Turbo Basics 101

[*sic 1]

here are some basics i have come across that seem pretty good to begin your understanding of what Forced Induction involves

(please note - This has Honda application through it, but the general info is the same thanks)

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The advent of improved international standardized manufacturing techniques and standards has led most folks to come to the realization that cars are made a lot better than they were ten years ago. Simply put, improved mechanical tolerances and increased reliability have greatly increased. If anything, that should encourage you to coax a little (or a lot) more power out of your car.

A lot of folks go down the path of traditional powertrain modification. They do your average "breather mods" (intakes, headers, exhaust), play with fuel maps, modify ignition timing. Those with more time, know-how, and money on their hands resort to headwork -- porting, polishing, cams, etc. However, it's the dream of many an automotive tuner to seek power through forced induction (turbocharging, for one) and creating more power from less displacement, which, essentially, is what turbocharging is. For most people, there are some VERY expensive aftermarket turbo kits out there. Those with money will trust experts to install such a setup. For those who don't have so much money but KNOW WHAT THEY ARE DOING, there are turbo setups that cost in the hundreds of dollars rather than in the thousands. This article is just to give you insight on some of the possibilities that exist. IF YOU DON'T KNOW WHAT YOU ARE DOING, don't proceed! Turbocharging your engine improperly is a VERY easy way to cause thousands of dollars in damages, not to mention serious risk of damage to one's self. If you do something dumb, we at Bimmersport.co.nz take NO RESPONSIBILITY.

For the laymen who can't distinguish a camshaft from a halfshaft, here's turbocharger theory 101 in a nutshell. Engines are designed to work like a pump. Air and fuel are mixed together, and then ignited. The explosion provides power. Air and fuel must be combined in a specific ratio -- 14.5 of air to one part of fuel. If there is too much fuel in relation to air, the engine runs in a state of "richness". This leads to poor performance and lower fuel economy. An excess of air in relation to fuel will cause the engine to run in a state of "leanness". This leads to bad bad things -- detonation (explosions happening before they should, when the engine is in a poor position to receive the benefits of it), and high combustion temperatures (which, if hot enough, WILL melt parts of your engine). The point is to maintain that magical "stoichiometric" ratio of about 14.5 to 1. Ok. Pay attention -- this part is where power comes in. The more of this 14.5-to-1 air/fuel mixture you can force into your engine and ignite, the more power it will make. A turbo charger is essentially a double-sided pinwheel. The rapidly flowing exhaust gases spin the exhaust side (the hot side). This is connected via a turbine shaft to the compressor side (the cold side), which spins up in the range of tens of thousands of RPM. This action pressurizes the air intake charge -- thereby forcing more air into the engine. Now, if you've been following along this whole time, you should be asking yourself, "won't all this extra air cause the engine to run in a state of leaness?" That's correct! Specially designed fuel injection setups provide the extra fuel your engine needs.

At this point, you reach the two most important questions involved with turbocharging. 1) How do I get a turbo attached to my car and 2) how do I provide enough extra fuel in the right amounts at the right time to accommodate this influx of air?

The easy way.

If there is a turbocharged version of your engine on the market, you'll have an easier time finding parts and doing the installations. This makes things MUCH easier and cheaper, seeing as a) chances are, your car's manufacturer has designed proper clearances and tolerances into your car to accept turbocharging and these parts are quite plentiful and cheap at your local junkyard! This includes (but isn't necessarily limited to) 3rd and 4th generation Toyota Supra, all generations of the Nissan 300zx, 1st and 3rd generation of the Nissan 200sx, 2nd generation Toyota MR2, 91-99 Mitsubishi 3000GT. In part four of this series, we'll do our best to post a more complete list -- including the myriad of turbo Saabs, Volvo's, and Porsches out there. The parts you'll need from your car's turbo big brother will include the turbo, oil lines, turbo manifold, intercooler, compressor bypass valve (more commonly known as the blow-off-valve), downpipe, ECU, injectors, fuel pressure regulator, fuel pump, air flow meter, and as much as the intake/intercooler piping as possible. Here's a breakdown of what each part does.

The Turbo

It's the power adder, silly. When picking one up from the junkyard, make sure the turbine wheel spins freely. Also, make sure the wheel has no play. It should spin--period. It shouldn't wobble, it should wiggle, it shouldn't move in and out. The average price of a used turbo is in the $100-$200 range. Try to get the factory oil lines that go to and from the turbo. You will need to tap the sender line into the block someplace, and the return line into the oilpan to ensure a flow of oil through the turbo.

