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Turbos 101-103

Old 05-27-2010, 05:41 PM
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Turbos 101-103

Thanks to Porthos for finding this information, this is slight revised to make sure we stay in compliance with copyright laws.

(Due to a clerical error the original was inadvertently deleted instead of stuck, those buttons are too close together.)

Turbos 101

Full Article in PDF.

How a Turbo System Works Engine power is proportional to the amount of air and fuel that can get into the cylinders. All things being equal, larger engines flow more air and as such will produce more power. If we want our small engine to perform like a big engine, or simply make our bigger engine produce more power, our ultimate objective is to draw more air into the cylinder. By installing a Garrett turbocharger, the power and performance of an engine can be dramatically increased.

So how does a turbocharger get more air into the engine? Let us first look at the schematic below:

1 Compressor Inlet
2 Compressor Discharge
3 Charge air cooler (CAC)
4 Intake Valve
5 Exhaust Valve
6 Turbine Inlet
7 Turbine Discharge The components that make up a typical turbocharger system are:
  • The air filter (not shown) through which ambient air passes before entering the compressor (1)
  • The air is then compressed which raises the air’s density (mass / unit volume) (2)
  • Many turbocharged engines have a charge air cooler (aka intercooler) (3) that cools the compressed air to further increase its density and to increase resistance to detonation
  • After passing through the intake manifold (4), the air enters the engine’s cylinders, which contain a fixed volume. Since the air is at elevated density, each cylinder can draw in an increased mass flow rate of air. Higher air mass flow rate allows a higher fuel flow rate (with similar air/fuel ratio). Combusting more fuel results in more power being produced for a given size or displacement
  • After the fuel is burned in the cylinder it is exhausted during the cylinder’s exhaust stroke in to the exhaust manifold (5)
  • The high temperature gas then continues on to the turbine (6). The turbine creates backpressure on the engine which means engine exhaust pressure is higher than atmospheric pressure
  • A pressure and temperature drop occurs (expansion) across the turbine (7), which harnesses the exhaust gas’ energy to provide the power necessary to drive the compressor

What are the components of a turbocharger?

Other Components
Blow-Off (Bypass) Valves
Oil & Water Plumbing
Which Turbocharger is Right for Me or more affectionately known as My Turbo & Me
Journal Bearings vs. Ball Bearings

Turbos 102

Full article in PDF.

Please thoroughly review and have a good understanding of Turbo Systems 101- Basic prior to reading this section. The following areas will be covered in the Turbo System 102 - Advanced section:
1. Wheel trim topic coverage

2. Understanding turbine housing A/R and housing sizing

3. Different types of manifolds (advantages/disadvantages log style vs. equal length)

4. Compression ratio with boost

5. Air/Fuel Ratio tuning: Rich v. Lean, why lean makes more power but is more dangerous
1. Wheel trim topic coverage
Trim is a common term used when talking about or describing turbochargers. For example, you may hear someone say "I have a GT2871R ' 56 Trim ' turbocharger. What is 'Trim?' Trim is a term to express the relationship between the inducer* and exducer* of both turbine and compressor wheels. More accurately, it is an area ratio.
* The inducer diameter is defined as the diameter where the air enters the wheel, whereas the exducer diameter is defined as the diameter where the air exits the wheel.
Based on aerodynamics and air entry paths, the inducer for a compressor wheel is the smaller diameter. For turbine wheels, the inducer it is the larger diameter (see Figure 1.)

Figure 1. Illustration of the inducer and exducer diameter of compressor and turbine wheels

Example #1: GT2871R turbocharger (Garrett part number 743347-2) has a compressor wheel with the below dimensions. What is the trim of the compressor wheel?

