WTF Tuning Part 2: The Turbocharger 101 & Basic Boost Control
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This is a discussion on WTF Tuning Part 2: The Turbocharger 101 & Basic Boost Control within the Tuning: Electronic Engine Management forums, part of the Tech & Modifying & General Repairs category; General Disclaimer to Start Off You shouldn't blow your car up doing this. Don't make map changes unless you know ...

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    Registered User Heide264's Avatar
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    WTF Tuning Part 2: The Turbocharger 101 & Basic Boost Control

    General Disclaimer to Start Off
    You shouldn't blow your car up doing this. Don't make map changes unless you know what you are doing. If you do, don't blame me. You typed the number in. You flashed it to the car. That being said, I've never heard of anybody doing damage by logging data. Bottom line, as a blanket statement, I'm not responsible for your car. Just putting it out there.


    Introduction
    For this installment, I wanted to actually get into something 'physical'. As you progress and learn more about tuning, you'll find the actual electronic tuning part (with the tables and nerdy stuff) is really just a means to control physical/mechanical equipment. If you don't fully understand the mechanical parts behind it... You will chase your tail in excel sheets one way or another. A good example of that is boost control.

    Most of the fine details concerning turbochargers I learned from Turbo: Real-World High-Performance Turbocharger Systems by Jay K. Miller. It's a great book - I never realized how little I understood about turbochargers until I read that book.

    To start, a turbocharger is one method of supercharging a car - it's a simple concept... Push air into the engine as opposed to pulling it in. Turbocharging tends to be a practical means of doing so - it primarily uses otherwise wasted exhaust heat/energy to compress incoming air for the engine. Other forms of supercharging involve using a mechanical linkage (common supercharger) or chemical injection (nitrous).


    Turbocharger Construction:
    The turbo has three main 'building blocks'. The turbine, the compressor, and the bearings in between. The hard part about the turbo is understanding that both the compressor and turbine must be fit to a given situation. I will go over the Wastegate Actuator (WGA) later in the tread. Just left it there in the pictures for you to note for now.

    Thanks to Zax for the turbo pictures in this post. I took them from him... along with some noods which you can't have.



    Turbine:



    The turbine is one of the two devices you stare at if you take you downpipe off. One being the wastegate (will cover that later), and the little propeller type wheel commonly known as the turbine. As (extremely) hot gases leave the engine, pass into the headers, and through this half of the turbo, the heat and speed of the pulses is transferred into rotational motion. Think of blowing on a pinwheel... then think of using boiling water to spin the pinwheel.

    The turbine properties will greatly effect your end outcome. Too small of a turbine will cause excessive exhaust back pressure on the engine (even before your down pipe)... Too big and it will not 'spool' up in a reasonable amount of time. I'd like to emphasis the first point there - regardless of if you want a fast spooling turbo... too small of a turbine will hurt performance - a lot!


    Compressor:



    On the other end of the shaft from the turbine.. you'll find the compressor. It's important to realize we are now on the other side of the turbo. Instead of this device being between the engine and the down pipe... this one is in between your intake and your engine/intercooler. As expected... the compressor will in fact spin along with the turbine... but it will compress the air in the intake tract of your car and spit the hot gas out to the intercooler.

    The compressor properties will also effect your end outcome. An improperly sized compressor will stall/surge, or be out of its efficiency range (big problem - will cover that later). It's important that both the compressor and turbine match the application!


    Bearing Housing:
    The bearing housing is one of the hot topics now in turbo design. Ball bearing turbos are snatching up the spot light for a good reason. Otherwise, I don't want to dive too far into this. Just know that ball bearing turbos are faster responding and more durable - by a significant margin.


    Okay... Now that we understand the two basic halves of the turbo, there are two related topics to take into consideration - variable geometry & boost control.
    Last edited by Heide264; 09-13-2012 at 12:35 PM.
    Quote Originally Posted by Trainrex
    He was throwing balloons filled with sulfuric acid and shrapnel at the swat team. They finally had to take him down with rubber bullets.
    2011 STi Build Log
    -Part 1 - Reading, Data Logging, and Analyzing Data
    -Part 2 - Turbocharger 101 & Basic Boost Control
    -Part 3 - EcuFlash, Experimental Defintions, and a Drive By Wire Intro

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    Registered User Heide264's Avatar
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    To understand a bit about variable geometry (RE: Wastegates)... it helps to understand the history of 'the snail'. I'm not a historian, however, so you'll get a nutshell version.

