Tuning can be an intimidating topic and the verbiage tossed around difficult to comprehend. So, let’s get you familiar with it. You may ask, “Why should I learn any more than I need to know if I am converting to EFI anyway?” Quite simply, this is one of those topics that you simply can’t know enough about. Since most EFI systems put the power to tune in the palm of your hand, you really should know what you’re doing before pressing buttons. And guess what? It really isn’t that hard.
This Tech Tip is From the Full Book, EFI CONVERSIONS: HOW TO SWAP YOUR CARB FOR ELECTRONIC FUEL INJECTION . For a comprehensive guide on this entire subject you can visit this link:
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This chapter gives you a good understanding of the basics and introduces you to some of the vocabulary that accompanies engine tuning. For an in-depth study on EFI tuning, pick up a copy of Engine Management: Advanced Tuning by Greg Banish.
Stoichiometry is the chemistry that defines the relationship between the air and fuel in an engine. Metering the correct mass of fuel based on the mass of the air entering a given engine is the primary job of any EFI system. Numerous factors determine the correct air/fuel (A/F) ratio, including fuel type, engine load, and engine efficiency.
Different types of fuels have different ideal A/F ratios. An ideal A/F ratio with a given fuel means that the exact mass of air is flowing into the engine to burn 100 percent of the fuel in the combustion chamber. This is often referred to as stoichiometric or stoic.
As you drive around, the engine has various loads placed on it. Some are easy, some are more difficult and changes in MAP accurately reflect this. As MAP increases (measured in inches of mercury or kPa), a richer mixture is needed. The opposite is true as MAP decreases.
Any true performance car should have a vacuum gauge visible from the driver’s seat so that you can gain an understanding of how your particular engine responds to loads placed on it as you drive around.
For naturally aspirated engines, maximum efficiency is achieved at 3 to 5 percent leaner than stoic, and maximum power is achieved at 10 to 15 percent richer than stoic. Precisely where is specific to the engine combination and the types of loads it is subjected to.
For a given fuel, the relationship to a given A/F ratio with respect to its stoic ratio is defined as Lambda and can be expressed by the Greek letter λ. For example, consider the chart below.
So, Lambda is just a simple way of comparing actual A/F ratio with a given fuel’s stoichiometric value. This can be really handy when using a wideband A/F meter to determine the actual A/F ratio and then using that data to make changes in the Target Air/Fuel Ratio Table in the software (see Chapter 6 for more details). Interestingly enough, the British refer to oxygen sensors as Lambda probes.
Igniting the A/F mixture in each of the cylinders is the job of the ignition system. In a four-stroke engine (intake, compression, power, exhaust), ignition occurs after the intake stroke and during the compression stroke before the piston reaches top dead center (TDC). As the mixture burns, force is exerted on the piston, forcing it down in the cylinder (the power stroke), rotating the crankshaft, and creating torque in the process.
Ignition timing is a measure of degrees before top dead center (BTDC) at which the spark event occurs. For example, 34 degrees of timing means that the spark event occurs in the first cylinder in the firing order at 34 degrees BTDC.
Let’s be a little more specific and include valve events so that you get the complete picture of the beauty of the internal combustion engine. Valve timing is a function of the camshaft, which makes one complete revolution for every two revolutions of the crankshaft. The specifics of the camshaft determine when the intake and exhaust valves open and close with respect to the location of the piston in the cylinder.
Intake Stroke: Intake Valve Open
The piston moves downward in the cylinder with the intake valve open. As the piston moves downward in the cylinder, the pressure in the cylinder is lower than the pressure in the intake manifold. This causes the A/F mixture in the manifold to enter the cylinder.
Compression Stroke: Intake and Exhaust Valves Closed
After reaching bottom dead center (BDC), the piston then travels upward in the cylinder compressing the A/F mixture in the process. At some point before the piston reaches TDC, the spark plug ignites the mixture.
