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The Basics of Fuel Injection
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Before we delve into the finer points of EFI table adjustments, let’s take a step or two back and
understand exactly what is happening under the hood. It has been said before and it is reinforced
here again: An engine is little more than an air pump. It just so happens to be that with the right mix
of ingredients, we get to harvest a little hidden energy on the way through. Both the air we breathe
and the gasoline in the tank are made up of complex combinations of chemicals with all kinds of
hidden potential. However, this reaction can only take place between certain amounts of each
chemical. Just like a baker knows that too much flour turns cookies into biscuits, too much fuel gives
us a less-than-ideal reaction.
Ideally, to have no extra molecules of either oxygen or fuel left over at the end of the reaction, we
must start with the right ratio of components. Chemists call this correct ratio a stoichiometric mix.
For gasoline and air, it is 14.68 pounds of air for every pound of gasoline. Notice that we say
pounds of air and not cubic feet. On a molecular level, each string of octane and each oxygen
molecule have a specific mass. To get the right ratio of strings of octane to oxygen molecules, we
must calculate based on mass. Changes in barometric pressure, manifold pressure, and
temperature have a significant impact on the density of air and fuel, so we must remember that one
cubic foot of air does not always contain the same number of oxygen molecules. Once again, this is
where electronic fuel injection shines with its ability to compensate for such changes almost
instantaneously.
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The air you are breathing right now
is not pure oxygen. The primary
component is actually nitrogen, with
only about 23% oxygen. This is why
the engine must consume more total
air mass to obtain the oxygen
required to react with the gasoline.
(Nate Tovey)
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4 Cycles of an Engine
“Suck, Crush, Bang, Blow,” or at least that’s how I remembered it in college. Maybe “Intake,
Compression, Power, Exhaust” is less offensive, but I doubt it leaves as much of an impression on
the mind.
The process begins with a relatively empty space inside the cylinder of the engine and an open
intake valve. As the piston moves down, pressure inside the cylinder drops below that of the intake
tract and atmosphere. This pressure difference is what pushes the air and fuel into the chamber.
Since we know that each ounce of fuel only carries so much energy and must be mixed with an
appropriate amount of air to burn, the more total mix that can find its way in to the cylinder each
time the valve opens, the more potential we have to make power.
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Datalogging of the engine sensor data
during a wide open throttle run reveals
the actual air consumption. This air
consumption is used by the PCM to
calculate engine load. Notice how this
naturally aspirated engine develops
approximately 86% engine load at
WOT.
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Obviously there are ways to increase or decrease the amount of charge filling the cylinder each
time. The most obvious method of charge fill control is the throttle blade. By closing off a portion of
the inlet tract with a blade, the amount of air available for the next intake stroke is reduced. Mixing a
smaller amount of intake air with a smaller amount of fuel yields a smaller power potential, but also
resists the tendency of the engine to pick up speed. Conversely, with a throttle blade completely
open, the amount of air entering the cylinder can be increased by taking advantage of standing
waves in tuned length runners, leaving the valve open longer with changed cam timing events, or
changing the pressure differential severely with supercharging.
Actual charge fill is an indicator of how much work the engine is doing at the moment. The more
charge filling the cylinders, the harder the engine is working. This work is expressed in terms of
“load” or “Volumetric Efficiency (VE).” Load and volumetric efficiency are just two methods used to
describe the actual mass of airflow through an engine compared to the theoretical mass flow based
on its displacement and speed. The theoretical amount of charge fill is the mass of air that would
occupy the same volume as the engine displaces. This mass is found by multiplying volume and
normal atmospheric density.
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M air,engine = (Vengine) x (rair)
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The theoretical filling is calculated at standard temperature and pressure (STP or STD) where
density (rair) is equal to 0.00004671 lbm/in3. To find the flow rate, we normalize for the number of
complete displacements over time. A four-stroke engine has two revolutions per cycle of
displacement, so the displacement rate is one-half of actual engine speed. The theoretical airflow
rate of an engine is:
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M = (Vengine) x (rair) x (RPM/2)
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The theoretical 100% filling of a four-stroke engine with a 300 cubic inch displacement operating at
1000 rpm is calculated by:
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(300 in3) x
(0.00004671 lbm/in3)
x (1000 rpm)
__________________
2
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= 7.01 lb/min air mass flow through engine
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This engine would theoretically move 7.01 pounds per minute of air through itself at standard
ambient conditions and 1,000 rpm. By closing the throttle blade to reduce airflow and horsepower,
the engine is only allowed to move 1.40 pounds per minute. The ratio of actual instantaneous mass
flow to theoretical pumping gives us volumetric efficiency or load.
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This means that the reduced throttle position yields a volumetric efficiency of 20%. Typical engine
loads can vary from 10 to 18% at idle. Most steady cruising at street and highway speeds happens
at approximately 20 to 30% load. Light acceleration is usually between 30% and 60% engine load.
Wide-open throttle operation for naturally aspirated engines results in a load anywhere from 60% to
105%, depending on how efficient the intake, camshaft, and cylinder designs are. Supercharged
engines routinely see loads in excess of 100% once boost is present in the manifold. For reference,
most 5.0L Ford Mustang engines show approximately 80% load at peak power. With a Vortech
centrifugal supercharger making 8 psi of manifold boost, the same engine can show approximately
140% load at peak power.