    Extra Stuff / Nerd Talk:
    Turbos came about due to diesel & airplanes. Shocker... it wasn't designed by Subaru. The turbos were originally designed to run at steady state. I'm going to pick up where the turbo started to be used by ground based diesel engines. Diesel engines are great for turbos - they provide a much needed boost of airflow into the engine without excessive cams. The other 'not-so-common' reason they are great for diesel engines is due to the limited operating range of diesel engines. For example - a generator runs at one RPM. A diesel truck runs over half the rpm range of a petrol truck. You get the idea. They could pick a turbine... pick a compressor... smack them together and you have a great efficiency boost. The issue comes about when the turbo needs to be 'responsive' or run over a wide range of airflow.

    If you really look into a given turbine and compressor... you should realize that the turbo itself is somewhat 'unstable'. The more air that the engine puts out... the faster the turbine spins... faster the compressor spins... and the more air that is forced into the engine. See the issue? You must pick a turbine and compressor combo that is STABLE. The problem with that, is that you must size the turbo to a given cfm - easy to predict with a diesel engine that will run at a given airflow for 90% of its life and doesn't need to be responsive. When dealing with petrol engines... you want to be able to allow the turbo to speed up or slow down given a certain set of circumstances.

    So... Variable geometry turbos enter the game. The idea being you could change the way the turbine acts. You could have the turbine act as a smaller turbine for low air flows to get the thing spinning (Think porshe turbos)... or the turbine act smaller to vent excess pressure (*cough, wastegate, cough). Variable geometry really opened up the world of turbocharging to petrol powered engines. It allowed a system to hit 'full boost' by 3k rpm and then not shoot a piston at 6k rpm. Or... it allowed a turbo that was sized to run at full load 5k rpm to maybe scale itself down and be more responsive.

    Important stuff:
    If you aren't familiar with the waste gate, it is simply a hole placed in parallel or beside the turbos turbine. There is a small spring loaded flapper that covers the hole normally - forcing all the exhaust energy through the turbine. As the pressure against the flapper increases (or the spring pressure holding the flapper shut decreases), it pushes the flapper open and allows exhaust energy to go around the turbine (and not speed the compressor up).

    To put it another way... the waste gate on your turbo is a way of creating a variable geometry turbo which you can actually control! Even if it is just a small hole with a flapper that covers it.
    Last edited by Heide264; 09-13-2012 at 12:37 PM.
    Quote Originally Posted by Trainrex
    He was throwing balloons filled with sulfuric acid and shrapnel at the swat team. They finally had to take him down with rubber bullets.
    2011 STi Build Log
    -Part 1 - Reading, Data Logging, and Analyzing Data
    -Part 2 - Turbocharger 101 & Basic Boost Control
    -Part 3 - EcuFlash, Experimental Defintions, and a Drive By Wire Intro

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    Registered User Heide264's Avatar
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    So, we've established WHAT you are controlling and HOW boost can be controlled. From here out, it's important to understand those core ideas. Your ECU doesn't just drop boost. Your boost solenoid doesn't magically turn the turbo off. You may not have realized it, but you already understand HOW boost is controlled. The wastegate is opened or closed. The WG is the only form of direct physical control you have regarding your turbo.

    That being said - there are some fantastic ways to control that wastegate. I will go over the stock setup, a similar setup using a common aftermarket boost control solenoid, and a setup using a manual boost controller. I may throw in a brain teaser at the end for those of you who are smarter than zachary and I .

    Key Terms:

    Waste Gate (WG) - This is a hole of some sort that allows air to bypass the turbine. This is the physical hole as well as the immediate 'cover' - lid/flapper/etc. In the case of the stock setup, its beside the turbine in the turbo. In an EWG setup, it is located on the up pipe and the stock one is welded or secured shut.