The spark must be timed so that the piston is forced downward by the pressure created by the burning mixture. If the spark occurs too soon, incredible pressure is exerted on the top of the piston because it hasn’t finished the compression stroke; the burning mixture is working to force it in the opposite direction. This causes detonation (which sounds like marbles in a tin can) and is a recipe for the death of any internal combustion engine. If the spark occurs too late, power is lost.
Power Stroke: Intake and Exhaust Valves Closed
After the mixture has been ignited, it begins to burn. As the burn spreads in the cylinder, the cylinder pressure rises quickly and forces the piston downward in the cylinder. When the piston is forced down in the cylinder, it rotates the crankshaft, producing torque.
Exhaust Stroke: Exhaust Valve Open
After the piston reaches BDC on the power stroke, it returns to TDC on the exhaust stroke with the exhaust valve open. As the piston moves upward in the cylinder, it forces the spent gases from combustion out the exhaust valve and into the exhaust system.
Repeat. What a thing of beauty!
Exactly when the mixture is ignited while the piston is on the compression stroke is a function with many variables, including octane rating of the fuel, combustion chamber volume and design, piston type, cylinder head specifics, compression, load on the engine, and economy versus performance.
Let’s discuss only octane rating, load on the engine, and economy versus performance and leave the others to the engine builders.
Octane Rating: Different fuels have different octane ratings. Lower-octane fuels are easier to ignite than higher-octane fuels. This goes against conventional wisdom, doesn’t it? For example, premium gas in the state of Arizona has an octane rating of 91 while E85 has an octane rating of between 100 and 110 depending on who you ask. Kind of easy to see why E85 has gained so much attention by hot rodders now, huh?
Fuels with lower octane ratings, such as regular gas, require less ignition timing to complete the burn while fuels with higher octane ratings, such as premium gas, require more ignition timing to complete the burn. If you pay the extra money for premium fuel, your engine should have additional timing in it to take advantage of the extra horsepower that can be gained from using it.
Load on the Engine: As the load on the engine increases, less timing is required to ignite the mixture. This is due to the increased pressure in the cylinder.
Economy versus Performance: The best engine tuners are able to create a timing curve for a particular application that allows the engine to burn the maximum percentage of the mixture with respect to RPM and MAP. The greater the percentage of the mixture that is burned, the greater the efficiency of the engine. This is a function of the A/F ratio, RPM, and the load on the engine. The beauty of any EFI system that performs fuel metering and ignition timing is that you can quickly modify the A/F ratio and timing with respect to each other in an effort to quickly achieve the highest efficiency.
Operating Mode and Sensors
All but the most basic ECUs can operate in one of two modes: closed loop or open loop. While in closed loop, the ECU can also be set to learn. Let’s discuss these each in detail.
When the ECU is operating in closed loop, it uses the feedback provided from the oxygen sensor(s) to make changes to the Base Fuel Table to achieve the values in the Target Air/ Fuel Ratio Table (hereafter referred to as the A/F targets). Changes are either adding or removing fuel and factored as percentages.
The Learn function is a powerful tool when the ECU is operating in closed loop. Quite simply, when Learn is enabled in laptop-tunable ECUs, the percentage differences are stored in the Learn Table (typically a read-only table). As the vehicle is driven, the Learn Table is continually mapped, remapped, and percentages continually refined in an effort to achieve the A/F targets in all cells of the Target Air/Fuel Ratio Table. The value in the Base Fuel Table and the value in the Learn Table are factored in by the ECU to arrive at the correct amount of fuel.
For example, consider the following at a given RPM and MAP:
Learning can be intentionally slower at low RPM and intentionally faster at high RPM. This allows the data collected in the Learn Table to be a better reflection of the changes that need to be made to the Base Fuel Table to achieve the A/F targets.
Ideally, the actual A/F ratio as measured by the oxygen sensor(s) ends up within a few percent of the A/F targets. In addition, the Learn percentage in most laptop-tunable ECUs can be user adjusted from OFF to 100 percent. At 100 percent, the ECU can make large changes to the value of any cell in the Base Fuel Table in an effort to achieve the A/F target. When the Learn mode is OFF, the percentage difference between the value in the Base Fuel Table and the A/F targets is not plotted in the Learn Table. Depending on the application, it may be desirable to disable the Learn mode based on RPM, throttle position, etc.
