Turbocharging

 

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Using a Turbocharger to Give a Small Engine Big Muscles!

For many years, I've been fascinated with the way that a turbocharger can transform an otherwise ordinary engine into a powerhouse!  Take for example the lowly Ford 2.3L engine which dates back to the 70's and 80's.  Heavy cast iron block topped with a simple 2 valve cast iron cylinder head.  This engine is far from high tech - especially by today's standards!  Yet, this simple and crude engine design has been known to produce some impressive power outputs.  How about 400hp from what basically amounts to a turbocharged 4 cylinder Pinto engine!  Speaking of Pintos, the Ford 2.3 gained a bit of hot rod fame back in 1999 when Hot Rod magazine featured Joe Morgan's turbocharged 2.3 powered Pinto which runs in the 10's in the quarter mile.  This is surprisingly fast powered by an engine that was surprisingly stock.  As you might be able to tell, I have had an interest in the Ford 2.3.  That's because I owned an 87 Merkur XR4Ti that was powered by the Ford 2.3 turbo, and I spent a fair amount of time working on this engine.  But that's not the only experience that I've had with turbochargers.  Below is a list of some of the turbocharged vehicles I've owned (or still do own):
  • 1987 Merkur XR4Ti with Ford 2.3
  • 1992 Eagle Talon Tsi with legendary 4G63
  • 2000 Ford E350 with Powerstroke 7.3L turbodiesel
  • 2005 Kubota M9000 tractor (hey, it's still turbocharged)
  • 2008 Joyner Sand Spider Dune Buggy with aftermarket turbocharger   

Most of the experience I gained was while working on the Merkur XR4Ti years ago.  That was my first turbocharged vehicle.  I had 3 different turbochargers on that engine (stock T3, modified T3, and a hybrid T3/T4).  After an experiment with water injection in which I was spraying into the inlet of the compressor, I ended up with eroded compressor blades.  When I discovered the damaged compressor wheel, it also seemed that the bearings on my stock T3 turbo had excessive play, so I decided it was time for a rebuild.  I sent my stock T3 turbocharger off to Turbonetics to have them rebuild it for me.  Since my stock compressor wheel was damaged, I took the opportunity to upgrade to a bigger compressor wheel out of a Buick Grand National turbocharger.  Turbonetics machined out my stock T3 compressor housing to match the bigger wheel and this is how I ended up with a modified T3 on my engine.  Below are some pictures showing this turbocharger.  The image on the right shows a comparison between a stock T3 compressor wheel and the larger GN compressor wheel.

Modified T3 Compressor Wheel

Modified T3 Turbocharger with Bigger Grand National Compressor Wheel

As is often the case when the power bug bites, I was soon looking for more boost and more power.  The result of that search was another quality Turbonetics product.  This time, I decided to go much bigger with a T3/T04E hybrid turbocharger.  On the T3 turbine side, I chose to go with a 0.63 A/R (aspect ratio).  This provided less restriction and more exhaust flow through the turbine side.  My stock T3 turbocharger came with a 0.48 A/R turbine housing which gave quicker spool up at the expense of additional restriction to flow.  The aspect ratio is something that can be used as a tuning aid for your particular engine.  Larger aspect ratios allow exhaust gases to flow out more freely, but they that also means that more of the exhaust bypasses the turbine wheel.  This means that the turbocharger will be slower to build boost.  This sluggishness to build boost is sometimes referred to as turbo lag.  With the T3 turbine side, the options for A/R's include 0.48, 0.63, 0.82.  Those are the ones that I know about at least.  There may be others.  The A/R of 0.63 on the turbine side seemed to be a good compromise for what I wanted.