Turbo Exhaust Manifold

This replaces your stock exhaust manifold. Rather than guiding spent exhaust gases straight into your downpipe and out of your tailpipe, the turbo manifold directs the exhaust gases into your turbo to spin it. If one isn’t in existence for your vehicle, it can be manufactured for anywhere in the $400-$800 range.

Turbo Downpipe

Chances are, your factory non-turbo downpipe will not mate up properly with the turbo exhaust outlet. If the turbo downpipe is unavailable for your car, your local muffler shop can fabricate one for about $150. An aftermarket unit will cost upwards of $200.

Make sure you get the downpipe to mate with your exhaust system.

Intercooler

Much like a radiator for the incoming air charge, the intercooler cools the intake air charge to temperatures closer to ambient, condensing it and allowing you to fit more into each combustion stroke. This also helps in reducing combustion temperatures (bad) and helping prevent against detonation (also bad). Stock units from the junkyard can usually be had for between $25-$75.

Compressor Bypass Valve (CBV) or Blow Off Valve (BOV).

This is what usually makes that pffffsssshtt sound on turbocharged cars. This valve does more than make that funny noise and add that wank factor to your ride, however. Its main purpose is to relieve the pressure on the intake air charge between shifts. When you shift, you usually let off the gas pedal. That in turn slams the throttle plate shut. Your pressurized intake charge now has no where to go. What the CBV does is vent this pressurized air -- either back into the metered intake stream in the plumbing before the turbo, or out into the atmosphere. If this air is not vented, it will send a pressure wave back down to the turbo, trying to reverse the direction that the turbo is spinning. This is not good for turbine longevity. Decent OEM CBV’s will usually retail for about $30-$50. There are benefits of going with aftermarket units like the Greddy Type S, which is adjustable

ECU/Injectors/Fuel Pressure Regulator/Fuel Pump

This is primarily, the fuel system from the turbo version of your car. Chances are, the turbo version of your car will have larger higher capacity fuel injectors and have a different air metering system than your normally aspirated car. This system, when functioning properly, will inject the proper amounts of fuel, proportionate with the incoming air, at proper intervals and duration. Several sensors (air flow meter being the major one) detect the volume, temperature, (and in some cases, velocity) of the intake air charge. This information is sent to the ECU, or computer, which in turn computes how much fuel is required to mix with this air. Once this is calculated, the ECU fires the injectors. The fuel pump and fuel pressure regulator are in place to see to the fuel demands of the injectors.

Oil/Coolant Lines

These are very important systems and should not be ignored. Simply put, to remain lubricated and within operating temperatures, a turbocharger needs a constant supply of oil and coolant flowing THROUGH it. Your stock cooling system can usually be teed off with radiator hose and redirected through the turbo to supply coolant. Oil on the other hand will require a certain grade of hose that withstands much higher temperatures. Fittings will need to be created both in your oilpan for the oil drainage line from the turbo and in a source of fresh oil somewhere before the turbo. The easiest solution for that (since most engines require tapping to get a live oil feed) is to install a remote oil filter relocation kit. These attach where your oil filter normally is, re-route the oil to a remotely mounted oil filter, and provides a return line back to the block for the filtered oil. This is the perfect place to tee off the connection and run a line to supply oil to your turbo. Your average kit will run you about $100.

Intake/Intercooler Piping

This is what holds everything together. This piping, held together by friction fit, hose joints, and clamps, will allow air to flow through the air filter to the turbo, from the turbo to the intercooler, and finally from the intercooler to the throttle. Stock factory pieces are usually made of plastic, but tend to fit fairly well. Pieces that you're missing can usually be made from large radiator hoses or pieces of generic muffler piping of varying lengths and bends. If you're feeling extravagant and want a better flowing system, we recommend taking this task to your local muffler shop. You should see to it that beads are welded into the piping where clamps will be used to ensure a fit that will not come apart should you start running large amounts of boost. Follow this up with some powder coating or anodizing, and you've got a pretty trick looking setup.