    Waste Gate Actuator (WGA) - Slight terminology difference here. The actuator is what opens or closes the wastegate. It is normally a pressure sensitive diaphragm (spring loaded) that somehow controls the waste gate. In the stock setup, the spring pushes on a small lever that twists the wastegate open or closed. In an EWG, the lever is eliminated and the diaphragm directly opens/closes the wastegate.

    Manifold Pressure / High Pressure (HP) - Seems simple enough. It gets confusing when going over boost control schemes. This is your current manifold/boost pressure. Think of it more as a 'signal' than anything else. This will be altered by either your manual boost controller or your electronic boost control solenoid, and then sent to one side of the waste gate actuator under normal circumstances. This is normally taken directly off the turbo compressor outlet.

    Intake/Low Pressure (LP) - Low pressure 'reference' - normally a port off of the intake post MAF reading. This is used similar to a ground or reference in an electronic circuit. Your manifold pressure is generally useless without comparing it to the LP reference.

    Electronic Boost Control Solenoid (EBCS) - This is one of the two main instruments commonly used in boost control. There are two forms of it, the stock '2-port' bleed type, and the aftermarket '3-port' interrupt type. I will go over the differences more below in each situation. Keep in mind that EBCS work on a 'pulse width modulation' (PWM) type principal - everything is in frequency and duty cycle.. not just on and off.

    Manual Boost Controller (MBC) - This is the common alternative to an EBCS. It is normally a spring loaded diaphragm that opens at a given pressure differential, which is adjustable by a small manual knob. These will be explained more below.


    Boost Control Setups:

    All setups will include a brief artistic rendering, possibly a photo, and an explanation for each. It's important that you understand the specifics behind your system - otherwise you will NOT understand how your ECU deals with it. Worth noting is that there are many ways to deal with boost control systems. These are just the common ones I've found. Once you understand how they work, you can piece together custom ones to benefit your particular case.

    Big thanks to this link by Jeff Perrin. Not only do I recommend reading it, it helped me through several sanity checks while making up these diagrams. You'll find much of the information below in that article... in a nicer and more conclusive form.


    Stock Setup:


    Ah, yup. Here is the starting block. The stock system. It uses a '2-port' EBCS. The HP and WGA are T'd together... and the stock solenoid opens to 'bleed' off the pressure. When the solenoid is fully active (100% duty cycle), it allows all of the air to flow through the solenoid and into the low pressure area - and hence trick the wastegate into seeing less pressure. Since the wastegate stays closed until the WGA sees a pressure above its spring pressure (normally 7psi), it will stay shut and allow the turbo to continue building boost. Once the WGA sees over 7psi.. the waste gate will open up. This is counter intuitive to what you would expect - always remember this is a BLEED type system. The solenoid actively has to bleed pressure away from the WGA to allow the car to build boost.

    This method is normally effective. It has a restrictor pill and isn't a very dynamic system. The other downside, is that the solenoid can not isolate the wastegate from the HP source - which may slow spool down between WGA spring pressure and max boost pressure. Hence, the 3-port opens the scene.


    3-port EBCS Setup:


    Ahh, that looks better. No more T. No more restrictor pill. The 3-port EBCS is much faster than the stock bleeder, and adds another important perk... The ability to completely isolate the WGA from the HP source regardless of boost pressure. This can be dangerous if you aren't careful. Note that at zero percent duty cycle, the solenoid will allow the WGA to see the HP source completely. At 100% duty cycle, the WGA is completely isolated.

    While tough to tune, the 3-port does allow for a quicker spool up. It should, in theory, spool as fast as a MBC due to being able to completely isolate the WGA (it won't, but should be close). Expect your turbo dynamics (later) to change due to this, on top of your initial waste gate duty cycles. It allows for a more dynamic and accurate system, especially during spool up. They aren't easily tuned unless you understand the boost control system well.

    This is the setup I currently run. The newer ECUs allow for some pretty advanced control of the EBCS. One perk I have learned though, while on the track, a MBC would not have worked for me as well. I found that I had to run my lower boost map actually. While having close to mechanical spool up is a lot of fun for daily driving, you'll find it can be quite challenging & scary when rolling on the throttle around a bend.