Hybrid T3/T04E Turbocharger

Hybrid T3/T04E Turbocharger from my Merkur XR4Ti

On the compressor side, that's where things got much bigger with this hybrid turbo.  Instead of being limited to a small T3 compressor wheel, this hybrid turbo came with an entire T4 compressor side.  In case you didn't know, the T4 is a bigger family of turbos found above the T3 line of turbochargers offered by Garrett.  To complicate things a bit, there are T04B and T04E compressors.  I went with a T04E 50 series compressor side.  I did some studying of turbocharger mapping for the different T04E family of compressor wheels.  The 50 series had an impressive looking map for what I wanted.  Not to get overly complicated, but in the compressor map below, the horizontal axis is the amount of air flow going through the turbocharger.  The veritical axis is the pressure ratio (obviously related to boost pressure).  You want to target a turbocharger compressor which not only operates in an efficient area of the map, but also within a safe zone where you are not at risk of surge.  Surge is a harmful situation where the turbo is trying to flow more air than the engine can handle at that moment.  A situation like this can occur if you are building too much boost at too low of an engine RPM for that particular compressor.  In effect, the airflow stalls and there are shockwaves that flow back through the compressor, and these shockwaves can put unnecessarily stress on a compressor wheel.  So, in the example of the T04E 50 series compressor map below, you would want to make sure that your turbo would operate to the right of the surge line at all times.  To just put it plainly, the 50 trim compressor is much more forgiving than many other compressor sections.  It offers a great balance of ultimate flow capability and also resistance to harmful surge.  A 50 trim T04E compressor can easily support over 400hp worth of air flow.  This particular T3/T4 hybrid turbo with the 50 trim compressor is a great match for many different high performance 4 cylinder engines.  I was very happy with it boosting my Ford 2.3L, and it turned out to be a great match for my engine.  

Turbo Map 

Just slapping a turbocharger onto an engine will not make any more power.  In fact, you'll make less power and likely ruin your engine.  A turbocharger is literally an air compressor.  More specifically, a turbo is a centrifugal air compressor that pumps more air into your engine.  More air without more fuel will not do any good.  It is the fuel burning that produces the power.  More fuel will not burn unless you provide more air (oxygen) for combustion.  When adding a turbocharger, you need to supply the additional fuel to match the additional air.  Too little fuel, and you risk blow torching your engine.  If you've ever used an oxy-acetylene torch for cutting, then you know what I mean.  Adding extra air results in a hotter flame.  This might be good if you are trying to cut through metal with a torch, but it is NOT good in an engine because you can literally cut a hole through your piston with too lean of a mixture. 

So, how do you add extra fuel on a turbocharged engine?  There are some different ways.  Let's assume we are dealing with a fuel injected engine, which is most common these days.  Here are some ways you can increase fuel flow:

1) ADJUSTABLE FUEL PRESSURE REGULATOR - You can install a boost referenced adjustable fuel pressure regulator, which increases fuel pressure as boost pressure increases.  An adjustable fuel pressure regulator will allow you to adjust the base fuel pressure.  Then the boost reference will change the fuel pressure from that baseline point.  As you might imagine, increasing the pressure through a spray nozzle (injector) will increase the amount of fuel flowing through that nozzle.  This is true IF AND ONLY IF your fuel pump is capable of providing the additional flow at the higher pressure.  Pumps are designed to flow a certain amount at any given pressure.  So turning up the pressure, can actually result in lower flow if the pump can not handle it.  On my Merkur XR4Ti, I installed a much bigger Walbro 255gph fuel pump in the tank, since I planned to be running more boost than stock and also flowing much more air (and fuel) through the engine.  Changing fuel pressure is one way to try to add fuel to match the additional airflow provided by a turbocharger.

2) BIGGER FUEL INJECTORS - You can also install larger fuel injectors that will flow more fuel for any given fuel pressure.  In theory, you could just figure the additional amount of air flow under boost and then install larger injectors to match that.  Problem with this idea is that off boost the engine will be running too rich with the larger injectors.  As a side note, fuel injectors are usually rated by the amount of fuel that they can deliver in a certain amount of time at a standard pressure.  A common unit for rating fuel injectors is pounds per hour (pph).  I know that pounds per hour seems a bit odd when dealing with a liquid, but if you want to convert this to something a little more intuitive, you can just take the pph rating and divide by 6 to get a pretty good calculation of the gallons per hour rating of the injector.  For example, let's say you have 42pph injectors, then that would be around 7gph.  While we are discussing fuel injector ratings, let's touch upon another important specification for fuel injectors, and that is injector impedance.  There are high impedance and low impedance injectors.  In terms of high vs low impedance injectors, it is true that low impedance injectors are better from a performance tuning standpoint, because they can be run at near 100% duty cycle reliably.  On the other hand, high impedance injectors can not be pushed to these limits without causing erratic performance and possible damage to the injector from overheating.  Regardless of what you have, it is very important that you don't mix up different impedance injectors.  In other words, if your car originally came with low impedance injectors, then that means that the computer in your car has injector drivers that are matched to low impedance.  You need to make sure any other injectors that you install are also low impedance.  Let's take for example the Ford 2.3 turbocharged engine.  It came from the factory with 35pph low impedance Bosch injectors.  I upgraded my injectors to a set of low impedance Bosch style 45pph injectors from RC Engineering.

