*Turbocharged Motors* - Understanding the Components, Processes and Modifications - Subaru WRX Forum
 
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#1 Old 12-27-2008, 10:08 PM
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*Turbocharged Motors* - Understanding the Components, Processes and Modifications

A DISCLAIMER BEFORE WE BEGIN: This post is intended to help individuals understand Turbocharged engines. Though it may initially seem like an intimidating topic to some of you, I ask for your patience and open-mindedness. Just 6 years ago, I knew NOTHING about turbochargers or how they worked. It took many explanations and several different illustrations for me to understand. And even then, I wasn't completely comfortable with the process... It took a proper and patient explanation to completely sink in. Though turbocharging has become somewhat of a common process, I will be focusing on the 2.5L Boxer motor. Without getting too specific, I intend to introduce and describe the task and importance of each of the key components in the power plant. I will also cover some possible restrictions in the stock setup and go over potential modifications. This post will be here... Take it one bite at a time, and chew on it. I broke it down, so it's easier to digest. Take your time, learn the components, their duties, and soon you'll be addicted to it as much I am. So without further ado, let's get started.

What's A Turbo? - Essentially, a turbocharger is a unit that effectively compresses air on the compressor side thanks to the exhaust gases of the engine spinning the turbine side. Compressed air is highly pressurized air in a small area (pounds per square inch). Theoretically, the more psi an intake system delivers to the combustion chamber, the more fuel will be delivered to keep a safe Air/Fuel ratio. The stronger the combustion, the more power you make. Bear with me, it gets simpler. Assuming your ecu and fuel system are doing their job to compensate for changes, then the following is true: More Air = More Power.

Let's first take a closer look at the compressor itself. Here is an illustration that I found on the web. Credit to Jim Hatch for this excellent rendition that I modified to make more beginner-friendly.

What Makes Up A Turbo? - The anatomy of the unit may appear intimidating at first. It's really quite a simple contraption. Let's break it down. So the unit consists of two chambers. Each one houses a 'fan blade' set-up internally. These two fans are connected by the rotator shaft. So if one is forced to turn, the other will obviously turn at the same rate. So about those two chambers:

THE TURBINE (EXHAUST) SIDE - Exhaust gases enter via the Up-Pipe to turn the fan blades and exit out the Down-Pipe.

THE COMPRESSOR (INTAKE) SIDE - Air is pulled in by vacuum pressure and compressed from the Intake. Exits to the Intercooler.

Intake Fan. Exhaust Fan. Attached with a Shaft. Ok, Got it! So How Does A Turbo Compress Air? - Assuming you're familiar with the way standard engines work, let's fast forward to post-combustion, when exhaust gases travel down the headers (or exhaust manifolds). In a Naturally Aspirated car, this is where your exhaust system begins... In a turbocharged engine, this is where Boosting Begins. The gases are routed from the manifold via the Up-Pipe into the EXHAUST SIDE of the turbo. The gases spin the fan blades VERY rapidly, I'm talking tens of thousands of RPM.

So if the Exhaust Fan is spinning, and its connected to the shaft... Then what else is spinning? That's right, the Intake Fan! The high-speed rotation of the Intake Fan creates a vacuum, which literally sucks air in form the intake, compresses the air, and sends it off to the Intercooler.
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So with this basic knowledge of how the turbo makes power, let's take a broader look at the process as a whole.

I've designed a diagram of the power plant with great emphasis in trying to keep it as Simple and Uncomplicated as possible. I do hope I've accomplished this effectively.


This diagram is spread and some components may not be in the exact location, but they are correctly placed if you follow the path. I did not diagram it out 100% like the stock system, because things are stacked and wouldn't be as easy to understand.

