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Author Topic: What the hell is: TUNING?  (Read 3302 times)

Offline Arro

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What the hell is: TUNING?
« on: 02:10:11 AM / 13-Apr-12 »
I wrote this article in the first month of Club-S12, as a compilation of some posts I had put up in the predecessor to this place (the old "Classic 200SX" mailing group). It has been handed down through this or that post, intact and unaltered. I wanted to repost it here, with some very minor revisions.

It's more or less universally applicable to any tuning scenario, and while there may be other elements not discussed, it is intended to give a balanced education in basic tuning concepts for modern automotive performance (and not a comprehensive list of all available techniques).

This was the article that inspired the "What the hell is that?" section from the beginning... a collection introductory-level of tech articles designed to educate those new to auto tuning and tech.

Thanks to Dan Aho (Dan0myte), and to Tim and Travis (Indecisive & westside27375) for preserving it all this time. -Arro

Originally authored 6/02, revised 4/13/12

What the hell is TUNING? - Arro,

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 describe alteration of a musical instrument, your car shouldn't be too different in definition. 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 carbureted environment, with no computers and mostly just mechanical and pneumatic (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 carbureted days.

Later, forced induction was introduced to these carbureted systems, using superchargers (belt-driven blowers) and turbochargers (exhaust-driven blowers) to pack in more air than natural aspiration would draw in normally. This "forced induction" was limited because tuning with carbs wouldn't allow for easy fuel mixture changes as forced induction changed conditions, so pushing more air into an engine was a very limited method, and only for serious performance.

Today, the concept of "tuning" is more more complex, involving head 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 performance without altering and testing components, experimentation and safety become chief 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 cylinder engines, since these are the most abundant, and manufacturers have offered them in more and more amazing options.

THE BASICS: Natural aspiration vs. forced induction.

In the naturally-aspirated end of things, these cars generally have close-tolerance valving (sometimes even trick valving like Honda's VTEC/iVTEC 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. 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 and as well as reliability and longevity for mass-production. By safely going beyond the manufacturer-configured output, you can increase your potential power and push the engine to its *actual* limits. You can even increase its limits if your ambition (and your wallet) can handle it.

In forced induction (turbocharged and supercharged engines), more air is stuffed into the engine, and more fuel, providing more bang. It sounds simple, but there are other factors to consider, such as the strength of the components, fuel mixtures, and keeping things safe (i.e. keeping your engine from going BOOM!). We'll cover both naturally aspirated tuning and forced induction in this article.

NATURAL ASPIRATION: It's about port size, lift, duration, and free-flowing intake and exhaust.

Naturally aspirated engines draw in their air by means of the vacuum produced when the pistons are in their intake stroke. The intake valve opens as the piston starts to move downward, and essentially the piston "sucks in" the air through the intake port and into the engine's cylinder. This is considered "natural" because it is a normal process when the pistons move down with the intake valves open (air just gets sucked in). Increasing port size can increase the amount of air that can be sucked into the cylinders naturally. So can changing the lift of the valves (how far they open). This is generally attributed to the camshaft lobes, which are egg-shaped sections of a rotating shaft. In older engines these are mounted low and use long rods to control the valves up top, but on more modern engines (especially 4 and 6 cylinder engines) these are located directly on the top of the head. Another way to improve airflow into the engine is to change the duration of the valves (how long they stay open for a cycle), and this is also expressed as a specification of the camshaft. Similarly, both lift and duration can be changed on the exhaust ports, making it easier for the engine to push out the exhaust gasses on that cycle. Making it easier for the engine to ingest air and push out exhaust means the engine can rev up faster, and its power limitations are raised to higher levels due to less resistance. In essence, this is the goal of naturally-aspirated performance.

While the workings of the engine can be tweaked for more airflow and performance. The intake air path leading to the head can be improved. Revised intake manifolds and intake air pipes can be swapped in for less restrictive air flow, as can higher flowing air filters. In the same manner, better exhaust manifolds such as high-flow headers and higher-flowing exhaust systems can improve exhaust flow, as can improved muffler designs and catalytic converters (or their removal). Improving how easy air gets into the engine, and how easy exhaust gets out.

