What the hell is tuning

[Indecisive]

[span style=\'color:red\']Posted by Arro[/span]

Many of you have some familiarity with this term, but perhaps there still exists some enigma behind it for many people. This post is a bit long so bear with it.

Considering this verb is used often to decribe alteration of a musical instrument, your car shouldn\'t be too different in definition.

[url]http://www.dictionary.com[/a] lists this for \"tuning\" in def. #4:

4. To adjust (an engine, for example) for maximum usability or performance.

In the early days of automobile performance this centered around a carbeurated environment, with no computers and mostly just mechanical and pnumatic (air/vacuum) control over flaps and actuators. Carb jets were changed out, additives like toulene were mixed with gasoline, heads were ported, and compression ratios increased. To a varying degree this was the extent of tuning activity in the carbeurated days.

Today, the concept of \"tuning\" is more more complex, involving port geometry, octane ratings, positive pressure, a whole slew of computer-monitored sensors watching various operations, fuel injection options, electric fuel pumps and fuel pressure increases, timing advance, variable valving, compressor efficiency (forced induction applications), extra injection, even the casting geometry of things like intake manifolds and exhaust systems.

However, to a greater degree, it\'s still the process of adjusting the engine, suspension, or transmission, \"for maximum usability or performance\".

Since it is generally accepted that one cannot get maximum perfomance without altering and testing components, experimentation and safety become cheif elements of tuning. Good tuners have as much common sense about safety as they they have ambition to squeeze out maximum performance.

In many a modern car interest, the aim is to make the most power possible out of small-displacement 4 and 6 cyllinder engines, since these are the most abundant, and manufacturers have offered them in more and more amazing options.


THE BASICS:

In the naturally-aspirated end of things, these cars generally have close-tolerance valving (sometimes even trick valving like VTEC or Toyota\'s VVTL). Light weight cars, with small displacement engines using high-octane fuels, advanced timing technology, closer tolerances, and computer control allow these little wonders to pack a punch. Generally from the factory the engine componentry is scientifically-derived, however there always exists room for improvement in design, and so better performing components are swapped out to push the engine and find its limits. The manufacturer typically sets \"limits\" that are way below the engine design capability, in order to ensure both safety as well as reliability for mass-production. By safely going beyond the manufacturer-configuered output, you can increase your potential power and push the engine to its *actual* limits. You can even increase its limits.


TURBOCHARGING:

In the turbocharged and supercharged world, many of these engines take well to forced induction, and the computer control along with copmputerized and high-tech aftermarket componentry allow for high boost in a reliable engine. Injenuity from tinkering sessions also revamps factory methods and OEM equipment, producing improved results. We have learned over the past three decades of automobile performance that positive pressure requires more and more precise fuel mixture and more accurate monitoring, along with a number of lesser yet still important areas of operation. The higher the positive pressure, the more precise the mixture must be, and the margin for error gets smaller and smaller. The consequences of mistake also increase as the amount of forced air increases in an engine.

This is much more serious than merely increasing cyllinder compression with a change of pistons. The dynamic \"compression\" in a cyllinder under *high* boost is (at its maximum boost moment) far above the static compression in high-ratio naturally aspirated engines. Because of this, all the engine components take a beating. Manufacturers often maintain reliability by building turbocharged and supercharged engines with stronger internals than their naturally-aspirated counterparts. Another technique manufacturers often use is lower compression pistons, which translates to less constant stress on the engine at idle and cruise speeds (engine only sees high stress during boost operations).

[Indecisive]

In order to reliably run an engine under boost (or at higher than stock levels for OEM turbocharged cars), fuel and air temps must be perfectly balanced or nearly so to prevent major engine damage. \"Tuning\" might begin with bolt-on parts, but as you turn up the boost, tuning encompases fuel mixtures, knock monitoring, timing, and air temps.

First and foremost is fuel mixture. in most modern turbocharged vehicles, the computer monitors fuel mixture via O2 readings from the \"oxygen sensor\" (also called an O2 sensor).

OXYGEN SENSOR
Also called an \"O2\" sensor. Device that monitors oxygen content in engine exhaust to correct air-fuel ratio. These can be one, two, or three-wire sensors. They are usually mounted in the exhaust manifold or the downpipe. Many turbocharged vehicles mount the O2 sensor in an \"O2 housing\" that sits between the turbocharger\'s exhaust outlet and the downpipe. On the S12, CA18ET-equipped cars have the O2 sensor on the O2 housing. For CA20E-equipped cars, it is in the exhaust manifold.


COMPUTER CONTOL:

In most turbocharged cars, the computer uses this sensor, along with air temp sensors and either an airflow meter or a \"manifold absolute presure\" sensor (MAP for short) to monitor the engine. The O2 sensor tells it how the fuel mixture is, and under \"closed loop\" operations, the fuel mixture is constantly changing, based on inputs from the above sensors. Closed loop is generally used for idle and cruise operations, however, and much of performance automotive deals in \"wide open throttle\" (WOT) or nearabouts (meaning high reving driving).