Obviously, none of this is possible with a carburetor.
When the ECU is operating in open loop, it is not looking at the feedback provided by the oxygen sensor(s) to correct the values in the Base Fuel Table to achieve the A/F targets. So, when would you ever want to do that? Anytime that you want the ECU to ignore the feedback from the oxygen sensor(s), such as when using a low-RPM rev limiter such as for a transbrake or line lock. As the ignition intentionally misfires the cylinders to keep the engine within a certain RPM, you don’t want the ECU leaning the mixture because of the unburned fuel in the exhaust.
In addition, you may want to fine-tune specific areas of a tune in open loop. For example, engine and chassis tuners may elect to tune in open loop and rely on external wideband A/F meters in an effort to avoid the ECU making automatic changes. This allows them to make changes to the tune as they see fit to achieve their goals.
Depending on the software, you may have a lot of control over the closed loop, open loop, and Learn parameters. This provides all kinds of tuning flexibility.
Regardless of whether the system is operating in closed or open loop, the ECU has the ability to adjust the tune based on feedback from other sensors. Most aftermarket systems can be set up to do this automatically.
CTS: When first starting the engine, a richer mixture is required to keep the engine idling smoothly. The ECU can be programmed to enrich the mixture and then slowly lean the mixture as the engine warms up to operating temperature. It does so via the feedback from the CTS. This is similar to the function of the choke of a carburetor.
As the engine temperature rises above the ideal operating temperature, it is beneficial to reduce the ignition timing to stave off detonation. This is also done via feedback from the CTS, although this feature is only available on systems with engine management.
IAT: As the temperature of the ambient air decreases, the air becomes denser as it has a greater mass of oxygen. As the temperature of the ambient air increases, the air becomes less dense as it has a lower mass of oxygen. The ECU tracks the IAT and can automatically enrich or lean the mixture based on temperature changes.
BP: Some aftermarket ECUs have a barometric pressure sensor to monitor barometric pressure. The ECU tracks the barometer and can automatically enrich or lean the mixture accordingly.
TPS: The ECU monitors the position of the throttle constantly. When the throttle is quickly depressed, the ECU knows to enrich the mixture to prevent a lean bog. This is similar to the function of the accelerator pump on a carburetor.
In addition, the ECU tracks the throttle position in an effort to manage the IAC. The IAC is the key to achieving a smooth idle. As you know, when the throttle blades of a throttle body are fully closed, as they are at idle and when releasing the throttle, the IAC manages the airflow into the engine. Some ECUs do all of this automatically in the background with no influence from the user. Others allow the user to fine-tune the IAC via the software.
Depending on the particular system, you have access to some parameters that allows you to influence the overall drivability of the vehicle. Basic EFI systems that perform fuel metering only typically allow you to fine-tune the Acceleration Enrichment (AE) to eliminate bogs on throttle transition. Laptop-tunable EFI systems, and those with engine management, allow you to fine-tune a number of parameters, including (but not necessarily limited to) the relationship of timing and A/F ratio and the operation of the IAC.
Acceleration enrichment allows you to tune out bogs as a result of throttle transitions or changes in manifold pressure. The MSD Atomic EFI system we install in Chapter 5 has two such user adjustments: Pump Squirt and Power Valve Enrich. The Pump Squirt feature functions very similarly to the accelerator pump of a carburetor, adding fuel as the throttle position changes. The Power Valve Enrich feature allows you to add fuel as the load on the engine increases, which is monitored via the MAP sensor (this can vary widely via camshaft profile as well). Engine load is not always a function of the position of the throttle. For example, you may be cruising down the highway at 70 mph at a given throttle position. As the grade increases, the load on the engine also increases even though throttle position hasn’t changed.
These simple adjustments allow you to calibrate the Atomic EFI system while you’re driving the vehicle, but it’s safer and better for the passenger to make the adjustments. The net result is that you can quickly achieve the smoothest drivability with a few presses of the buttons on the handheld controller.