As a more aggressive approach, pistons can be swapped out for higher compression ones. While the piston moves downward and injests air, a carbureter or fuel injector sprays a fine mist of fuel into the air right before it rushes into the head port. After a piston pulls downward and ingests air and fuel mixture into the cylinder, the next step is when it moves upward again towards the head. When it does this, it is compressing the air/fuel mixture. Once the piston reaches the top of its compression, it starts to move back down again. The spark plug ignites the air/fuel mixture a fractional moment after the piston begins its downward travel, and the resulting explosion shoves the piston down. This is the "power" of the engine. This is what "makes it go". Switching out pistons for ones that compress the air/fuel mixture more than stock means the tightly packed air will explode with more force (produce more power).

Compression in a cylinder pushes the air and fuel molecules together. This means they get packed closer, and "bump" into each other causing friction. The friction causes heat. Too much heat will ignite the air/fuel mixture prematurely. If the piston is still moving upward when this happens, the results can be catastrophic. The easiest way to change this is to use higher octane fuels that can take more heat (and won't ignite until the spark plug does it), and to add more fuel which also cools down the air some and slows the motion of the air/fuel molecules (meaning less friction, and in turn, less heat). Most modern factory fuel systems have some flexibility, but the computers are limited, as are the capacity of the fuel injectors. Switching to a really high compression piston set usually requires modification to the fuel system... bigger fuel injectors, a larger fuel pump to feed them, maybe a beefier fuel pressure regulator (or an adjustable one), and possibly a more advanced computer to control a greater range of fuel delivery needs. Sometimes this is not enough, and fuel systems need to be manually tuned by human beings.

FORCED INDUCTION: Supercharging and turbocharging.

In the turbocharged and supercharged world, many of these modern engines take well to forced induction, and the computer control along with computerized and high-tech aftermarket componentry allow for more useful levels of boost without compromising reliability. Ingenuity 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 cylinder compression with a change of pistons. The dynamic (or changing) "compression" in a cylinder under *high* boost is (at its maximum boost moment) far above the static (fixed) compression in high compression 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).

In factory supercharged and turbocharged engines, the computers are designed with this in mind, and have more flexibility towards adding and removing fuel. They also tend to have larger injectors because of this, and sometimes higher flowing fuel pumps, beefier fuel pressure regulators, and additional sensors to monitor air temps, exhaust content (to observe what fuel is NOT burned off as a way to determine the mixture going into the engine), and even knock sensors to detect minor detonation (air/fuel ignitions that happen at times other than when the spark plug fires). So along with beefier internals, there are usually electronic and fuel delivery components designed with turbocharging in mind.

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. It's the same process as performed by the factory electronic fuel system, only done with either an aftermarket computer capable of more range, or manually by human configuration. Or by both. This is the basic idea in tuning a boosted engine for more power.

First and foremost when tuning a boosted engine is fuel mixture. In most modern supercharged and turbocharged vehicles, the computer monitors fuel mixture via O2 readings from the "oxygen sensor" (also called an O2 sensor).


Also called an "O2" sensor. This is a 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. Naturally-aspirated engines have these, as do supercharged and turbocharged engines, although they are far more vital on the boosted setups. Many factory turbocharged vehicles mount the O2 sensor in an "O2 housing" that sits between the turbocharger's exhaust outlet and the downpipe. For example, the CA18ET-equipped S12 cars have the O2 sensor on the O2 housing. For CA20E-equipped cars, it is in the exhaust manifold.


In most super and turbocharged cars, the computer uses the oxygen sensor, along with air temp sensors and either an airflow meter or a "manifold absolute pressure" sensor (MAP for short) to monitor the air flow into engine. The O2 sensor tells the computer the fuel mixture, 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. If the PSI in the intake air exceeds the computer's range of fuel for open loop (known as the fuel map), the result is what is called an "overboost" condition. This is where the positive pressure from the turbocharger exceeds the factory-tuned limitations of the engine and supporting fuel system. Most factory boosted vehicles have countermeasures to prevent this.