As I identify each component as the air passes through it, I will also note any possible restrictions and touch slightly on possible modifications. We should find ourselves more familiar with the turbo process once we exit the tailpipe. Starting at the upper left of the diagram, let's begin:

AIR-INTAKE SYSTEM:
What Does It Do? - Draws air in from the front of the vehicle.
Any Restrictions? - Yes. During full throttle, air is being pulled in very aggressively. The stock setup MAY have trouble pulling air efficiently during this demanding moment if you're pushing tremendous power. Also, narrow diameter hoses pose as a restriction, as do ribs, corrugations and bends that create turbulence and slow down the overall air flow.
What Can Be Done To Help? - There are already several Cold Air Intake options available. But please be cautious with this modifications. These intake systems are typically good enough until you read higher horsepower levels. Also, these aftermarket units CAN have an adverse effect on your engine. Most make their power by creating lean conditions that force your ECU to demand more fuel, and so you make more power. But unless properly tuned for, your ECU will eventually adjust your AFRs and while your vehicle will run safer, the gains will also lessen.

TURBO INLET HOSE:
What Does It Do? - Routes the air from the Intake to the Turbo Chargers Compressor Side.
Any Restrictions? - Sure, it can. If the stock inlet hose is narrow or ribbed, it can create a disturbance in the efficiency of flow of air into the turbo.
What Can Be Done To Help? - Silicon Inlet hoses generally offer a smoother air path that will allow the turbo to spool a few hundred rpm earlier. Try looking for a reinforced unit that will not collapse under boost.

--At this point, the air enters the turbochargers Intake Side. While the air is compressed and pushed out, it also gets hot due to the naturally high temperature operation of the turbocharger itself. The air then enters the next component: The Intercooler.

INTERCOOLER:
What Does It Do? - Cools the hot air pushed from the turbocharger, making it more dense and suitable for effective combustion.
Any Restrictions? - Sure. An intercooler can always be improved to a more efficient unit. Is it necessary? It's arguable at stock power levels, but it's important to note some of the weaknesses. The factory Intercooler has plastic end tanks. It has been documented that end tanks have failed by cracking, leaking, or blowing out at higher than stock levels of boost. Of course, Subaru intended the vehicle to run stock boost pressures, so to call it a design flaw would be a mistake. But if you plan on regularly running higher boost pressures, please make this modification a high priority.
What Can Be Done To Help? - A larger core unit with cast end tanks or one thats placed as a front mount can effectively reduce temperatures and prevent heat soak. Keep in mind that flow properties also play a role here. So when selecting an intercooler, be aware of its flow characteristics more so than its size. Also, heat soak is only an issue when heat rises from the motor and the intercooler is not receiving any air to cool down. Thankfully, our intercoolers are placed somewhat behind the engine making it less prone to heat soak. And once moving, the factory unit cools very effectively via the hood scoop.

--The air is then routed to the Intake Manifold. The Intake Manifold dumps the air into the Engine. Inside the Combustion Chamber, combustion occurs, depositing exhaust gases out of the Exhaust Manifold, or Header.

--The 2.5L WRX's header has a fairly unrestrictive and catless Up-Pipe(nice!), which really wouldn't benefit from replacing, unless you're running a huge turbo setup. The gases are then pushed into the Exhaust Side of the turbo and turn the fan blades rapidly creating a vacuum(boost) on the Intake or Compressor Side (The process simultaneously continues on from the Intake Side). The gases then exit the turbocharger and dump into the next component.

DOWNPIPE (Sections A & B):
What Does It Do? - Routes exhaust gas from the turbo down to the exhaust system. Section A is essentially the Downpipe itself, and Section B may be referred to as the Secondary Pipe, or Test Pipe.
Any Restrictions? - Absolutely! On the Stock setup, there is one catalytic converter on the 1st section and another on the second. Aside from the cats, it's narrow and mangled design doesn't create a good opportunity for the gases to flow out freely and in turn create BACK PRESSURE. Back Pressure, is essentially caused by a 'clogging' or restricting of the flow of exhaust gases. This inhibits the fan on the exhaust side of the turbo to spin freely. So the turbo is working harder and making less power. A simple example: Take a narrow coffee mixer/straw, bend it in a few places, seal your mouth around it and blow hard. Feel the pressure exiting the other side... Not much right? Now take a regular diameter straw bend it conservatively and now blow. This demonstrates that a narrow, restrictive straw will make you work harder to blow a specific amount of air, while a freer flowing, larger diameter straw lets you blow with greater efficiency without blowing as hard. The EXACT same applies to Turbos. The easier the air exits, the easier the blades spin, the easier you create that boost.
What Can Be Done To Help? - A replacement of the entire Downpipe is what would be recommended. I recommend keeping one Cat, only because I prefer to run a cleaner, not-so-loud, non-smelly car. This does not mean keeping a stock cat. There are race-cats(or high flow cats) available with most Downpipe systems. At full throttle, a race-cat poses no measureable flow-restriction over a catless design (we're talking MAYBE 1 hp). There will be different designs to choose from: Bellmouth or Divorced Wastegate. It's a whole different topic to discuss. However, both will offer a huge gain over stock, and neither will pose as a restriction. Also, the slight amount of backpressure that a high flow cat may create at lower revs will actually serve as a benefit, maintaining good torque figures down low by allowing a continuous pulse of exhaust gas rather than an emptied out and refilled effect which can kill torque.