Since inputs are sometimes slow to respond (O2 signals for example), often times the car\'s computer has a second mode of operation known as \"open loop\", where the fuel system is controlled using preset values in the computer to operate the engine. A typical turbocar computer will enter this state as a result of a WOT condition or a value close to it. This is determined usually by throttle position (using a throttle position sensor attached to the throttle body plate). In this state, there is little if anything the computer can do to adjust the fuel settings to match changes in maximum boost peak. The result is what is called an \"overboost\" condition, where the positive pressure from the turbocharger exceeds the factory-tuned limitations of the engine and supporting fuel system. Some vehicles have countermeasures to prevent this.


OVERBOOST PROTECTION:

In some cars, the computer has a shutdown feature that kills most or all power to the engine when overboost is reached. Other cars employ methods to prevent overboost from ever occuring, using relief valves.

A \"pop-up\" valve is a safety device on the intake manifold of a CA18ET (turbo) S12 that leaks boost when PSI exceeds factory-tuned limits. A spring-loaded door opens (as boost defeats the spring\'s PSI rating) when you go above the factory boost. This prevents an \"overboost\" condition and protects the engine from damage.

If you want to go over the factory boost level, the first thing you must do is permenantly seal this valve. This effectively defeats the overboost safety feature in an S12. This also means that you are now able to force more air than the stock fuel system can support, and risk damaging your engine.


I\'VE DEFEATED MY OVERBOOST COUNTERMEASURES. NOW WHAT?

Once overboost countermeasures are defeated, you are left with the challenge of delivering the proper amount of fuel and air for your desired boost level. This is achieved in a variety of ways, such as using larger injectors, adding extra injectors into the air intake path, increasing fuel pressure (by means of a larger electric pump and/or an adjustable fuel pressure regulator), increasing octane rating of your fuel, and using a variety of add-on computer components to alter the injector operations (injector pulse-width settings).

While doing this, the air temps must be taken into consideration, since the hotter the air temps get, the more tendency there is for \"detonation\" to occur.


AIR TEMPS, FUEL, AND DETONATION:

Detonation, also known as \"preignition\", is the explosive, uneven burning of fuel, causing engine knock (engine noise caused by detonation). In a turbocharged vehicle, this is critical, because the extra added air must be precisely balanced with the proper amount of fuel to cool it, or the friction generated by compressing the air will create too much heat, igniting the fuel prematurely, and resulting in potentially severe damage to the piston, valves, cyllinder wall, head gasket, and an assortment of other components.


TURBOCHARGER EFFICIENCY:

Sufficient fuel will cool the air inlet charge and prevent detonation. However, as boost increases, the turbocharger spins more revolutions per second, and heats up the air as part of its compression process. This reduces the effectiveness of the fuel as an air temp cooling method. This is where the capacity of a given turbocharger unit is taken into consideration. A larger turbo will be able to move similar quantities of air at less revolutions than a smaller turbo. As a result, the air is heated less. The larger turbo is thus considered to be \"more efficient\" than the smaller one. The drawbacks here are packaging (larger size incurs installation difficulties) and turbo lag time (the time it takes to reach maximum boost). Lag time increases due to increase in centrifugal mass.

Most manufacturers of turbocars equip their vehicles with smaller turbo units running low maximum boost, thus keeping air temps down. The smaller units also promote quick spool, thus providing the consumer with a good throttle response. Keeping the air temps down means less fuel is required, which helps manufacturers meet federal and state emmisions standards (or similar standards for other geographic markets). Typical boost levels range from 5-10 PSI using small to medium turbochargers.

A larger turbocharger runnig 8 PSI will have a colder air temp charge than a smaller turbocharger running 8 PSI. Since this air is colder, there is less expansion from heat by the time it reaches the cyllinder, and as a result the larger turbo packs in more air. More air means that more fuel is required. At lower boost levels this is handled by the computer. The computer can use MAP sensor readings to indicate boost, or an airflow meter to *estimate* boost. The resulting computer PSI determination is combined with air temp sensor readings to assess how much fuel is needed.

The computer is typically programmed to the limit of the factory equipment (pay special note here to injectors and fuel pressure). Once you go beyond the computer\'s programmed limits, you need a new way to deliver more fuel.


INTERCOOLING:

Intercooling also reduces the air inlet charge to help combat detonation. Depending on the size, it will more or less cool the air temp charge. Essentially a radiator used to cool the compressed intake air for the engine. The cooled air is denser and can provide more power and also reduces pinging/detonation. Intercoolers are used for both turbocharged and supercharged engines. Most intercoolers are air-to-air type, which means that ambient air is used to cool the compressed intake air. Less common air-to-water intercoolers use engine coolant to shed heat from the intake air. Turbocharged S12\'s do NOT come factory-equipped with an intercooler.