Gauges/Monitoring Equipment

Ideally there are three different gauges you should have when you embark upon this project. First and foremost is an aftermarket boost gauge. Decent units are made by Autometer for about $40. Best thing is, these units read in ENGLISH, that is, in PSI. These gauges will tell you what kind of negative and more importantly, positive manifold pressure your turbo is creating. Next is an air/fuel ratio gauge that will tell you how far you are from having a stoichiometric mixture by reading the signal coming from your O2 sensor.. Intellitronix makes a 52mm unit that fits into your average a-pillar gauge pod for about $30. Finally there is the EGT (exhaust gas temperature) gauge. When an engine is in good running order, it should be at about 1450 degrees Fahrenheit. Temperatures below that will indicate a state of richness, and temperatures above that will indicate a state of leanness (BAD). An EGT gauge is essentially a voltmeter that displays the output from a thermocouple, or pyrometer, that sits in the exhaust stream and converts heat to an electric signal. A full complement of these gauges, coupled with some good common sense, we go a long ways in keeping you from turning your motor into a metal foundry.

What we've gone over are some basics of a turbo conversion.

Turbo Lag and Throttle Response

At any bench racing jam session, you're bound to hear vigorous, heated discussions in the all-motor crowd about turbo lag and poor throttle response on turbo cars. Actually, many people confuse "turbo lag" with "boost threshold". Boost threshold is the lowest RPM at which a turbo will generate positive manifold pressure at maximum engine load. Throttle response is not affected by adding a turbo on to a non-turbo engine, though it may feel that way as you're waiting for boost. In actuality, your engine is making at least as much power as it was before the turbo, except now you're waiting for the rush of boost-induced torque.

And while we're on the subject of boost, "boost" is manifold pressure above atmospheric, and is typically measured in pounds per square inch (psi) kilo Pascals (kPa), or bars.

Engineering Basics

In Part 1, we outlined the parts needed to convert your non-turbo daily driver into a high-powered turbocharged beast. The same concepts behind factory turbo cars can be directly applied to non-turbo vehicles as well, except that availability of things like factory turbo exhaust manifolds may be little more than a nice dream. But that's ok - we've learned from many a Honda owner that fabricated turbo exhaust manifolds and plumbing are relatively common and inexpensive. Another important factor to consider is that most aftermarket exhaust manifolds come with "special features", such as stainless steel construction and tuned-length runners.

If you're considering a turbo upgrade to your non-turbo vehicle, you may be wondering how much added "stress" the engine can take from the added power of the turbo. Undoubtedly, you've heard horror stories about retrofitted turbo engines blowing due to the failure of a connecting rod. Let's examine the stresses put on engines during a normal combustion cycle, specifically the connecting rod.

There are two main types of force applied to automotive connecting rods; power load (compressive) and intertial load (tensile, or pulling). Expansion of the burning air/fuel mixture pushes the piston down, and in turn the connecting rod acts as a pillar, pushing the crankshaft to turn up-and-down power into round-and-round power.

It may seem that connecting rods are miraculous devices, being that at peak cylinder pressure, even the weakest running engines can put over 6,000 lbs of compressive force over a single connecting rod on the power stroke! But when we look at the forces exerted on the connecting rod as it yanks the piston away from top dead center, that is when real eye-opening forces may be observed. Doubling the engine RPM quadruples intertial loads on the connecting rods!

Conversely, doubling engine output does not double the compressive force on the connecting rod. Engine output is a function of the average cylinder pressure during the piston's travel down the cylinder bore, with peak pressure being a relatively small part of the equation. With double the air/fuel mixture in the combustion chamber, peak cylinder pressures are increased only about 20 percent. Overall, compressive loads on connecting rods are greater than tensile loads, but it is a lot easier to double a tensile load than it is to double a compressive load. Additionally, compressive loads do not fatigue metal as tensile loads do, since compressive loads squeeze the molecules of metal together in the connecting rod, while tensile loads attempt to pull them apart.

So, "Why", do you ask, "are connecting rods the weak link with an aftermarket turbo?" This is because the "stress" a connecting rod endures is the difference between the compressive and tensile forces applied to it. The greater the difference, the greater the likelihood of connecting rod failure. Increasing engine output increases the stress on the connecting rods because higher engine output is attained although the engine is run in the same RPM range it was when there was no turbo. As a general rule, maximum engine output can be increased by approximately 50 percent before compression loads reach a point of connecting rod failure

Nomenclature

Any armchair hotrodder has undoubtedly seen turbo naming conventions such as T25, T3/T4, Super 60, 16G, 18G, and 20G. These are part numbers assigned to turbos of specific sizes by their respective manufacturers; in this case, the first three turbos are manufactured by Garrett, the last three, manufactured by Mitsubishi. Each turbo has its place in the automotive world, and the one you choose will depend largely on the desired end result as well as how easy it can be installed on your application. For instance, if you're upgrading the turbo on your Mitsubishi Eclipse, then a smart move would be to take a look at other Mitsubishi turbos since these units can be easily installed on Mitsubishi cars. And as far as Brand X performance versus Brand Y performance, we find that selecting a brand of turbo is like selecting a brand of toilet bowl cleaner: they all get the job done no matter who's name is on the label.