EFI systems excel by being able to accurately calculate engine load at any time. Load has a large
impact on what the engine wants for operating parameters to perform optimally. As load increases,
spark advance typically has to be reduced to prevent knock. At high loads, fuel enrichment may
also be necessary to control exhaust gas and component temperatures.
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Any way you slice it, just pumping air from the outside world into the cylinder takes some amount of
energy. The engine needs to come up with some power to drive this process somewhere. Once a
mix of air and fuel has found its way into the cylinder, we need to find a way to do something with it.
The piston moving up in the bore with both valves closed does two things very effectively. First, it
compresses the mixture, giving it a new set of properties. A denser air/fuel mix tends to put all of the
molecules in much closer proximity, making for a faster reaction once things start to happen. Also,
Boyle’s Gas Law tells us that as the volume decreases, pressure and temperature increase.
PV=nRT, remember? A hotter, denser mix makes for a faster reaction. Just like the intake stroke,
compressing this mixture takes energy to drive the piston up against a mixture that generally doesn’
t want to get any smaller on its own. This energy needs to come from somewhere too.
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An early form of fuel injection is
central port injection. Seen here, the
injectors are mounted in the middle
of the intake manifold on what
essentially looks and acts like an
electronic carburetor. (Nate Tovey)
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Previous | Next
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This has been a sample page from
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Engine Management: Advanced Tuning
by Greg Banish
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As tools for tuning modern engines have become more powerful
and sophisticated in recent years, the need for in-depth
knowledge of engine management systems and tuning techniques
has grown. Tuning engines can be a mysterious art, as all
engines need a precise balance of fuel, air, and timing in order to
reach their true performance potential.
Engine Management: Advanced Tuning explains how the EFI
system determines engine operation and how the calibrator can
change the controlling parameters to optimize actual engine
performance. This book takes engine-tuning techniques to the
next level. It is a must-have for tuners and calibrators and a
valuable resource for anyone who wants to make horsepower with
a fuel-injected, electronically controlled engine.
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Click below to view sample
pages from each chapter
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Author Greg Banish is a calibration engineer with extensive
aftermarket performance calibration experience. With over a
thousand unique calibrations performed over five years, he has
worked with enthusiasts and OEMs alike to improve the
performance and driving behavior of a wide range of vehicles.
The book contains detailed equations, graphs, and illustrations.
Also included are valuable and practical examples, including real-
world examples based upon the author’s experience that will help
more advanced readers apply this new information to situations
that are commonly seen during calibration.
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1 - Introduction to EFI
2 - Basics of Fuel Injection
3 - Carbureted Engines
4 - EFI System Inputs
5 - Fuel Injectors
6 - EFI System Fuel Control
7 - Ignition Systems with EFI
8 - Data Logging
9 - EFI System Calibration
10 - Idle Calibration
11 - Tuning for More Power
12 - Fine Tuning EFI
13 - Tuning EFI with Blowers
14 - Tuning Ford EFI Systems
15 - Aftermarket EFI Systems
16 - INCA OEM Calibration
17 - External EFI Controllers
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8-1/2 x 11"
Soft bound
128 pages
200 color photos
Item # SA135
Price: $22.95
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Click here to buy now!
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How To Build High-Performance Ignition Systems
The complete guide to understanding automotive ignition systems.
Covers components, systems & subsystems for street & race
applications. This book will help you understand how your car’s ignition
works, and it will help you choose the right components for your car’s
performance needs, whether it’s a 1965 289 or a 2003 Cobra with a
4.6-liter modular motor.
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Price:
$22.95
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How to Tune and Modify Engine Management Systems
Drawing on a wealth of knowledge and experience and a
background of more than 1,000 magazine articles on the
subject, engine control expert Jeff Hartman explains everything
from the basics of engine management to the building of
complicated project cars. This book is updated to address the
incredible developments in automotive fuel injection technology
from the past decade, including the multitude of import cars that
are the subject of so much hot rodding today. Hartmans text is
extremely detailed and logically arranged to help readers better
understand this complex topic.
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Price:
$27.95 |
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Turbo High Performance Turbocharger Systems
This book is the most detailed and up-to-date resource on
turbocharging. You'll learn how turbochargers work, how to
choose the right turbo or turbos for your engine by reading
flow maps, and how to tune your engine to run perfectly with
your turbo system. Uses more than 300 photos and technical
information to help you make more horsepower. It also
discusses the various components of a turbocharger and
explains how to decode turbocharger model numbers,
compressor maps, other specifications and includes a
complete step-by-step turbocharger tear-down and rebuild.
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Price:
$22.95
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Turbochargers
How to select and install the correct turbo for big or small
horsepower gains. Discusses turbocharger design, sizing,
matching, controls, carburetion, exhaust, ignition,
intercooling, marine and high altitude applications. The most
comprehensive book available. Turbo suppliers and kit
maker addresses are included. “Everything you could possibly
need to know about turbochargers for automotive applications
is in this book.
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Price:
$18.95
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Payment, Shipping & Sales
Tax: Iowa
residents must pay 7% sales tax. Items usually ship
within one
business day of receipt of payment! Standard shipping is a flat rate of
$4.95 to
anywhere in the United States with USPS Media Mail.
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POLICY
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