CAT-BACK EXHAUST SYSTEM
What Does It Do? - Continues to guide the exhaust gases collected from the Downpipe out the Tailpipe.
Any Restrictions? - Sure. You wouldn't want a coffee straw at the end of your regular straw would you? Again, a case of reducing backpressure. It's highly recommended that this be opened up.
What Can Be Done To Help? - There are several to choose from in the aftermarket. They will mostly all be 3 inch with mandrel bent pipes, which mean the diameter does not narrow during the bends and poses no restriction. Any 3 inch cat-back is a 3 inch cat-back, choose the sound you like best. As long as they are equipped with straight-flow mufflers, there will be no power difference worth mentioning.
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Congratulations! You got sucked in as air through the intake, got compressed by the turbos intake (compressor) side, got cooled by the intercooler, and combusted in the engine. Then you left the engine as exhaust gas, ran through the turbos exhaust (turbine) side to help create more boost, then left the turbo through the downpipe, through the catback, and out the tailpipe!

Again, I understand that this is a LOT of information. But I hope I've been able to deliver it in a more understandable manner. One that involves YOU in the process and guides you through each component. I also covered some possible restrictions and the modifications that would alleviate these restrictions to help create a more efficient turbocharged experience.

But there is one last thing I would like to mention, and that's the importance of engine management.

We now understand that we can allow the turbo to pull air easier by cutting down on certain restrictions from the intake end and exhaust end. But there's one important thing to keep in mind. Every flow measurement (air, fuel, timing, boost, etc...) is constantly being monitored by the ECU. It is programmed to run at specific Air/Fuel ratios. So if you INCREASE the air coming in and assume its leaning out. Yes, it is, slightly... But the ECU will eventually correct itself once it detects an out-of-norm ratio, or a knock. This is why people are often told to RESET their ECU after adding a modification. So as soon as you punch the throttle, you will feel a VERY notable difference... but as time goes on, that ecu will have retarded timing and adapted to the change.

My advice is simple: Each mod you add mentioned above will give you a gain. How much of a gain is to be taken with a grain of salt. Dyno's show an immediate pull, not an adapted pull. Take horsepower and torque graphs for what they are, but do not expect these gains to add up perfectly. Overtime these parts that you spend money on will no longer do what they used to, because your ECU will not allow it. Just because an intake is CAPABLE of drawing more air in, doesn't mean it will.

To get the MOST out of your mods, or even the most out of your vehicle in stock trim, invest in a good Engine Management option. This will allow you to run tunes SPECIFICALLY designed to work with components that allow a freer flowing exhaust, intake, etc... In other words, you will ACTUALLY be running a leaner map and taking full advantage of your mods, while maintaining stock-like reliability. I don't want to name drop, but there's a plethora of options out there! And since this is an informational thread, I've tried my hardest to keep Brand Names out and Information in.

At this point, with the information I've provided, you should be able to decipher a good mod from a not-so-good one. You are now equipped with a basic understanding of turbocharging. You don't need dyno graphs or companies to tell you that something will give you a gain. All you need is your logical understanding to simply determine whether or not a specific mod will truly make this process more efficient.