You may also be familiar with terms such as A/R or compressor trim. A/R is short for "Area/Radius" and is a number that is derived by the area of the compressor nozzle divided by the distance of the nozzle center from the compressor center. A/R is a way we allow the scientists to fine-tune air delivery and boost threshold properties of turbos within a size range so that we can have very fast cars without reading many tomes containing tragic quantities of mathematical formulae. Since we are not all fluid dynamicists, a little bit of telephone research is all that's needed to select the correct turbo for your application.

System Design

The first thing to consider while drawing out your system on paper is how much money you're willing to spend. Some people are on a tight budget, some just want to make as much horsepower as possible on, say, common pump fuels.

Then, you'll need to draw up a list of components needed. Generally speaking, you'll need the turbo, a suitable exhaust manifold (or a modified stock manifold on non-turbo cars), piping to carry air from the turbo to the throttle body, modification to the existing exhaust system so it bolts up to the turbine housing, a wastegate, and a method of increasing fuel delivery while on boost. Of course, this list of components may change for the "odd" turbo setup, but in most cases, this is what's needed for late-model fuel injected automobiles.

Then there are the optional pieces such as the intercooler and blowoff valve.

Let us embark on a journey of designing a hypothetical DIY turbo system. For simplicity, we'll use the late-model Honda Civic as an example. Limitations of the stock 1.6L SOHC engine are well documented, and our hypothetical system will be designed to extract as much power as safely possible from the engine for street use. A little bit of telephone research indicates that a Garrett T25 turbo should do the job, having a compressor trim of 55 and a turbine housing A/R of 0.49. A larger turbo "could" be used, with the promise of more power, but running 8 psi of intercooled boost should put engine output at around 170 hp with an intercooler. 170 hp is the upper safe limit of power this engine can produce on pump fuels. We'll also factor in a blowoff valve and intercooler to the system for maximum show 'n go.

Exhaust Manifold

If you own a non-turbo vehicle that has a turbocharged counterpart, such as the Nissan 300ZX, Toyota Supra, or Nissan 200SX, you are in luck. An exhaust manifold that will support a turbo is just a short trip to your local salvage yard or dealership. For other vehicles, such as Honda/Acura, aftermarket turbo exhaust manifolds can be obtained just as easily. Those of you who own the "odd" vehicles, such as the AE92 Toyota Corolla, may have some difficulty finding an inexpensive exhaust manifold that is turbo-capable. In cases like these, you can either get a 100-percent custom manifold fabricated, or modify the existing stock manifold by adding a flange that will accept a turbo. In the case of the Civic, turbo manifolds are available from several sources including DRAG and GReddy.

Turbocharger

As indicated earlier, the hypothetical system will use a Garrett T25 turbo. Commonly used in mid 1980's small caliber performance cars, the T25 is plentiful and inexpensive. Of course, since most salvage yard turbos look like the one in the photo, it's a good idea to spend the $150 for rebuild service. DIY rebuild kits can be had for around $50, and should include a complete set of bearings, seals, o-rings, and gaskets.

Wastegate

Most turbos for street use will have an integrated wastegate, an internal wastegate. This is the simplest wastegate to use, from an installation standpoint, since it is already attached to the turbo and requires a minimum of vacuum hoses to work. The drawback of the internal wastegate is that on occassion, it will not flow enough exhaust gas for "perfect" boost control. Higher-flow wastegates are available, the external wastegate. These allow for more precise boost control as well as flow capabilities for very high powered engines, with a drawback of more moving parts and more complex vacuum configuration. The Cosworth engine in the photo uses an external wastegate, which relieves pressure in the exhaust manifold so that exhaust gases do not flow through the turbocharger's turbine, and thus, limits boost.