Most laptop-tunable EFI systems allow far greater control over the AE. The Holley HP and Dominator EFI systems we install in Chapter 6 allows you to finely calibrate it as follows:
- AE vs TPS Rate of Change
- AE vs MAP Rate of Change
- AE vs Coolant Temperature
- MAP AE Time vs Coolant Temperature
- AE Correction vs TPS
- MAP AE vs Coolant Temperature
It takes a bit of knowledge and practice to perfectly dial in the acceleration enrichment for these systems. This is definitely an area at which an experienced tuner can be worth their weight in gold.
Ignition Timing to A/F Ratio
Any EFI system with engine management allows you to adjust ignition timing in relation to A/F ratio. In the idle and drivability areas, you realize the best fuel economy with the correct engine timing with respect to the A/F Ratio at a given RPM. This can take a bit of trial and error to achieve. If the engine surges at any RPM in the drivability area, this can be an indication that the relationship between timing and A/F ratio is the culprit (see Chapter 5 for more details).
Fine-Tuning the IAC
Achieving the correct relationship between the IAC and the throttle-blade adjustment is the key to a smooth idle. Once you’ve set the throttle-blade position, the ECU manages the IAC position so the correct mass of air enters the engine at idle based on atmospheric conditions. Laptop-tunable EFI systems allow you to fine-tune the IAC to achieve the smoothest idle, smoothest transition from idle, and smoothest transition back to idle.
If you’re a first-time tuner, you’ll find it comforting to know that any changes you make that do not have the desired results are quickly and easily reversed. I sometimes take a picture of the settings with my smart-phone before making changes. That way, I can easily get back to the original settings if what I thought would work, didn’t.
Tuning Tools of the Trade
Any serious carb tuner has a bevy of specific carb-tuning tools as well as a bunch of parts that can be swapped within the carburetor in the tuning process. The good news here is that EFI systems don’t require any tuning parts, so to speak, but if you intend to do your own tuning and you want to achieve the best drivability and performance, you really should consider investing in the following tools.
Wideband A/F Meter
The cost of a quality wideband A/F meter has come down to a point where any enthusiast can now afford one. They are offered in single-channel (one oxygen sensor input) and dual-channel (two oxygen sensor inputs) units. Some have the ability to connect several more oxygen sensors for the nth degree in tuning. At a minimum, you want a single-channel unit with the ability to also track RPM.
Nicer units also afford you the opportunity to input any 0-5V sensor (TPS, IAT, CTS, MAP, etc.) by interfacing an included or optional harness with those sensors. Another nice feature is the ability of the meter to make a datalog of all inputs connected to it.
Oxygen Sensor Weld Rings
No matter what EFI system you ultimately settle on, it’s just good planning to have the exhaust shop install oxygen sensor weld rings (oxygen bungs) in both sides of the exhaust at the same time, even if the system you’ve got your eye on has only a single oxygen sensor. The standard thread size is 18 mm. Most wideband A/F meters, wideband A/F gauges, and EFI systems include these, but you can also purchase them separately from numerous companies.
If you’re looking at an EFI system with dual wideband oxygen sensors, you need to have a minimum of three weld rings installed to give you some options down the road. You’ll thank me later.
Many laptop-programmable ECUs have internal datalogging capabilities. If you’re looking at one of the entry-level EFI systems, this is typically not available. Datalogging allows you to collect data in real time while you’re driving the vehicle in an effort to maximize the tune. This can be super handy to diagnose a drivability issue or optimize the tune to realize the peak performance of your engine.
If the ECU offers it, make sure that you become familiar with how to use it. If the EFI system you’re considering doesn’t offer datalogging, many quality wideband A/F meters do offer this, so you can kill two birds with one stone.
If you’ve read either of my automotive electrical books, you know how much of a stickler I am for a good DMM. A quality DMM with a MIN/MAX scale can be used to quickly diagnose charging system problems, fuel delivery problems, etc. Most of my car buddies are amazed at the data I can ascertain with one of my trusty Fluke meters. They watch in awe . . . it’s not that hard; really it isn’t! I use the Fluke 87 and 88 meters, but at minimum you should consider a 115.