2. Understanding housing sizing: A/R
3. Different types of manifolds (advantages/disadvantages log style vs. equal length)
4. Compression ratio with boost
5. Air/Fuel Ratio tuning: Rich v. Lean, why lean makes more power but is more dangerous

Turbos 103

Full Article in PDF.
This article is a bit more involved and will describe parts of the compressor map, how to estimate pressure ratio and mass flow rate for your engine, and how to plot the points on the maps to help choose the right turbocharger. Have your calculator handy!!
1 Parts of the Compressor Map:
The compressor map is a graph that describes a particular compressor’s performance characteristics, including efficiency, mass flow range, boost pressure capability, and turbo speed. Shown below is a figure that identifies aspects of a typical compressor map:
◊ Pressure Ratio
◊ Mass Flow Rate
◊ Surge Line
The Choke Line
Turbo Speed Lines
Efficiency Islands
2. Plotting Your Data on the Compressor Map
Estimating Required Air Mass Flow and Boost Pressures to reach a Horsepower target.
Old 05-27-2010, 06:03 PM
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This Turbo Tech Section is intended to cover many of the auxiliary systems in a more complete
and in-depth manner than what is originally covered in Turbo Tech 101, Turbo Tech 102,
Turbo Tech 103 and Diesel Tech. With this additional section, you will better understand
how to optimize your turbocharger system.
Turbo System Optimization will cover:
  2. Application Information
  3. Turbo Match
  4. System Components
  5. Common Causes of Oil Leakage
  6. System Testing/Monitoring
  7. 11-Point Checklist

The website contains a lot of helpful information. It contains product information
about turbos, intercoolers, and turbo kits. It explains Garrett’s model nomenclature, it goes over Garrett’s technology
and product development as well as our involvement with OEM’s and Motorsports. It contains
tech tutorials written by the engineers from Basic, to Advanced, up to the Expert level where detailed formulas
are used to plot operating points on compressor maps to help select the correct turbo. It also contains
News and Events such as the GT ride of the month, the Garrett sponsored vehicles and what events we’ll be at
throughout the year as well as a distributor locator. The website has extensive information, both general and technical.
No matter what your experience level, you’ll find information that will help you with your specific
application or simply increase your knowledge of turbos and turbos systems.

2. Application Information

The most important thing to understand before designing a system is the application. Is it going to be used for road racing, drag racing or drifting or maybe it will be primarily a street driven car. The intended use greatly affects the turbo selection as well as the system components. A turbo system that works well for a 9 second drag car is most likely not going to work well for a drift car or road race car.

You need to have a target flywheel horsepower in mind.

The horsepower value will be used to help design the entire system. Every time the horsepower value is used to help define a system component, I’m going to place a turbo indicator there. At the end of the section we’ll see how many times we’ve used this horsepower value.

3. Turbo Match
  • Go to
  • Click on Turbo Tech
  • Read Turbo Techs 101, 102 and 103.
  • Using formulas in Turbo Tech 103, calculate mass flow and pressure ratio (PR) at redline for your specific application.
  • Plot mass flow and PR on several compressor maps to determine the best fit
  • For the example in this presentation, the "application" will be a 400 flywheel hp street car using pump gas, therefore the estimated mass flow ~ 40 lbs/min

4. System Components

Air Filter It is important to appropriately size the air filter for the maximum flow rate of the application.
For our specific example, we are looking for target face velocity of <=130 ft/min at redline to
minimize restriction so as to provide the turbo with all the air necessary for it to function optimally.
If the turbo does not have access to the proper amount of air, excessive restriction can occur and cause:
  • Oil leakage from the compressor side piston ring, which results in oil loss, a fouled CAC
    and potentially smoke out of the tailpipe.
  • Increased pressure ratio, which can lead to turbo overspeed.
  • Overspeed will reduce turbo durability and could result in an early turbo failure.
Determining the correct air filter size
Face Velocity = 130 ft/min
Mass Flow = 40 lbs/min
Air density = 0.076 lbs/ft3

Mass Flow (lbs/min) = Volumetric Flow Rate (CFM) x Air Density (lbs/ft3)

Volumetric Flow Rate (CFM) = Mass Flow (lbs/min) / Air Density (lbs/ft3)

Volumetric Flow Rate = 526 CFM

**For twin turbo setups, simply divide the flow rate by two.

Face Velocity (ft/min) = Volumetric Flow rate (CFM) / Area (ft2)

Area (ft2) = Volumetric Flow rate (CFM) / Face Velocity (ft/min)

Area (ft2) = 526 / 130 = 4.05

Area (in2) = 4.05 x 144

Area = 582 in2
Now that we know the required surface area that our air filter must have, we need to determine
the correct air filter size using information provided by the filter manufacturer. We will
need to know the following information about the filters we are considering:
  • Pleat height
  • Pleat depth
  • Number of pleats

Pleat Height = 9.00

Pleat Depth = 0.55 in.

