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Tuning EFI For More Power
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The next step is the fun part: wide-open throttle. Many tuners jump straight to this part too early. It’s
easy to understand why. WOT is F-U-N when the engine makes a lot of power, and there is usually
some degree of glory associated with making a lot of power. If the previous steps have been
completed correctly, actual WOT testing should go rather quickly and smoothly for the calibrator. If
the PCM already has a very accurate model of fuel delivery and good representation of actual air
mass flow, striking the correct ratio with large flow numbers isn’t difficult at all. Spending more time
in the early stages of calibration to build an accurate model of airflow can reduce or eliminate the
guesswork needed to achieve the desired lambda at WOT. When this procedure is followed, actual
WOT calibration takes surprising little time.
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WOT testing on a chassis dyno
allows the calibrator to collect
large amounts of data for careful
review after each run. (Nate
Tovey)
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Conversely, tuners who fail to develop good mapping of actual engine performance at lower loads
often tend to take a long time to find the right combination at WOT. The quicker the proper settings
can be found at WOT, the less abuse the engine is subjected to during the testing process. Since
engines rarely fail at low load, it is advisable to make an effort to get the high-load tuning right in as
few attempts as possible. In short, if you have not already completed part throttle mapping, don’t
bother trying to tune the WOT maps. The calibrator who skips directly to WOT tuning without
mapping part load areas first almost certainly has a much more difficult time blending the maps later
for good drivability and transition to power.
The actual WOT tuning process is similar in concept to part load. The fuel delivery remains
consistent with the model used at medium and low loads. The airflow model must now be adjusted
in the upper range to match actual mass flow through the engine. Again, since the actual fuel
delivery is known, the assumption is made that any difference between the commanded lambda and
delivered lambda is a result of error in the airflow model. Just like at part load, this error is multiplied
by the predicted airflow to bring it in line with actual flow. An accurate, temperature-compensated
wideband oxygen sensor is absolutely necessary for accurate measurements during the WOT
tuning process. Standard HEGOs lack accuracy in the target lambda range for these tests and only
serve to mislead and confuse.
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The basic process for WOT tuning is
much like part throttle tuning. The
primary difference is that the target
A/F ratio is usually much richer than
stoichiometric. (Nate Tovey)
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A safe (lower than the expected maximum) amount of ignition timing is chosen and target lambda is
set to a slightly rich value. Running slightly rich and with less-than-ideal ignition advance to start
reduces the risk of detonation and helps keep exhaust gas temperatures safe. I usually use l ª 0.85
(12.5:1 a/f) for naturally aspirated engines and l ª 0.77 (11.3:1 a/f) for supercharged engines to
start. It is helpful to change large areas of the load maps for desired lambda to the target WOT
ratio at first. That way, even if calculated load at WOT is relatively low at low RPM, the target ratio
remains the same. This simplifies the math when correcting MAF or VE values to achieve the
desired ratio. Other fuel adders such as catalyst and piston protection strategies should be
disabled for this part of the testing. They can be reactivated after the completion of WOT airflow
mapping if needed.
For example, a naturally aspirated engine is desired to be run at l = 0.85 under WOT conditions.
First, all target lambda values in the fuel map are set to 0.85 for loads over 50%. The engine is
warmed to normal operating temperature and run in a WOT sweep from ~2,000 rpm to redline,
provided there are no signs of detonation or lean mixture. During this run, a datalogger is used to
record RPM, MAF, MAP, and actual lambda. If the engine achieves l = 0.85 at 2,500 rpm, no
change is necessary for those cells. If a lean condition of l = 0.9 is seen at 4,000 rpm, an
adjustment is calculated by dividing actual lambda by target lambda and using this as a multiplier
for the corresponding airflow value. If a mass air system is used, this number is multiplied by the
value in the MAF transfer function that was recorded at 4,000 rpm. If the value recorded by the
datalogger is 3.2 v at 4,000 rpm, the curve is adjusted locally by:
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Airflow correction = (0.9)/(0.85)
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This yields a ~6% correction to add to the airflow number in the MAF transfer function at
3.2v. Looking at the MAF transfer function, we might see a value of 30.0 lbs/min airflow at
3.2v. The airflow correction is applied to find the new airflow value to be entered into the
MAF transfer function in the PCM.
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New MAF value = (30.0lbs/min) x 1.058 ª 31.8 lbs/min
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The target air/fuel ratio is set to a
constant value in all areas where the
engine may operate during WOT. This
helps reduce the confusion associated
with trying to hit a moving target when
correcting the airflow model.
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Speed density applications simply point to a cell in the volumetric efficiency table at 4,000 rpm and
the corresponding MAP value (usually 95 to 100 kPa in this case) that can be adjusted by the same
1.058 multiplier. This process is repeated at all points where the delivered lambda varies from the
target by more than one or two percent. Within a couple pulls at WOT, this process should bring
the engine into almost exact desired fueling conditions.
The PCM likely rounds whatever new value you enter slightly to a step size allowed in its software,
so do not be alarmed if it is not exact. The point is to get the airflow model as close to reality as
possible. Most PCMs have small enough step sizes to get within 1% accuracy if you have the
precision and patience.
Once airflow has been accurately mapped all the way up, the true search for power can begin. New
target ratios can now be set in the PCM and verified on the dynamometer. The leaner the mixture,
the closer to the knock limit the engine gets. For forced induction applications, the line between
best power and detonation can be very thin. It is up to the calibrator to decide exactly how much
leaner he is confident in letting a certain engine operate. I typically aim for l ª 0.87 (12.7:1 a/f) for
naturally aspirated engines, l ª 0.78 (11.4:1 a/f) for positive displacement supercharged engines,
and l ª 0.80 (11.7:1 a/f) for centrifugally supercharged or turbocharged engines, but individual
cases vary.
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With the desired lambda reached, ignition timing can be added to find the best power without
knock. Two-degree increments usually work well to quickly find out if more timing helps. During
WOT testing, actual spark advance should be recorded as well as knock sensor signal, if available.
The OEM knock sensor can be a very useful tool in determining the maximum allowable advance
for an engine, and should be used whenever possible.
Most OEM knock routines are very accurate, just slow to recover. OEM knock strategies often
aggressively retard timing as soon as activity is detected from the knock sensor. For performance
applications, it can be beneficial to reduce the attack rate of knock retard as well as increase the
recovery rate that increments timing back to normal. Even though spark advance tries to return to
the desired value sooner, a repeat offense simply starts the routine over with another round of
spark retardation. By not changing the actual threshold, this technique preserves engine protection
while reducing the duration of knock strategy intrusion on the driving experience.
In some rare instances, the sensitivity of the OEM knock sensor may falsely trigger spark retard.
Changes to valvetrain components such as the addition of solid roller camshafts or an exhaust pipe
striking the vehicle body can transmit noises in the same frequency range as knock to the sensor.
Any interference issues should be mechanically fixed to allow normal operation, but valvetrain noise
issues may need to be accepted as a necessary evil. If false knock sensor input persists in the
absence of actual knock, the knock routine should be disabled. This can usually be done by setting
a maximum allowable authority for knock retard to zero degrees.
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Low amounts of spark advance at high engine speeds often lead to high exhaust gas temperatures
because part of the charge is often still burning when the exhaust valve opens. Increasing ignition
lead forces combustion to happen earlier inside the cylinder and reduces exhaust temperatures. If
exhaust gas temperatures are high enough to require advancing the timing, the knock threshold
may limit total advance. The solution is to richen the target lambda to reduce burn temperature and
allow the increased timing lead.
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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
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residents must pay 7% sales tax. Items usually ship
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