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I truly would like to thank anyone who spent the time to read this post as it took a lot of dedication and effort to plan, illustrate, write, and complete. It's near impossible to get it right the first time, so if anybody notices anything that needs correcting, please let me know and I will correct it immediately.
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#2 Old 07-19-2009, 07:41 PM
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Can somebody please sticky this?
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#3 Old 07-19-2009, 08:07 PM
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Good job. btw in the PM I meant Intercooler.
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#4 Old 07-19-2009, 09:25 PM
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Thanks Boost Addict. Could you go into some details about waste gate and blow off valve?
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#5 Old 07-20-2009, 01:49 AM
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Originally Posted by rexcellerate View Post
Thanks Boost Addict. Could you go into some details about waste gate and blow off valve?
There you go:
*Blow Off Valves* - The Basics of Blow Off Valves, Bypass Valves & Hybrid Valves

post any questions you may have.
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#6 Old 07-20-2009, 12:02 PM
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You should add more explaining how turbos add power. That's usually where people get lost. Air = power is a good start, but people kind of miss the point. It's really air density in the piston. This is related to flowrate, more specifically:
1) Compression Ratio
2) Pressure (both atmospheric and forced induction)
3) Temperature
4) humidity (and other air components like pollution, etc)

Engines make power by igniting air. You increase air by increasing the flowrate, increasing the pressure, decreasing the temperature (air density increases as temperature falls), filtering out particulates, etc.

This means that when you're talking about intercoolers, you should stress that their purpose is to drop temperatures while maintaining both airflow and pressure thus increasing density to the cylinder. A properly sized intercooler can handle the heat but is not so large as to cause a pressure drop or delays in airflow that act like flow restrictions.

In talking about the turbo itself, it's important to understand the role that temperature plays. It is effectively a heat pipe. A device that works on thermal potential. Basically, it works more efficiently when the hot side is hotter and the cold side is colder.

Also, it would be good to mention that although air = power, you need to adjust fuel and timing to utilize it. Simply stuffing more air inside won't fix anything. In small engines sucking in a lot of air, you may need to change fuel sources in order to ignite them properly (higher octane gas changes ideal ratios and gives more air igniting potential. Additives like meth and nos effectively raise octane too) and adjust the timing of the fuel injection cycle.

PS: I'd also try to talk more generically without getting into specifics of your car. People get confused with the specifics you bring up when they try to apply them to different setups.

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#7 Old 07-20-2009, 01:15 PM
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Originally Posted by mosc View Post
You should add more explaining how turbos add power. That's usually where people get lost. Air = power is a good start, but people kind of miss the point. It's really air density in the piston. This is related to flowrate, more specifically:
1) Compression Ratio
2) Pressure (both atmospheric and forced induction)
3) Temperature
4) humidity (and other air components like pollution, etc)

Engines make power by igniting air. You increase air by increasing the flowrate, increasing the pressure, decreasing the temperature (air density increases as temperature falls), filtering out particulates, etc.

This means that when you're talking about intercoolers, you should stress that their purpose is to drop temperatures while maintaining both airflow and pressure thus increasing density to the cylinder. A properly sized intercooler can handle the heat but is not so large as to cause a pressure drop or delays in airflow that act like flow restrictions.

In talking about the turbo itself, it's important to understand the role that temperature plays. It is effectively a heat pipe. A device that works on thermal potential. Basically, it works more efficiently when the hot side is hotter and the cold side is colder.

Also, it would be good to mention that although air = power, you need to adjust fuel and timing to utilize it. Simply stuffing more air inside won't fix anything. In small engines sucking in a lot of air, you may need to change fuel sources in order to ignite them properly (higher octane gas changes ideal ratios and gives more air igniting potential. Additives like meth and nos effectively raise octane too) and adjust the timing of the fuel injection cycle.

PS: I'd also try to talk more generically without getting into specifics of your car. People get confused with the specifics you bring up when they try to apply them to different setups.
This should explain why certain things are left out:

Without getting too specific, I intend to introduce and describe the task and importance of each of the key components in the power plant.

And in reference to your 'more air = more power' concern:

Assuming your ecu and fuel system are doing their job to compensate for changes, then the following is true: More Air = More Power.

It's all in there for those that take the time to read it. Of course it's not every single thing one can learn about turbocharged motors but it's a good start that a lot of individuals can benefit from.

And in regards to generalizing it and not being specific, this is the 2.5L section, and that's exactly what's being discussed here. Am I missing something?
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