# of Pleats = 60

Area (in2) = pleat height x pleat depth x # of pleats x 2

Area (in2) = 9.00 x 0.55 x 60 x 2

Area = 594 in2

Actual Filter Area (594 in2) > Calculated Area (582 in2)

Since the actual filter area (594 in2) is greater than the required area, this air filter will work for our application.
Oil Supply & Drainage
Journal Bearing Turbo
Journal-bearings function similarly to rod or crank bearings in an engine - oil pressure is required to keep components separated. An oil restrictor is generally not needed except for oil-pressure-induced leakage. The recommended oil feed for journal bearing turbochargers is -4AN or hose/tubing with an ID of approximately 0.25.
Be sure to use an oil filter that meets or exceeds the OEM specifications.

Ball Bearing Turbo
An oil restrictor is recommended for optimal performance with ball bearing turbochargers. Oil pressure of 40 - 45 psi at maximum engine speed is recommended to prevent damage to the turbocharger’s internals. In order to achieve this pressure, a restrictor with a 0.040' orifice will normally suffice, but you should always verify the oil pressure entering the turbo after the restrictor in insure that the components are functioning properly.
Recommended oil feed is -3AN or -4AN line or hose/tubing with a similar ID. As always, use an oil filter that meets or exceeds the OEM specifications.


Oil Drain In general, the larger the oil drain, the better. However, a -10AN is typically sufficient
for proper oil drainage, but try not to have an inner diameter smaller than the drain hole
in the housing as this will likely cause the oil to back up in the center housing. Speaking
of oil backing up in the center housing, a gravity feed needs to be just that! The oil
outlet should follow the direction of gravity +/-35° when installed in the vehicle on level
ground. If a gravity feed is not possible, a scavenge pump should be used to insure that
oil flows freely away from the center housing.
  • Undulations in the line or extended lengths parallel to the ground
  • Draining into oil pan below oil level
  • Dead heading into a component behind the oil pan
  • Area behind the oil pan (windage tray window) where oil sling occurs from crankshaft
When installing your turbocharger, insure that the turbocharger axis of rotation is parallel
to the level ground within +/- 15°. This means that the oil inlet/outlet should be within
15° of being perpendicular to level ground.
Old 05-27-2010, 06:08 PM
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Water Lines Water cooling is a key design feature for improved durability and we recommend that if your turbo has an allowance for watercooling, hook up the water lines. Water cooling eliminates the destructive occurrence of oil coking by utilizing the Thermal Siphon Effect to reduce the Peak Heat Soak Back Temperature on the turbine side piston after shut-down. In order to get the greatest benefit from your watercooling system, avoid undulations in the water lines to maximize the Thermal Siphon Effect.

Negative degrees: water outlet of center housing is lower than water inlet
Positive degrees: water outlet of center housing is higher than water inlet

For best results, set the orientation of the center housing to 20°.

Significant damage to the turbo can occur from improper water line setups.

Charge Tubing
The duct diameter should be sized with the capability to flow approximately 200 - 300
ft/sec. Selecting a flow diameter less than the calculated value results in the flow
pressure dropping due to the restricted flow area. If the diameter is instead increased
above the calculated value, the cooling flow expands to fill the larger diameter, which
slows the transient response.
For bends in the tubing, a good design standard is to size the bend radius such that it is
1.5 times greater than the tubing diameter.
The flow area must be free of restrictive elements such as sharp transitions in size or

For our example:
  • Tubing Diameter: velocity of 200 - 300 ft/sec is desirable. Too small a diameter will increase pressure drop, too large can slow transient response.
  • Velocity (ft/min) = Volumetric Flow rate (CFM) / Area (ft2)

Again, for twin turbo setups, divide the flow rate by (2).