Adding Fuel

Several modifications will have to be made to most factory fuel systems when you convert over to boosted power. A proportional amount of fuel must be added with the additional airflow a turbo provides, and there is more than one way to skin a cat. The most widely accepted solution is using a boost-indexed fuel pressure regulator. This device works by drastically increasing fuel pressure to the injectors according to how much turbo boost exists in the intake manifold. Typically, 12 psi of fuel pressure is added for every 1 psi of turbo boost. The limitation of this device comes around perhaps 10 psi of turbo boost, when you're adding over 120 psi to the fuel system pressure. Fuel pressures such as these can actually "clamp" injector pintles shut, causing obvious problems with air/fuel ratio management.

The DRAG turbo system on this 1999 Civic Si uses a boost-indexed fuel pressure regulator and runs mid-12's in the quarter mile.

Other methods of fuel management exist, such as adding additional injectors. This allows an electronic solution to fuel management on boost, which is potentially more precise than mechanical methods and allows for any boost level to be run. (Assuming, of course, your engine and turbo is up to the task of providing "any" boost level.) The photo depicts a 2JZGTE Supra with six additional 550 cc fuel injectors controlled by an HKS Additional Injector Controller.

Most of the "other" methods one may encounter are nothing more than band aid solutions to adding fuel. A common trick is to use a boost pressure switch that alters the coolant temperature sensor output once positive manifold pressure is reached. Since fuel pressure isn't really altered while on boost, remember that an engine spinning twice as fast has half the time for injectors to deliver fuel. Additionally, since the amount of fuel added to the engine is so imprecise, it's likely that the air/fuel ratio will be drastically rich at low RPM, and drastically lean at high RPM.

For higher boost levels (over 5 psi typical), stock fuel pumps cannot provide the volume or pressure required for on-boost fueling. In-tank, high-flow fuel pumps are available for most late-model vehicles, but some people prefer even higher flowing external fuel pumps. Bosch and Accel make relatively inexpensive external fuel pumps that can flow enough fuel to support over 400 horsepower!

Blowoff Valve

An object in motion tends to stay in motion. That's the key principle behind having a blowoff valve in your turbo system. While not exactly necessary for a turbo system to work, a blowoff valve will help turbo boost response between shifts. For very high-powered vehicles, one blowoff valve may not be enough to vent excessive boost when the throttle is closed; in this case, it's perfectly acceptable to use several blowoff valves.

Intercooler

An intercooler is simply a heat exchanger. It takes heat gained by the compression of air and "exchanges" it out to either the atmosphere or an on-board water resevoir. It's easy to see how compressed air exiting the turbo goes through a huge "radiator", and then into the engine throttle body.

Since a good intercooler can very well be the single component that breaks the bank, we go back to the salvage yard. Many factory turbocharged vehicles (Volvo, SAAB) have large air-to-air intercoolers that can be had for a song. The intercooler pictured here came from a wrecked Mitsubishi Starion and was purchased for $40.

Tech Tricks

Since air/fuel ratios can be difficult to fine tune on some aftermarket turbo systems, simple electronic means are a perfectly viable method of roping in fuel control. Simple fuel computers such as the Field SFC or A'PEXi Super AFC can help restore losses in driveability or fuel economy when mechanical fuel control methods are used.

Edited November 11, 2003 by *sic

[Guest Spargo]

I highy recommend we all read this to stop the spread of mis-information in BimmerSport

I also recommend you read Turbo Basics by Corky Bell, and 21st Century Performance by Julian Bell. These boys know what their talking about, SOME OF YOU DO NOT!

Oh, and read the Art of War, by Sun Tzu (sorry, that just slipped in)

[Guest Andrew]

Stoichiometric is 14.7:1 ..

Otherwise its not a bad writeup .. for people who aren't sure which wheels are the back ones

[Guest Andrew]

I also recommend you read Turbo Basics by Corky Bell, and 21st Century Performance by Julian Bell. These boys know what their talking about, SOME OF YOU DO NOT!

*cough* pod filter gives horsepower.. *cough*.. heh couldn't resist

[Gus 5]

niiice...just had time to read properly...very informative and helped clear up some misunderstandings..cheers! now...got one about supercharging???

[sidewayswhat! 0]

Awesome thanks, will be refuring back to this when I turbo my M50B25

[hybrid 1043]

and from the warp in time ... a thread from nearly 10 years on is reborn ...

[m325i 709]

What ever happened to *sic? - he used to troll heaps...

[Silver Fox 43]

We all grow up sometime, oops, did I say that?

[DrphTa 5]

Epic thread dig hahaha