Thus far, I have focused on naturally aspirated combinations. But what if you’re a power adder kind of enthusiast? I certainly am. Regardless of the power adder that you run, this is where the power of engine management proves to be incredibly valuable. Allowing the ECU to manage the timing lets you unlock 100 percent of the performance your power adder is capable of and do so safely.
No matter what kind of power adder you are (or will be) running, you need to consider the octane requirements of the fuel in relation to the horsepower gain from the power adder. In addition, you need to select plugs with a complementary heat range to maximize the performance of your combination. Both can take a bit of testing to determine.
As discussed in Chapter 1, if you use a power adder with your new EFI system, it’s important to purchase an EFI system that’s designed to work properly with it. Make certain that a particular manufacturer’s system works well with your power adder and contact them if necessary to verify this. Just because some guy on the Internet has been using a Brand-X EFI system with twin turbos doesn’t mean that you can too and not have problems in getting the vehicle tuned properly. Sure, it may be fine at WOT, but it may not be fine cruising around town . . . or vice versa. The most common power adders include nitrous oxide, boosted applications (such as centrifugal superchargers, Roots superchargers, twin-screw superchargers, and turbochargers), and water/ methanol injection.
This is the easiest of the power adders to manage. It’s also one of the only power adders that you can add to a high-compression naturally aspirated engine.
Shots less than 100 hp typically require only a few degrees less timing to prevent detonation. This is typically very simple to achieve but the ECU needs to have engine management to be compatible. In some cases, you can run a dry system (nitrous only) and the ECU can be set up to enrich the A/F mixture automatically. In other cases, you must run a wet system (nitrous and fuel), which adds the fuel manually to enrich the mixture.
There are two ways of interfacing a nitrous system to the ECU. The simplest method is connecting the ECU to an existing nitrous system so that the ECU knows when it is in use. This interface typically involves connecting the WOT switch that activates the nitrous to an input of the ECU. When the WOT switch is activated, the ECU reduces the timing accordingly.
If you’re a more hard-core nitrous user, you may elect to design a nitrous system that the ECU can manage. ECUs, such as the Holley Dominator (see Chapter 6 and Chapter 7 for more details), offer far more control.
They can do the following:
- Interface a master ON/OFF arm switch for the nitrous
- Progressively control the nitrous solenoids via PWM
- Control multiple stages of nitrous
- Automatically enrich the A/F mixture
- Govern activation by certain criteria (e.g., disabled when using a trans-brake)
When the arm switch is activated, all of the nitrous management is automatic. Also, the additional fuel required with the nitrous can be metered via the injectors, eliminating the expense and complexity of installing a wet nitrous system. Gone are the days of complex installations with multiple controllers and interfaces that must be set up and tuned separately (see Chapter 7 for more details).
Superchargers and turbochargers of any kind require an EFI system with engine management and boost compatibility. Regardless of which type of boosted application you run, you can safely and easily manage the timing when you’re in the boost. When using pump gas, it is necessary to reduce the engine timing proportionally to the amount of boost produced by the engine. It is also a good idea to remove timing as the charge temperature in the manifold increases. Both keep detonation at bay and allow your engine to live a long and healthy life. These are simple operations for the ECU to manage.
The obvious parts change is the MAP sensor, as the standard 1 bar sensor is for naturally aspirated combinations only. Here’s a guideline, depending on which sensor you have:
- 2bar:up to 14.7 psi ofboost
- 3 bar: up to 29.4 psi of boost
- 4 bar: up to 44.1 psi of boost
- 5 bar: up to 58.8 psi of boost
Centrifugal Superchargers:The supercharger is before the throttle body and blows through the throttle body. MAP is constant at all RPM and engine loads between the blower and the intake manifold. Timing and mixture enrichment are managed automatically via the timing and fuel tables.