Charge tubing design affects the overall performance, so there are a few points to keep in
mind to get the best performance from your system.
  • Duct bend radius:
    - Radius/diameter > 1.5
  • Flow area:
    - Avoid area changes, sharp transitions, shape changes
  • Available packaging space in the vehicle usually dictates certain designs
Selecting a Charge Air Cooler (aka intercooler) has been made simple with's intercooler core page. Each core is rated for horsepower,
making it as easy as matching your desired power target to the core.
In general, use the largest core that will fit within the packaging constraints of the application.

For our example:

Another important factor in selecting the correct intercooler is the end tank design. Proper
manifold shape is critical in both minimizing charge air pressure drop and providing
uniform flow distribution. Good manifold shapes minimize losses and provide fairly even
flow distribution. The over-the-top design can starve the top tubes however. The side
entry is ideal for both pressure drop and flow distribution, but it is usually not possible
due to vehicle space limitations.

Proper mounting of the intercooler increases the durability of the system. Air to air
charge air coolers are typically "soft-mounted", meaning they use rubber isolation
grommets. This type of mounting is also used for the entire cooling module. The design
guards against vibration failure by providing dampening of vibration loads. It also
reduces thermal loads by providing for thermal expansion.

Benefits of Isolation:
  • Guards against vibration by damping loads
  • Reduces thermal loading by providing for thermal expansion
Blow Off Valves (BOV)
Using the proper blow off valve (BOV) affects the system performance. There are
two main types to consider.
  • MAP (Manifold Absolute Pressure) sensor uses either a vent-to
    atmosphere valve or a recirculation valve.
    • Connect signal line to manifold source
    • Surge can occur if spring rate is too stiff

  • MAF (Mass Air Flow) sensor uses a recirculation (bypass) valve for best drivability.
    • Connect signal line to manifold source
    • Position valve close to the turbo outlet for best performance (if valve can handle high temp).
    • Surge can occur if valve and/or outlet plumbing are restrictive.

Internal wastegates are part of the turbo and integrated into the turbine housing. Two connection possibilities exist for signal line. The first is to connect line from compressor outlet (not manifold - vacuum) to the actuator. The second is to connect a line from compressor outlet to boost controller (PWM valve) and then to the actuator. Manifold pressure is limited by the spring rate of the actuator. Most OEM style actuators are not designed for vacuum, and thus, the diaphragm can be damaged resulting in excessive manifold pressure and engine damage.

External wastegates are separate from the turbo and integrated into the exhaust manifold rather than the turbine housing. Connection to the manifold greatly affects flow capability, and correct orientation of the wastegate to the manifold is essential. For example, placing the wastegate at 90° to the manifold will reduce flow capacity by up to 50%! This greatly reduces the control that you have over the system and puts your entire drivetrain at risk. Instead, the ideal connection is at 45° with a smooth transition.

There are two connection possibilities for signal line:
  • Connect a line from the compressor outlet (not manifold - vacuum) to the actuator
  • Connect a line from the compressor outlet to a boost controller (PWM valve)
    and then to the actuator
Again, manifold pressure is limited by spring rate of actuator.
Old 05-27-2010, 06:09 PM
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5. Common Causes of Oil Leakage

A properly installed turbo should NOT leak oil.