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. The former method is considered "intelligent" because the computer determines when to shut things down based on sensor input (usually the air/flow meter or MAP sensor). The latter method is considered "mechanical" because there is no computer evaluating sensor data, just a physical process.

A "pop-up" valve (or "PUV") is a mechanical safety device on the intake manifold of some older factory boosted cars. On a CA18ET (turbo) S12, there is a PUV on the intake manifold 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. Some factory supercharged vehicles use a very similar device called a "bypass valve" to prevent the same thing.

If you want to go over the factory boost level, the first thing you must do is permenantly seal this valve (or remove it and plug the hole). This effectively defeats the overboost safety feature in a vehicle with a mechanical overboost device. This also means that you are now able to force more air than the stock fuel system can support, and risk damaging your engine.


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.


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.


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 emissions standards. Typical factory boost levels range from 5-10 PSI using small to medium sized turbochargers.

A larger turbocharger running 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 cylinder, 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. This is more of an open loop (and fuel map) process, as closed loop will read the O2 sensor to get a true (if delayed) fuel mixture reading and adjust accordingly.

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.

FUEL UPGRADES: More juice for more bang.

Stock fuel systems on fuel-injected cars have modest-sized injectors, fed by a fuel rail, which is pressurized by a modest fuel pressure regulator (or "FPR"). This is in turn fed by a similarly modest fuel pump that is usually located inside the fuel tank itself. Vehicles that are turbocharged from the factory are usually equipped with larger fuel injectors, an FPR with a stiffer spring (more pressure), and a higher-flowing fuel pump, but when you turn up the boost past factory levels this may still be insufficient. Switching to larger injectors will be a start, but they need to be fed more fuel by a stronger fuel pump. However, too strong of a fuel pump will overrun the stock FPR (it will defeat the spring), and you won't be able to control your fuel properly. This means that adding a larger aftermarket fuel pump may require you to upgrade the FPR as well. It is, after all, a total system.

Sometimes you can get away with modestly larger injectors, a slightly more powerful fuel pump, and your stock FPR. It just depends on your choice of upgraded components. Either way, the fuel you need will be dictated by the boost you want to run and the supporting modifications.


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 it is similar to your radiator, only instead of passing coolant through it, it is 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 coolant to shed heat from the intake air. Most cars do NOT come factory-equipped with an intercooler, and those that do usually feature a smallish one that can only handle the minimal heat of a small factory turbo.

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 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.


Getting a turbo spooled up quick is important to getting more grunt out of your engine. A longer spool time means a longer delay in maximum power. Also, a larger turbocharger takes longer time to spool up because there is more centrifugal weight to get spinning. One of the easiest ways to improve the spool time of a turbocharger is to open up the exhaust system behind (after) the turbocharger. Exhaust systems have a level of backpressure. As you increase the flow capacity of an exhaust system, the back pressure decreases. You want some backpressure on an engine... a discussion on this point is lengthy and better left to another time and place, but for now just understand that a bit is good for the engine. Too much is not. A turbocharger is basically a super-restrictive bottleneck on exhaust -- far more than a typical exhaust manifold. This is because it is not only acting as a collector, but also further restricts the flow of the exhaust as it passed through the exhaust turbine. As with the concept of backpressure, the operation of a turbocharger is another subject in its own right, but for tuning purposes, we are focusing here on the restrictive nature of a turbocharger.

This restriction creates massive backpressure inside the exhaust manifold (or turbo header), between the exhaust ports of the head and the turbocharger. Because of this, anything you can do after the turbocharger is a good idea. The wider the exhaust, generally the better the spool, because the more open back end will promote exhaust to rush out through it. Also, a larger diameter exhaust system after the turbo will allow for more heat expansion, which will help speed the exhaust out towards the tailpipe.