Something to note about intercoolers is that as compressed air passes through one, it experiences a pressure drop from the inlet to the outlet. Both size and tube design of an air-to-air intercooler core will determine how much pressure loss you will see. Flowbenching different intercoolers and comparing the flow rates will help show you how much or little this pressure loss occurs in different intercoolers. The design of the intercooler also affects how efficiently it draws the heat from the air temp charge. By the end of the air\'s trip through the intercooler, it has experienced pressure drop because of these factors. A larger turbo will be helpful in counteracting pressure drop on larger intercoolers because it can push harder with less heat generated.

A well intercooled engine will resist detonation better than a poorly intercooled engine because of the colder air temps. Paired with an efficient turbo, you will get much denser and colder air temps with steady boost pressure.

[Indecisive]

TUNING ETHIC

In the early days, as cars were tuned for higher performance, there were few ways for the human being to monitor the engine operations. Oil pressure, battery voltage, RPMs, water temperature. Not much else. Pushing these engines to extremes was tricky, and not much was available to track information other than temps and something called \"reading plugs\", where the sparkplug is frequently removed to inspect the color of the insulator (generally, an off-white to beige color indicates an acceptable mixture).

As cars became more advanced, computers were integrated, and *they* would monitor those same things, as well as even more data, such as fuel mixture (O2\'s), air flow (or air pressure), air temps, and a number of other things. There was no need for the human being to monitor these things as much since the computer took this data and managed the engine for you.

When you tinker with performance levels and go beyond the computer controlled limits, you now run a risk of damage from a poorly tuned vehicle. YOU are now responsible for monitoring engine data and making changes to componentry as needed to keep your engine running safely.

A good \"tuning ethic\" is one where you use available methods to monitor as many operations as possible as often as possible, and *SLOWLY* increase your engine output while doing so. Taking small steps means less risk should something not balance properly. It is a major aspect of a good tuning ethic.

So what methods for monitoring things are available?


MECHANICAL BOOST GAUGES:

Not all turbocharged cars are factory equipped with boost gauges. Those that are often use a comuterized gauge. This kind of gauge is typically there for the consumer to see when the car is at boost. Usually the computer displays boost on this gauge based on RPM, air temp, and air speed (or sometimes air density) data. This is an *estimation* on the computer\'s part. It is not always an accurate boost figure. Some cars have this kind of gauge but it does not even have numbered values on the gauge face! What use is that to performance tuners?

None at all. That is why your first and most important monitoring modification should be a \"mechanical\" boost gauge. This is a gauge that has a vacuum barb at the back, and a spring inside, that under either vacuum or positive presure (boost) moves a needle across the gauge face. The gauge face has numbers to indicate what PSI is required to push the internal spring that far (in other words move the needle).

A typical mechanical boost gauge (with both vacuum and boost readings):


This one can be had at Extreme Motorsports for $45:
http://www.extrememotorsports.com/g1cat/bstgauge.htm[/a]

Some mechanical boost gauges don\'t have vacuum readings, just boost. Most tuners prefer to have both vacuum and boost readings. It really depends on how much you want to monitor your engine. If you like to save gas and \"lazy drive\" your car (i.e. keep it out of boost condition as much as possible) most of the time, then you\'ll want a gauge that shows both.

A mechanical gauge uses no electronics to estimate boost, and instead tells you EXACTLY what boost is in the manifold. A vacuum line is connected to the back of the gauge, and usually T\'d into an existing vacuum connection AFTER the turbo, intercooler, and the throttle body. Usually this is somewhere on the intake manifold.

[Indecisive]

AIR/FUEL METERS:

Well, you can piggyback some of the computer\'s own sensors. One of the most popular to watch is the O2 sensor. An O2 sensor signal often only provides readable information at WOT. An O2 meter (also called an air/fuel meter) will show you what the WOT mixture is in terms of volts. Depending on the fuel mixture, the temperature of the O2 sensor will change. This inhibits or promotes electric current passage through the sensor. A richer fuel mixture will yield colder exhaust temps than a leaner one.

A couple common air/fuel meters:


More airflow meters can be seen at:
http://www.machv.com/cybairgaug.html[/a]
Some have more or less lights. You really only need to worry about a small range, because anything outside of that at WOT can mean trouble. Anything LESS than that range can result in immediate damage, and anothing above can result in eventual failure as well.

Some display an actual digital number value. These are the easiest to read.

Since the O2 sensor is at the end of an engine cycle, its readings are a delayed response to the actual real-time fuel mixture. As long as you are tuning 1 or 2 PSI at a time increases, this can be used without much risk.