There are, however, instances where oil leaks occur. The most common causes,
depending on the location of the leak, are:
Leakage from compressor and turbine seals
  • Excessively high oil pressure
  • Inadequate drain, drain is too small, does not go continuously downhill,
    or the location of the drain inside the oil pan is located in a section that has
    oil slung from the crank causing oil to back up in drain tube. Always
    place oil drain into oil pan in a location that oil from crank is blocked by windage tray.
  • Improper venting of crankcase pressure.
  • Excessive crankcase pressure.
  • Oil drain rotated past the recommended 35°.
Leakage from compressor seal
Excessive pressure across the compressor housing inlet caused by:
  • Air filter is too small.
  • Charge air tubing too small or has too many bends between the air filter
    and compressor housing.
  • Clogged air filter.
Leakage from Turbine seal
  • Collapsed turbine piston ring from excessive EGT’s.
  • Turbo tilted back on its axis past recommended 15°.
6. System Testing and Monitoring

Many problems with turbo systems can be solved before the catastrophic happens
through simple system testing.
Pressurize system to test for leaks
  • Clamps
    - Check tightness
  • Couplers
    - Check for holes or tears
  • CAC core / end tanks
    - Check for voids in welds
The turbo system in your car should be monitored to insure that every aspect is
functioning properly to give you trouble-free performance.
Instrumentation used to monitor / optimize system
  1. Oil Pressure (Required to monitor engine operation)
  2. Oil Temperature (Required to monitor engine operation)
  3. Water Temperature (Required to monitor engine operation)
  4. A/F Ratio (such as a wideband sensor; required to monitor engine operation)
  5. Manifold Pressure
  6. Turbine Inlet Pressure
  7. Exhaust Gas Temperature
  8. Turbo Speed Sensor
  • The most accurate way to calibrate and optimize a system is through datalogging!
Manifold Pressure
  • Calibrate actuator setting to achieve manifold pressure required to meet hp target
  • Detect over-boost condition
  • Detect damaged actuator diaphragm
Back Pressure
  • Monitor pressure changes in turbine housing inlet
  • Affect of different turbine housing A/R’s
  • Increased back pressure decreases Volumetric Efficiency thus decreasing ultimate power
  • Monitor exhaust gas temperature (EGT) in manifold / turbine housing
  • Adjust calibration based on temperature rating of turbine housing
    material or other exhaust components
Turbo Speed
  • Determine operating points on compressor map
  • Determine if the current turbo is correct for the application and target hp
  • Avoid turbo over-speed condition, which could damage turbo
7. 11 Point Checklist
  1. Application Information - target horsepower, intended use of vehicle, etc.
  2. Air filter sizing - determine size for application needs
  3. Oil Supply - restrictor for ball-bearing turbo
  4. Oil Drain - proper size and routing
  5. Water Lines - set up for greatest thermal siphon effect
  6. Charge Tubing - determine diameter for application needs
  7. Charge-Air-Cooler - determine core size for application needs, design
    manifolds for optimal flow, mount for durability
  8. BOV - VTA for MAP engines and by-pass for MAF engines
  9. Wastegate - connect signal line to compressor outlet, smooth transition to
    external wastegate
  10. System Testing - pressurize system to check for leakage, periodically check
    clamp tightness and the condition of couplers
  11. System Monitoring - proper gauges/sensors to monitor engine for optimal
    performance and component durability
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All of this info can be found here as they were the original providers of the info.
Old 07-29-2011, 10:14 AM
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More info need for turbos.

A Look At Twin Scroll Turbo System Design - Divide And Conquer?

Here you can see how a divided...

read full caption

Here you can see how a divided or twin-scroll turbocharger has two separate exhaust gas entry paths into and through the turbine, maintaining the improved scavenging effect and exhaust gas flow achieved by pairing complementary exhaust primaries on the header.

Back in the day, most aftermarket and factory turbocharger systems featured simple log-style exhaust manifolds. But just like on normally aspirated engines, where exhaust manifold design has become recognized as a critical element to maximizing horsepower and torque output, there has been increasing attention paid to turbocharger and turbo manifold design. Divided or "twin-scroll" turbos and manifolds have emerged as the preferred design of many of the top tuners and even OEMs, showing up on high-performance models like the Mitsubishi EVO, Pontiac Solstice GXP and JDM Impreza STI. But what exactly are the differences between single-scroll (or constant pressure) turbo systems and twin-scroll (or two-pulse) turbo systems and how do these design differences impact overall engine performance?

