There are two different types of turbocharger manifolds; cast log style and welded tubular style
Manifold design on turbocharged applications is deceptively complex as there many factors to take into account and trade off
General design tips for best overall performance are to:
Cast
manifolds are commonly found on OEM applications, whereas welded
tubular manifolds are found almost exclusively on aftermarket and race
applications. Both manifold types have their advantages and
disadvantages. Cast manifolds are generally very durable and are
usually dedicated to one application. They require special tooling for
the casting and machining of specific features on the manifold. This
tooling can be expensive.
On the
other hand, welded tubular manifolds can be custom-made for a specific
application without special tooling requirements. The manufacturer
typically cuts pre-bent steel U-bends into the desired geometry and
then welds all of the components together. Welded tubular manifolds are
a very effective solution. One item of note is durability of this
design. Because of the welded joints, thinner wall sections, and
reduced stiffness, these types of manifolds are often susceptible to
cracking due to thermal expansion/contraction and vibration. Properly
constructed tubular manifolds can last a long time, however. In
addition, tubular manifolds can offer a substantial performance
advantage over a log-type manifold.
A design feature that can be common to both manifold types is a " DIVIDED MANIFOLD" , typically employed with " DIVIDED "
or "twin-scroll" turbine housings. Divided exhaust manifolds can be
incorporated into either a cast or welded tubular manifolds.
The concept is to DIVIDE or separate the cylinders whose cycles
interfere with one another to best utilize the engine's exhaust pulse
energy.
For example, on a
four-cylinder engine with firing order 1-3-4-2, cylinder #1 is ending
its expansion stroke and opening its exhaust valve while cylinder #2
still has its exhaust valve open (cylinder #2 is in its overlap
period). In an undivided exhaust manifold, this pressure pulse from
cylinder #1's exhaust blowdown event is much more likely to contaminate
cylinder #2 with high pressure exhaust gas. Not only does this hurt
cylinder #2's ability to breathe properly, but this pulse energy would
have been better utilized in the turbine.
The
proper grouping for this engine is to keep complementary cylinders
grouped together-- #1 and #4 are complementary; as are cylinders #2 and
#3. Because of the better utilization of the exhaust pulse energy, the
turbine's performance is improved and boost increases more quickly.
Manifold design on turbocharged applications is deceptively complex as there many factors to take into account and trade off
General design tips for best overall performance are to:
- Maximize the radius of the bends that make up the exhaust primaries to maintain pulse energy
- Make the exhaust primaries equal length to balance exhaust reversion across all cylinders
- Avoid rapid area changes to maintain pulse energy to the turbine
- At the collector, introduce flow from all runners at a narrow angle to minimize "turning" of the flow in the collector
- For better boost response, minimize the exhaust volume between the exhaust ports and the turbine inlet
- For best power, tuned primary lengths can be used
Cast
manifolds are commonly found on OEM applications, whereas welded
tubular manifolds are found almost exclusively on aftermarket and race
applications. Both manifold types have their advantages and
disadvantages. Cast manifolds are generally very durable and are
usually dedicated to one application. They require special tooling for
the casting and machining of specific features on the manifold. This
tooling can be expensive.
On the
other hand, welded tubular manifolds can be custom-made for a specific
application without special tooling requirements. The manufacturer
typically cuts pre-bent steel U-bends into the desired geometry and
then welds all of the components together. Welded tubular manifolds are
a very effective solution. One item of note is durability of this
design. Because of the welded joints, thinner wall sections, and
reduced stiffness, these types of manifolds are often susceptible to
cracking due to thermal expansion/contraction and vibration. Properly
constructed tubular manifolds can last a long time, however. In
addition, tubular manifolds can offer a substantial performance
advantage over a log-type manifold.
A design feature that can be common to both manifold types is a " DIVIDED MANIFOLD" , typically employed with " DIVIDED "
or "twin-scroll" turbine housings. Divided exhaust manifolds can be
incorporated into either a cast or welded tubular manifolds.
The concept is to DIVIDE or separate the cylinders whose cycles
interfere with one another to best utilize the engine's exhaust pulse
energy.
For example, on a
four-cylinder engine with firing order 1-3-4-2, cylinder #1 is ending
its expansion stroke and opening its exhaust valve while cylinder #2
still has its exhaust valve open (cylinder #2 is in its overlap
period). In an undivided exhaust manifold, this pressure pulse from
cylinder #1's exhaust blowdown event is much more likely to contaminate
cylinder #2 with high pressure exhaust gas. Not only does this hurt
cylinder #2's ability to breathe properly, but this pulse energy would
have been better utilized in the turbine.
The
proper grouping for this engine is to keep complementary cylinders
grouped together-- #1 and #4 are complementary; as are cylinders #2 and
#3. Because of the better utilization of the exhaust pulse energy, the
turbine's performance is improved and boost increases more quickly.