    MBC Setup:


    Yup. Let that soak in. That's how easy it is. With this approach, you remove boost control from the ECU completely. The ECU now has no direct way of controlling the WG. The MBC is a simple device. It has it's pro's and con's. Main pro, it is much easier to tune. The largest con, in my opinion, is that you have pulled the boost control from the ECU. I like to 'taper' my boost much more sharply than a standard MBC setup will allow (EG: 20psi at 3k... 14psi at 6k). This is important to allow the turbo to stay in it's efficiency zone. Remember, the turbo in a petrol car needs controlled. Otherwise it will turn into a useless hair dryer - 20psi at redline is not going to produce more power than 14psi on the stock turbo due to a sharp drop off in efficiency at that volume.

    Still, mechanical spool up on a car is fast and fun to drive. It is a viable method of boost control.


    Hybrid MBC/EBCS Boost Control


    Here's your extra credit. This setup when properly installed and tuned, should give you pros of both a MBC and an EBCS. It requires an in depth understanding of the boost control system to install correctly, and more importantly, tune safely. Routing vacuum lines incorrectly is a quick and easy way to shoot pistons out the block.

    I am personally looking to switch over to a similar setup sometime. This will give you mechanical spool up when under full throttle, and allows the EBCS to taper boost off as RPMs increase or throttle decreases. There are many games you can play with the ECU to make this approach extremely fun. This setup also gives you a bit of a safety blanket if either device fails. Also, it makes for an easy valet mode if you run the MBC control into the cabin.

    For more information and some extra nerd speak, check out this link. Thanks to Matt for pointing this one out.


    Summary on Boost Control Setups:
    Looking at that hybrid setup, you'll start to realize that boost control is not an 'easy' subject. While it is basic at first, you need to understand COMPLETELY how your boost control setup works. You need to be able to understand what will happen at 100% WGDC, 0% WGDC, or if WGDC even matters. Once you grasp that concept - you'll probably get twisted up anyhow even on the easier setups. Understanding how the system works though will yield huge results in your cars ability to perform at wide open throttle (WOT) while still being enjoyable at part throttle and cruise... and be a safe and nasty competitor on the track.
    Last edited by Heide264; 09-13-2012 at 12:44 PM.
    Quote Originally Posted by Trainrex
    He was throwing balloons filled with sulfuric acid and shrapnel at the swat team. They finally had to take him down with rubber bullets.
    2011 STi Build Log
    -Part 1 - Reading, Data Logging, and Analyzing Data
    -Part 2 - Turbocharger 101 & Basic Boost Control
    -Part 3 - EcuFlash, Experimental Defintions, and a Drive By Wire Intro

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    Registered User Heide264's Avatar
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    Efficiency:
    Yup. It had to come up. To start, check out a google search on compressor maps. Its important that you take a look at a few of these to understand why it's so important to control your boost appropriately - not just off what numbers you think are best.

    Some compressors only are efficient at certain pressure differences (eg: 2x ratio or 28psig or whatnot). This is much more important than you may realize. While you have a GT35R and your tuner said he'll run "a conservative" tune on it until you build your block... you aren't in the efficient area for your turbo. It's blowing hotter air than it should, wasting more energy, and the system is NOT happy and responsive. Some turbos just like to run at 35psi at medium CFMs. Some turbos like to run at a higher CFM at 25psi. It's just how it works. Research your turbo before you buy one. A lot.


    So what psi I should be targeting?
    Age old question. You should get a rough idea of your engines pumping volume... compare it to a compressor map... and figure out where the turbo will be efficient for your motor. On the flip side, the car may make more power even when the turbo isn't at peak efficiency - especially with a decent intercooler. Regardless, this is not a topic to approach lightly. There is a decent amount of math involved, and (in my opinion) some fairly hefty assumptions. For a common turbo, I would suggest looking dyno databases from reputable tuners to get a good ballpark guess.

    I am currently working on a project to measure turbo efficiency in real time. It will involve taking both pressure and temperature readings pre and post turbo compressor. I will make sure to post up my findings if I ever finish it.