  Fuel Injectors

With the computer being calibrated for 35pph injectors on my Merkur, you would expect that running with injectors that are nearly 30% "larger" (not physical size, but flow rate), that the engine would run too rich when off boost.   Interestingly, the engine ran quite well on the larger injectors, even though the car's computer was calibrated for the smaller 35pph injectors.  I had an air/fuel ratio meter and the engine did not run excessively rich when off boost.  I think the reason for this is that the O2 sensor is constantly adjusting the injector pulse width (duty cycle - amount of time injector is on & spraying).  So, the computer was probably compensating for the larger injectors by dialing back the injector's on time.  Even though the engine ran OK, it was not optimal.  The proper way to install larger injectors is to re-calibrate your fuel curves in your engine management computer.  And that brings us to the next topic of discussion. 

3) RE-PROGRAMMED ENGINE MANAGEMENT - "Performance chip", "tuner", "programmable engine management", or whatever else you might like to call it.  Basically, you want a way to adjust the factory engine management to accommodate the modifications that you made.  Obviously, if you drastically increase the power output of your engine over the stock ratings, then your car's stock computer calibration will not work well any more.  In my case, I had nearly doubled the power output of the stock engine on my Merkur XR4Ti, and so the factory programming was no longer a good match for my modified engine.  My tuner allowed me to make adjustments using a laptop.  Since the software was relatively simple, I was able to use an old, outdated laptop and it worked fine.  The only problem that I had was the laptop battery would not hold a charge, and so I just kept the laptop plugged into a small power inverter that converted 12VDC from the cigarette lighter  to 120VAC.  If you really want to get your tuning done as quickly as possible, then you probably should find a reputable tuning shop that has a good chassis dyno.  They can set up your car on the dyno and monitor the air/fuel ratio and get your fuel curves dialed in to match your setup.  Personally, I was always on a limited budget and I am the type of person that likes to do things myself, so I just did a lot of trial an error to get my engine tuned.  I used a lot of "seat of the pants" tuning and I also used my gtech meter to measure changes in power output.  In addition, I had an air/fuel ratio meter installed in the cockpit, so I could roughly keep an eye on what the Air/Fuel (A/F) ratio was doing.  I did not have the much more precise wide band air/fuel ratio monitoring system, but even so my simple A/F meter would tell me if I was way off in my tuning.  It is recommended to get a wideband O2 sensor so that you can more closely monitor your fuel delivery.  Some people also prefer to have an Exhaust Gas Temperature (EGT) system installed on their vehicle.  Then the fuel delivery can be tuned to ensure that the EGT does not get too high.  Too lean of mixture can lead to greatly increased exhaust gas temperatures.  If the A/F gets too lean, then temperatures can rise to the point that your turbine wheel will be damaged.  In addition, a lean mixture can blow torch a hole in a piston, or lead to destructive detonation that can destroy your engine.  So, before you add a turbocharger or upgrade an existing turbo, be sure that you have a way to monitor your air/fuel ratio either with a direct reading from an O2 sensor or an indirect reading of the EGT.  

LOOK BEFORE YOU LEAP - Really, before you can effectively turbocharge any engine, you need to have a way to monitor your air/fuel mixture before you add a turbocharger.  In other words, you can't just slap on a turbocharger and expect that things will go well.  They will not.  That's why I used the phrase "look before you leap".  You can't just jump into turbocharging haphazardly or else your engine will very likely be ruined in short order.  Not only that, but your engine will likely not run properly anyway.  Remember, just adding more air with a turbocharger does not increase power in itself.  The additional air is only useful if you have additional fuel to match it.  And just carelessly adding fuel doesn't guarantee success either.  Too much fuel and your air/fuel mixture will be too rich and it will kill performance.  Too little fuel and your A/F ratio will be too lean and you can destroy your engine.  That's why it's critical that you have a plan up front of how you will monitor your air/fuel ratio while tuning your turbocharged engine.  Below are a couple examples of the type of narrow band air/fuel meters that I've used on different turbocharged vehicles I've owned.  These A/F meters tap into the existing narrow band O2 sensor that already exists on almost all fuel injected vehicles.  They are inexpensive and simple to hook up.  They are not as accurate and precise as wideband air/fuel gauges.