While it is true that more open is generally considered "good", a smaller turbo with a huge exhaust will spool up so fast that it will have massive spike, which is when the boost jumps past the set boost level. This could result in boosting beyond your fuel mixture (i.e. risk of damage). Really small turbochargers will not only spike, but may even spool out of control. There is also a concern of boost creep, where the turbo settles at its max boost setting, but as throttle keeps up, the boost level slowly creeps up past the maximum setting (again, with risk of damage). The solution to this is usually to modify the existing internal wastegate for more flow (thus, more control over the turbo spool) or to use an external wastegate unit that flows more and with better control.

Spool time is just half of the battle with turbo performance. Keeping the spool is important for keeping the power between shifts. When you back off the pedal to shift gears in spirited driving, the throttle plate closes quickly and boost slams into it. This boosted air has nowhere to go except backwards through the turbocharger's outlet (back out the way it came). This obviously slows the compressor spin (or stops it entirely) in a process called "stacking". Some factory turbocharged cars come with a blow-off valve to reduce this stacking (although they call it a "bypass valve" because it usually dumps back into the intake airstream). Installation of a blow-off valve (or a "bypass valve" in some cases) allows the boosted air to temporarily vent elsewhere when the throttle body plate shuts, and allows the turbo's compressor wheel to keep spinning unhindered. When you get into the next gear and hit the throttle again, the turbo is already spinning close to where it was before, and spooling back up to maximum boost is almost instant.

A typical blow-off valve (with "bypass" routing option) as installed on an intercooler pipe:

Routing the blow-off air back into the airstream is done usually for airflow-metered setups, and dumps the air back into the airpath BEFORE the turbocharger and after the airflow meter. Some people choose to simply dump the air out to atmosphere (the engine bay), as this is sometimes perceived as better for keeping spool. On airflow metered cars, venting to atmosphere may result in some issues with idle or when slowing down to idle, or there may be not.

There are of course larger aftermarket BOV's that allow adjustment of the spring tension (to alter release speed and timing), as well as larger valves for more airflow (better retention of spool), and some are designed to dump either to atmosphere or reroute back into the air intake before the turbo. Some are only designed to dump to atmosphere. Most of the aftermarket versions can be disassembled for cleaning and maintenance.

Ok, so now you understand about what makes an engine more powerful. But how do you do that *safely*?

TUNING ETHIC: The right way to do things (i.e. how not to blow your motor up).

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 spark plug is frequently removed to inspect the color of the insulator (generally, an off-white to beige color indicates an acceptable fuel 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?


Not all turbocharged cars are factory equipped with boost gauges. Those that do come with them often use a computerized 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 pressure (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):

The vacuum shows normal aspiration (in Hg), and the turbo reading shows boost (in PSI). Some gauges only show boost and are usually labeled "BOOST" instead of "TURBO", but for the best tuning, you will want to see both vacuum and turbo boost operations (as is shown in the pictured gauge). Most experienced 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. Ideally you want it as close to the engine's intake ports as possible.


Monitoring the fuel mixture is also important. You can piggyback some of the computer's own sensors to do this. 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:

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 anything above can result in eventual failure as well.

Some display an actual digital number value. These are the easiest to read, but as expected they will cost more.

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.

If you are planning to turn up the boost on a factory turbocharged vehicle, it's a good idea to install this first 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.

If you are planning to turbocharge a vehicle that came non-turbo from the factory, installing this gauge first (BEFORE bolt-ons like turbocharger, injectors, etc.) and taking readings can also show you where you need to return the fuel once you start boosting and adding fuel. A balanced mixture is pretty much the same regardless if you are boosted or not. This ideal mixture is referred to as stoichiometric (or just "stoich").


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 elsewhere. Sometimes this is called a "pyrometer". As fuel leans out, the exhaust temps increase. Likewise, as fuel richens, the exhaust temps decrease. The EGT gauge measures this electrically.

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

Some gauges read in metric (Celsius), so it will be a matter of preference.

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. Baselining also means you can run with either a Fahrenheit-based or Celsius-based gauge and get the same results.


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 knock is occurring, and you can back off the throttle until you have safely re-tuned the fuel mixture.