It\'s a good idea to install this and run stock boost to determine a baseline voltage reading on your air/fuel meter (you should already have installed a mechanical boost gauge). If your stock boost is 8 PSI, and you check the air/fuel meter and it\'s at 9.5v, then now you know your baseline voltage. When turning up the boost, try to maintain that voltage at WOT throughout your RPM range. By doing so you maintain your safe air/fuel ratio.



EXHAUST GAS TEMP METER:

Another way to monitor the fuel mixture is through EGT\'s. EGT stands for Exhaust Gas Temperature. In the tuning world, \"EGT\'s\" usually refers to a gauge that displays the temperature perceived by a sensor that is either mounted on the outside of an exhaust manifold/header/etc. or via a probe that internally protrudes into the exhaust path. As fuel leans out, the exhaust temps increase. Likewise, as fuel richens, the exhaust temps increase.

Here is an excellent example of an EGT gauge from VDO (reading in Farenheight):


This one is available at Extreme Motorsports for $160.00, a good price, and complete with probe and related connections:
[URL=http://www.extrememotorsports.com/g1cat/egtgauge.htm]http://www.extrememotorsports.com/g1cat/egtgauge.htm[/a]

It is usually best to find normal/acceptable operating temps first before tuning for higher than factory boost. You get your baseline EGT reading just as you would find your baseline O2 voltage. Once you know this temperature, try to maintain it as you increase boost.



KNOCK LED:

Many turbocharged cars are equipped with a \"knock sensor\". This is a high-frequency microphone that is factory-tuned to listen for knock in an engine. Usually this signal is monitored by the ECU, for the purposes of advancing or retarding timing. Not all turbocharged cars use computer-controlled timing. If you have a cap and rotor ignition, you might not have computer controlled timing. Some cars have electronically-controlled boost (using an electric vacuum solenoid), and based upon the knock signal, the ECU can actually lower the boost.

Companies like MSD make devices that show knock in an engine. A knock sensor is typically screwed into the side of an engine block. Watching the LED display can show you when knck is occuring, and you can back off the throttle until you have safely retuned it.


READING PLUGS:

Yes, it\'s an old method, but it still works! Periodically removing and inspecting spark plugs will tell you quite a bit about how the engine is running. Color of the insulator will tell you if it is too rich or too lean. A darker orange means thee is too much fuel. A lighter white means too lean. A typical safe misture will produce off-white/beige spark plug insulators. the condition of the electrode will also tell you things. Deposits also give you some insight to the way the engine is running.

For a complete guide to reading plugs and what to look out for, visit:
[URL=http://www.centuryperformance.com/spark2.htm]http://www.centuryperformance.com/spark2.htm[/a]


DATALOGGING:

Datalogging is something of a fairly new science in performance automotive. Until the past few years, only the manufacturer was able to tap into and evaluate data obtained by the car\'s computer. This was necessary to develop more advanced cars that output more power with smaller engines.

The data collecting capabilities of these computers has always been present, however there has never been a clear-cut option by the owner/driver to access this data. In some cars, the manufactuerer generously included quick-read features that flashed engine check lights and other lights when the driver turned the key back and forth a number of times, or held a pedal in for a certain length of time.

The automotive repair industry quickly offered aftermarket computers to evaluate engine error codes, however these were expensive. They also didn\'t work well to evaluate engine performance beyond factory specs because they did not observe real-time sensor data (they only picked up engine error codes)

Then along came the datalogger. This is essentially a device that extracts the recorded data (error codes), as well as displays (and typically records for playback) real-time data from all the sensors in the car.

The typical datalogger consists of a cable (one end shaped to fit into the car computer\'s recepticle, the other end a DB-9 PC-serial interface), software, and a personal computing device.

With this setup, you can watch O2\'s, knock sum (the ECU can get a value of how many occurances of knock is heard in an interval of time, and retard timing/boost/add fuel), timing advance/retardation, air temps, injector pulse widths, and corresponding RPMs. Now you know exactly what is going on in the engine at whatever RPM you choose to look at. The real-time viewing is especially usefull in saving your engie when you get excessive knock (you can back off the throttle when you see high knocksum or massive timing retardation).

A datalogger is very useful when tuning cars with something like Apex\'i\'s Super Air/Fuel Converter (new-style with graphic display):
This is a device that lets you alter the fuel delivery +/-20% per 1000 RPM range. You *could* possibly do this via EGT and O2 readings, however since the S-AFC works in RMP ranges of 1K, and it involves complex settings, it is not recommended without some way to datalog engine sensor data and operations, either real-time or otherwise.


CONCLUSION:

A good tuning ethic involves the use of gauges, patience, knowlege of turbocharged systems, fuel injection, basic 4-stroke combustion operations, and a good deal of knowledge about the specific car platform you are working with.