Autometer A/F Meter

Intellitronix and Auto Meter Narrowband Air/Fuel Gauges

Wideband air/fuel gauges are much better for fine tuning the mixture on a turbocharged engine.  They are also more expensive and more difficult to install.  Expect to pay 3-4x as much as a narrowband air/fuel meter.  Part of that cost is the wideband O2 sensor itself.  You will need to have the new wideband O2 sensor welded into your exhaust system.  This involves cutting a hole in the exhaust pipe, welding in a threaded bung, and then screwing in the new sensor.  Not complicated if you are experienced with welding.  If you are not, then you will need to take your car to a exhaust shop that can do it for you.  This can further adds to the costs of a wideband system.  Even so, I would say that this is a good investment in the longevity of your engine, and also a useful tool for extracting maximum power.

Wideband Air-Fuel Gauge

Wideband Air/Fuel Meter

If you really want to be cautious and closely monitor your turbocharged engine, then you can also get a Exhaust Gas Temperature (EGT) gauge as well.  An EGT gauge (also referred to as a pyrometer) requires that a thermocouple be installed into the exhaust system (preferably before the turbo) in order to monitor exhaust gas temperature.  This can be useful information because too lean of a mixture can lead to too high of exhaust temperature that can lead to engine damage.  If your EGTs get high enough, you can actually melt the blades on the turbine wheel.  At the very least, this would destroy your turbocharger.  How high is too high?  Generally, if you keep the temperature at the turbocharger inlet below 1300F, then this is still considered safe.  Above that temperature, and there are much greater risks for turbocharger damage.  Keep in mind that 1300F is considered a limit at the turbocharger inlet.  That means you need to install the thermocouple prior to the turbocharger.  This often means that you will need to drill and tap a hole in the exhaust manifold.   On some turbocharged engines, there can be some exhaust pipe leading into the inlet of the turbocharger.  This is more likely found on V engines (like a V8) where the exhaust gases from each bank of cylinders is routed with exhaust pipe into a Y type junction at the inlet of the turbocharger.  This is how my Ford E350 with 7.3L turbodiesel engine is configured.  In this type of situation, you can drill a small hole in the exhaust pipe for the thermocouple and then use an integral worm clamp to secure the thermocouple in place.  This is much easier than trying to drill and tap a cast iron exhaust manifold.  Just remember, it's much safer to monitor the EGT prior to the turbocharger.  If you install the EGT probe after the turbocharger in the exhaust pipe that exits the turbo, then you will get much less reliable temperature readings.  The temperature after the turbo will likely be 100's of degrees different (lower) than at the inlet of the turbo.  This is because some of the thermal energy of the exhaust gases go to spin the turbine wheel.  This in turns results in a lower temperature of the gases as they exit the turbocharger, and this reduction in temperature an vary depending on things like engine load.  That's why it's considered best to read the temperature of the gases prior to them entering the turbocharger. 

EGT Gauge 

HOW SHOULD I DO IT? - This is a big question.  If you happen to own a popular vehicle like a Honda, then it's very possible that complete turbocharging kits are available for your engine.  If money is not a limit, then you might want to consider a complete kit like this.  If you do go this route, then all of the R&D has been done for you already.  All you need to do is follow the directions and install the kit.  It's still a lot of work, but this is a much easier and safer way to go.  It can also be very expensive.  Another possibility is if you own a vehicle that has a sister model that was turbocharged.  You can sometimes swap over the turbo system and necessary support systems (like fuel and computer systems).  Probably easier in some ways is just to swap over the entire engine rather than just swap over pieces of the turbo system.  In my opinion, if you are going to go to all this trouble, then you might as well just consider selling your existing car and buying a car that comes from the factory already turbocharged.  Another way to do turbocharging is to do a custom installation where you design and install the system from the ground up.  It takes much more time and effort to do it this way.  This is not something to be taken lightly by a newcomer to the world of turbochargers.  Doing it all from the ground up carries with it much higher risks of surprises, problems, and potential engine damage.   Even so, it can be very rewarding to have a one-of-a-kind custom turbocharger installation.  One final bit of parting advice, as touched upon earlier, if you are just getting into turbocharging, then you might consider starting off with a factory turbo vehicle and go from there.  You can learn a tremendous amount by working on and modifying a factory turbocharged vehicle.  Once you gain some more practical experience, then you will be better prepared to consider and venture off doing your own custom turbocharger installation. 

 

 

 

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