Single-scroll systems have been in use for a long time, and for good reason. These systems are generally compact, inexpensive and extremely durable under the high heat they're exposed to. So from a simplicity of design, packaging and reliability standpoint, a single-scroll, constant-pressure turbo system is quite appealing-especially to the OEMs that must consider more than just power production. Although log-style or simple unequal-length turbo manifolds used by the OEMs can be tweaked for improved performance or replaced by a more sophisticated equal-length aftermarket manifold, this doesn't change the fact that there's a single exhaust gas inlet to the turbo's "hot side" turbine (which powers the "cold side" compressor, force feeding a denser and therefore more oxygen-rich air charge into the combustion chamber from the intake side). Because of this design limitation, single-scroll systems are not particularly efficient at low engine speeds or high loads. This decreased turbine efficiency contributes to turbo lag, something we've all probably experienced while driving a stock turbocharged vehicle.

The advantages of a twin-scroll...

read full caption

The advantages of a twin-scroll turbo system are not lost on the OEMs, many of which are starting to use this setup on their high-performance models, like this newMINICooper S engine.

One of the biggest limitations of most factory single-scroll turbo system is the restrictive nature of its log or compact unequal-length exhaust manifold. Keep in mind, the purpose of this manifold isn't just to channel exhaust gases to the turbocharger's turbine wheel; the manifold must be designed to allow exhaust gases to exit the combustion chamber of each cylinder quickly and efficiently. Also keep in mind that these exhaust gases do not flow in a smooth stream because the gas exits each cylinder based on the engine's firing sequence, resulting in distinct exhaust gas pulses. Next time you fire up your car, place your hand lightly over the exhaust tip (before it gets hot!) and you will feel these pulses. With a log-style or compact OE-style, unequal-length runner exhaust manifold like you'll find on SR20DET or USDM STI engines, the pulse from one cylinder can interfere with subsequent exhaust gas pulses as they enter the manifold from the other cylinders, inhibiting scavenging (where the high-pressure pulse draws the lower pressure gases behind it out of the combustion chamber with it) and increasing reversion (where exhaust gas flow is disturbed so much that its direction of travel reverses and pollutes the combustion chambers with hot exhaust gases). The trapped and wasted kinetic exhaust gas energy from poor scavenging and too much reversion also means higher combustion and exhaust gas temperatures, necessitating less aggressive ignition timing and reduced valve overlap as well as richer air/fuel mixtures (and higher NOx emissions).

Twin-scroll turbo system design addresses many of the shortcomings of single-scroll turbo systems by separating those cylinders whose exhaust gas pulses interfere with each other. Similar in concept to pairing cylinders on race headers for normally aspirated engines, twin-scroll design pairs cylinders to one side of the turbine inlet such that the kinetic energy from the exhaust gases is recovered more efficiently by the turbine. For example, if a four-cylinder engine's firing sequence is 1-3-4-2, cylinder 1 is ending its expansion stroke and opening its exhaust valves while cylinder 2 still has its exhaust valves open (while in its overlap period, where both the intake and exhaust valves are partially open at the same time). In a single-scroll or undivided manifold, the exhaust gas pressure pulse from cylinder 1 is therefore going to interfere with cylinder 2's ability to expel its exhaust gases, rather than delivering it undisturbed to the turbo's turbine the way a twin-scroll system allows.
The result of the superior scavenging effect from a twin-scroll design is better pressure distribution in the exhaust ports and moreefficient delivery of exhaust gas energy to the turbocharger's turbine. This in turn allows greater valve overlap, resulting in an improved quality and quantity of the air charge entering each cylinder. In fact, with more valve overlap, the scavenging effect of the exhaust flow can literally draw more air in on the intake side while drawing out the last of the low-pressure exhaust gases, helping pack each cylinder with a denser and purer air charge. And as we all know, a denser and purer air charge means stronger combustion and more power, and more power is good!

