There are two best practices for dealing with turbocharger vibration. One is to have the entire exhaust system secured to the exhaust manifold which allows for all the components to move together. If the exhaust system ends up being quite large and requires attachment points to other locations on the engine besides the manifold, it may be advised to have a soft coupler between turbocharger and the rest of the system by using a bellows or similar type of joint. Using a bellows is not always required as long as there is enough inherent flex built into the system, however, it can be difficult to determine if enough flex is present without some level of analysis or testing.

 

High Mount Front Exhaust (Turbo Foot Located Between Cylinders 1 & 2)
Case IH Models (Not an Exhaustive List) Manifold Specific Part Numbers
Tractors 5130 (Turbo Version), 5140, 5230 (Turbo Version), 5240, 5250 Description Case IH P/N Cummins P/N
Combines 1640 (After S/N JJC0034705), 1644, 2144, 2344 Manifold J931747, J901683 3901683, 3931747
Construction 621B, 621C, 621D, 850G, 850H, 850K, 1150H Turbo Drain Line J934093, J918579 3934093, 3918579
Turbo Oil Supply (21.25”) J918562 3918562
High Mount Rear Exhaust (Turbo Foot Located Between Cylinders 3 & 4)
Case IH Models (Not an Exhaustive List) Manifold Specific Part Numbers
Tractors 2096, MX100, MX110, MX120, MX135, MX150, MX170 Description Case IH P/N Cummins P/N
Windrower 8880, 8880HP Manifold J931745 3902347, 3931745
Construction 9030B Turbo Drain Line J944048, J905202, J918583 3944048, 3918583, 3905202
Turbo Oil Supply J920603 3920603
Naturally Aspirated Exhaust
Case IH Models Manifold Specific Part Numbers
Tractors 5130/5230 with 6-590 Engine Description Case IH P/N Cummins P/N
Manifold J901326 3901326

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