Roots-Type Applications: There are two types of Roots-blown applications. Modern vehicles using Roots-style blowers have the injectors in the intake runners. The blower itself sits atop the intake manifold and creates boost when the engine is under load. No fuel passes through the blower. These installations often include intercoolers in the intake manifold to cool the charge.
On the other hand, muscle cars and hot rods typically use a draw-through application in which the fuel passes through the blower (which helps to cool the charge). The most common aftermarket EFI installations with Roots-blown draw-through applications use throttle bodies and injectors above the blower. When the engine is under load, the boost exists only in the intake manifold, which is under the blower. This requires a system designed specifically for such applications.
Some engine builders like to also include a set of injectors under the blower and in the individual runners of the manifold. This allows them to address the challenge of the blower pushing the fuel forward in the manifold, fine-tuning the cylinders to achieve the perfect mixture. This is exactly why the blower on a Top Fuel engine sits so far rearward (set back) on the manifold.
Turbochargers: Turbochargers are, for all practical purposes, just like centrifugal superchargers, as far as an EFI system is concerned. However, some EFI systems allow you to manage the wastegates electronically. If you’re a diehard turbo guy, this can be a huge help in tuning your combination.
This is one of the oldest power adders used in the internal combustion engine. In recent years it has gained momentum for several reasons. The quality of the fuel available at the pump is questionable at best for performance applications. It’s also inconsistent from one brand to another. Turbochargers and superchargers are more popular today than ever before. Both increase cylinder pressure when making boost and this necessitates higher-octane fuel to prevent detonation.
The objective is to increase the effective octane rating of the fuel. The unique thing about water/methanol injection is that it is compatible with naturally aspirated as well as boosted applications. When using it in naturally aspirated engines, you can increase the ignition timing in an effort to gain horsepower. When used in boosted applications, it isn’t necessary to retard the timing as much as the boost comes on and this can have significant effects on horsepower and torque.
Water methanol injection is also referred to as a liquid intercooler because it reduces the temperature of the charge before it enters the intake manifold (although not to the extent of nitrous oxide). As air is compressed its temperature increases, proving once again that there is no such thing as a free lunch. A side benefit of using water/methanol injection is that the combustion chambers are steam cleaned, so to speak, in the process of using it. With gasoline combinations it cleans the carbon deposits with regular use of your right foot.
Water/methanol injection is the least-expensive power adder and it’s easily managed. A wide range of kits is offered. They can be activated progressively via a MAP or MAF signal, allowing you to introduce the correct amount of the mixture based on actual engine requirements. At the time of this writing, the Holley HP and Dominator ECUs are the only units I’m aware of that allow you to manage water/methanol injection via the software, which is not only incredibly cool, but allows tuners to get the most from it.
Tuning with Power Adders
Tuning EFI systems with power adders is significantly simpler than tuning similar carbureted setups, but this is something better left to experienced tuners. Detonation is the enemy of all engines, but with power adders it can have immediate and devastating effects. In addition, any engine with a power adder is typically capable of serious horsepower. For these reasons, I recommend that an experienced tuner in a controlled environment perform this tuning. Most tuners also employ the use of a correctly calibrated knock sensor to prevent engine damage during the tuning process.
You should now know how to select the correct EFI system if you are using a power adder. As the EFI category in general is somewhat like the computer business, with new and improved software and hardware being introduced often, you’re well advised to consult directly with the manufacturer of a given system to review your specific needs to ensure a given system serves them.
After you’ve selected the system and it has been installed, you may elect to farm the tuning out to a shop equipped with a chassis dyno operated by an experienced tuner. I did. I prefer to work with tuners who tend to be a little conservative.
Both of my vehicles are fuel injected and both have superchargers. My daily driver, a 2003 Ford Mustang GT, has had a centrifugal supercharger and water/methanol injection on it for the past 70,000-plus miles and it runs as well today as it did the day it was tuned on the chassis dyno. My Olds (see Chapter 4) has an old-school Weiand 6-71 blower and 13,000 miles on the clock. Both are equipped with EFI and the tunes are maximized to provide the best performance and drivability with 91-octane fuel.
Written by Tony Candela and Posted with Permission of CarTechBooks