    The ECUs part in this
    I've left out the actual ECU controls until now. I have pointed out where it comes in to play though - controlling your EBCS. Much as you have several components for boost control (EBCS, 3 pressure inputs, ECU input) with one output (the WGA), your ECU takes in many different factors to output just a single WasteGate Duty Cycle (WGDC) to your EBCS.

    I'm not familiar with older ECUs, but as far as the newer drive-by-wire cars... Even finding your target boost can be a headache. It's not easy. Your tune has a few tables in it to govern drive-by-wire details. The important one for boost control is normally just "requested torque". Your base WGDC tables have an axis for requested torque and one for RPM. Older cars use throttle opening and I believe engine load.

    The nice thing about having the ECU control your boost, is that it can make sure it's right on the dot. The ECU has a PID (proportional, integral, and differential) control system... minus the differential part. This allows your ECU to make slight changes to the boost control solenoids output to make a closer match to your 'target boost'. The coefficients for the controls can be changed, and are commonly called your turbo dynamics (TD). There is one table for proportional, and one for integral. I can't explain PIDs here, but, these will be / should be changed when you change your boost control system (3-port vs 2-port, EWG vs normal WG) to allow the system to react as it should.

    This is a complicated topic, and I've found tuning these coefficients is a frustrating process to learn. If you have a background in PID controls, it is a great practical example of them.



    This about wraps up the thread topic. I want to go back and add some pictures in as time goes on. In the mean time, feel free to discuss or pitch in any feedback.
    Last edited by Heide264; 09-11-2012 at 01:58 PM.
    Quote Originally Posted by Trainrex
    He was throwing balloons filled with sulfuric acid and shrapnel at the swat team. They finally had to take him down with rubber bullets.
    2011 STi Build Log
    -Part 1 - Reading, Data Logging, and Analyzing Data
    -Part 2 - Turbocharger 101 & Basic Boost Control
    -Part 3 - EcuFlash, Experimental Defintions, and a Drive By Wire Intro

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    Excellent. Subscribed!
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    Registered User speedtown's Avatar
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    good reading thanks a lot

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    Master Baiter EJ257's Avatar
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    We should probably at least touch on the hybrid boost control setup:
    new hybrid mbc/ebc method of boost control - NASIOC

    Use an MBC for everything WOT, while allowing the ECU control part-throttle / failsafes via the EBCS. Pros of both, cons of neither.
    2005 WRX STi (Mods | Virtual Dyno)

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    UNYSOC

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    indeed... subscribed!

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    Registered User Heide264's Avatar
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    Re: WTF Tuning Part 2: The Turbocharger 101 & Basic Boost Control

    Quote Originally Posted by EJ257 View Post
    We should probably at least touch on the hybrid boost control setup:
    new hybrid mbc/ebc method of boost control - NASIOC

    Use an MBC for everything WOT, while allowing the ECU control part-throttle / failsafes via the EBCS. Pros of both, cons of neither.
    Will do. Was planning on making that my brain teaser .

    EDIT: Updated!
    Last edited by Heide264; 09-12-2012 at 04:11 AM.
    Quote Originally Posted by Trainrex
    He was throwing balloons filled with sulfuric acid and shrapnel at the swat team. They finally had to take him down with rubber bullets.
    2011 STi Build Log
    -Part 1 - Reading, Data Logging, and Analyzing Data
    -Part 2 - Turbocharger 101 & Basic Boost Control
    -Part 3 - EcuFlash, Experimental Defintions, and a Drive By Wire Intro

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    Registered User Heide264's Avatar
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    Updated to include nudes/pics and a few minor format tweaks
    Quote Originally Posted by Trainrex
    He was throwing balloons filled with sulfuric acid and shrapnel at the swat team. They finally had to take him down with rubber bullets.
    2011 STi Build Log
    -Part 1 - Reading, Data Logging, and Analyzing Data
    -Part 2 - Turbocharger 101 & Basic Boost Control
    -Part 3 - EcuFlash, Experimental Defintions, and a Drive By Wire Intro

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    Heide264 thank you for the links...

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