But the benefits of twin-scroll design don't end there. With its greater volumetric efficiency and stronger scavenging effect, higher ignition delay can be used, which helps keep peak temperature in the cylinders down. Since cooler cylinder temperatures and lower exhaust gas temperatures allows for a leaner air/fuel ratio, twin-scroll turbo design has been shown to increase turbine efficiency by 7-8 percent and result in fuelefficiency improvements as high as 5 percent.

Combine these benefits with a well-engineered tubular equal-length manifold and the design strengths of a twin-scroll approach can pay even bigger dividends. "Equal length" simply refers to the length of the primary exhaust manifold tubes or runners that the cylinder head exhaust ports breath out into, which should ideally be of equal length before merging at a narrow angle at the collector so that the gases flow smoothly together into the turbine inlet. This helps maintain exhaust gas pulse energy, resulting in better boost response and overall higher turbo efficiency.

Designing a high-performance twin-scroll tubular manifold like those available from top tuners like Full-Race is no simple task. Fitting equal-length primaries into the tight confines of a turbocharged car's engine bay while maintaining proper radius bends and strong exhaust gas flow characteristics is a serious design challenge. Determining the best length and diameter of the primaries and angle of the merge collector also requires a lot of R&D, as does choosing the best wall thickness and material for the tubing itself. That's where Full-Race's team of highly educated mechanical engineers and years of constant refinement of their designs comes into play. According to Geoff at Full-Race, "Because of the increased turbine efficiency found in twin-scroll systems, twin-scroll manifolds can often use a smaller runner than a single-scroll design. However, due to the complex shape of the runners and the requirement for a second wastegate and dumptube (one for each side of the divided turbine) there's more mass and more parts which adds expense and complexity. Plus, twin-scroll turbos are physically larger than their single-scroll equivalents, so it's more difficult to make them fit our cramped engine bays." Overcoming these challenges means developing extremely robust manifolds that make smart use of the available space, something Full-Race does with the help of computer programs like SolidWorks and other proprietary processes.
All this hard work does translate to serious performance gains in the power-delivery department, particularly at spool-up and peak torque where sophisticated tubular twin-scroll manifolds properly matched to a twin-scroll turbo deliver superior airflow to single-scroll or OE twin-scroll designs. According to Geoff, "Our twin-scroll turbo kits have a higher average cylinder pressure and turbine efficiency, while single-scroll systems tend to have a higher peak cylinder pressure and exhaust backpressure. We have found the twin-scroll systems have higher backpressure at low rpm (which is good for turbo spool-up) and lower backpressure at high rpm (which is good for top-end performance). On the other hand, single-scroll systems have lower backpressure at low rpm (bad for spool-up) and higher backpressure at high rpm (which hurts top-end performance)." In order to realize the full benefit of a top-shelf twin-scroll system like one of Full-Race's, the manifold design and A/R ratio of the turbo must be spot-on, so it's best to get the help of a professional when choosing a turbo for this type of system.

It's certainly possible to generate huge power and great high-rpm performance with a single-scroll turbo system. There are plenty of examples of very high-horsepower, single-scroll turbocharged engines out there, but with single-scroll systems spool-up and response are much slower than with a twin-scroll design, yet twin-scroll systems still provide excellent top end performance. Although switching from single-scroll to twin-scroll can be expensive, for hard-core boost junkies who want much faster throttle response without giving up any top end, there is no better solution. With the added benefits of higher turbine efficiency, lower cylinder temps and EGTs which allow more aggressive timing and fuel mapping, and the freedom to run more overlap,twin-scroll turbo system design is really a perfect match for the high specific output engines featured in many of our favorite sport compact machines.

Sourced from Modified Mag
Link to article provided here
They also use a picture of the Prince motor as an example of Twin scroll turbos.

****NOTE**** Click on the "no photo" and it will link you to pictures of what they are speaking about
Old 02-08-2016, 07:43 AM
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Very comprehensive information and perhaps this will also help:
Mini Cooper Turbo Application Guide
MINI Cooper Turbo Porting Benefits
Industry Leader in MINI Cooper and Classic Mini Parts and Accessories
Open M-F 6am-5pm PT | 800-946-2642 |

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