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. The color of the ceramic insulator will tell you if the fuel mixture is too rich or too lean. A darker orange means thee is too much fuel. A lighter white means too lean. A typical safe mixture 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:


Datalogging is something used by the amateur tuner only in the past decade or so. Before that, only the manufacturer or professional tuning shops were 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, or in the case of professional tuning, to produce competitive performance race cars.

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 manufacturer 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 receptacle, the other end a PC's serial or USB 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 occurrences 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 useful in saving your engine 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 (or "S-AFC" as it is best known):
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.


On-Board Diagnostics (or "OBD") is a standard in engine management that was intended to improve auto emissions, as well as make certain engine control functions standardized across the automotive industry. OBD-1 was largely a failure in that there were numerous technical problems and not enough cooperation between auto manufacturers.

OBD-1.5 was a transition where some advanced features that would later be in OBD-II were incorporated. An example in the Nissan world of this would be the 1995 Nissan KA24DE engines, which featured the simplicity of OBD-1 sensors, but diagnostic routines (and a diagnostic port) that would be later used in OBD-II.

OBD-II was the final result of the previous incarnations, and standardization was at last a reality. Unfortunately, OBD-II computer systems are so good at managing engines that sometimes modifications are defeated by the engine control unit (the "ECU", or the computer if you will). This is especially true in OBD-IIB systems (sometimes called next-generation computers or "NGC"). How much or little control the OBD-II computer differs from make and model.

One advantage to OBD-II systems is that they all have standard data records, and a standardized data port. Therefore, OBD-II scanners will work on any OBD-II equipped vehicle, as will more advanced dataloggers. There are even newer datalogging systems that use a Bluetooth (wireless) connector with your computer or even your mobile phone to monitor all sensors in both real time and recorded progress. Obviously this is very useful to the performance tuner!

ENGINE MANAGEMENT: Independence from the OEM.

The most extreme (and flexible) approach is to avoid "piggyback" computers (like the S-AFC) that just modify the factory computer's inputs and outputs, and simply go with a completely aftermarket engine management setup. AEM makes the EMS, a popular aftermarket engine management replacement that can be preloaded with values for many popular engines. Other companies such as Motec and Megasquirt have total engine management solutions available, and there is considerable support for all of the major brands on the internet. Aftermarket engine management systems can use all the stock sensors, or can use other sensors not originally included. They can even eliminate some sensors entirely. The setup is flexible, and the limit is with the tuner's choice (and expertise). These are NOT for the amateur. While a professional (or an educated tuner) can make use of the advanced features, a novice or even an amateur probably does not have the know-how to use these kinds of systems without serious risk. With patience, piggyback computers and do-it-yourself methods can yield great results, but in an easy to understand environment.


A good tuning ethic involves the use of gauges, patience, and an understanding of fuel mixtures. This is especially true with turbocharged systems, where fuel injection, basic 4-stroke combustion operations, and a good deal of knowledge about the specific car platform you are working with will help you safely get more performance out of your car. Baselining readings goes a long ways towards preventing mishaps.... only a fool rushes in and bolts on this or that performance part, or just turns up the boost (or someone with a lot of money to pay for a dyno tune... or an engine rebuild!). It's not hard to tune your own car, as long as you have the patience to do so with the right tuning ethic. You don't need to pay a shop to build and tune your engine for more power as long as you understand the basics and use patience and prudence when upping the power.

Rev. 4/13/12

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-Jason Arro

'85 Nissan 200SX (KA24DE)
'85 Nissan Silvia RS-X - FJ20 w/ dual Weber carbs
'84 Nissan 200SX Turbo
'85 Nissan 200SX Turbo
Drive it like you stole it, and work on it like you married it - self quote
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Hella flush and all associates should be gunned down for brainwashing people into thinking a 225 and lots of camber is proper wheel fitment. THAT IS EASY, anyone can camber a skinny as tire till it dosnt rub. Now fitting an 11 with a 315 on stock fender with reasonable camber, that is fitment. And looks, and performs better than both.
i dont own a s12 at the moment but trying to acquire one to get rid of my s13 hatch
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[27:54] zastaba: I had a friend touch the contacts on his distributer once
[28:04] zastaba: He did the super jumping up and down pain dance