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Tuning EFI with Blowers
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So far, the focus of this book has been naturally aspirated engine calibration. Although forced
induction has been occasionally mentioned, it deserves some more focused attention. The
aftermarket performance industry is flush with ways to add power to an engine. Few of these
methods come close to the potential that forced induction offers for power increases. Many OEM
vehicles are built with superchargers or turbochargers from the factory, which often leaves the door
open for the enthusiast to simply increase the pressure ratio in the search for power. At the end of
the day, the concerns are the same. Any time more compression happens to a gas, its temperature
rises by some amount. How much temperature increase comes along with the compression is a
direct result of the amount of compression happening and the efficiency with which it is being done.
Not all compression methods are created equal.
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The Ford Lightning is an example of a
vehicle that came from the factory with
some form of supercharging. The ECU
has logic that can accurately calculate
engine loads in excess of 100%. (Nate
Tovey)
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It is important not to confuse manifold pressure with cylinder pressure. The two are linked, but the
relationship between them is unique for each engine combination. Cylinder pressure is the primary
deciding factor when considering how much less timing is needed under boost compared to the
same engine under atmospheric conditions. Looking at load instead of boost gives a better
representation of what the engine wants. Increases in airflow cause load shifts, not boost. Boost is
just a measure of restriction between the engine and compressor. If exhaust backpressure or
camshaft design is changed to increase flow, boost may actually decrease (without a change in
drive/pulley ratio) while airflow and load increase. This condition may require a reduction in timing
to prevent knock at the higher load even though boost has been reduced. The only way to know for
sure is to test under load.
As mentioned before, extra fueling is used to improve combustion stability and reduce temperatures
under high load. The increase in available airflow may also require revision to acceleration
enrichment requirements to accommodate the higher instantaneous increases in airflow on tip-in.
Supercharged engines should still be able to operate normally at low and mid load. The addition of
forced induction alone does not require that the engine always be operated rich. The normal
procedure for part throttle mapping remains and l = 1 fueling for most operating conditions should
still be targeted to preserve fuel economy and emissions.
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Part load spark calibration is again almost identical to that of a naturally aspirated engine. MBT is
not affected by the supercharger at part throttle. MBT remains the ignition target at part load.
There will just have to be a blending into the new higher load regions of the map.
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Centrifugal Superchargers
Probably the most widely used compressor in the performance aftermarket is the centrifugal pump.
Companies such as Vortech, Paxton, and ATI produce countless systems for almost every
performance vehicle on the market. These compressors are driven by the accessory drive belt,
linking their impeller speed directly to engine speed. Because these compressors offer little
increase in flow at low speeds, they are overdriven through both pulley ratio and internal gear sets.
Still, the centrifugal pump design requires relatively high speed to reach its potential. Actual engine
boost output from a centrifugal supercharger increases with engine speed. Drive losses for a
centrifugal supercharger also vary depending on the load. At idle they only require a few
horsepower to turn, but losses increase with speed. A typical aftermarket street supercharger can
take anywhere from 30 to 50 hp to drive at full load. This is very real power that must be transferred
from the crankshaft to the supercharger, and it must be taken into account when calculating fuel
system requirements. Luckily, the drastic increase in airflow more than outweighs the parasitic
losses at high load.
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This engine is equipped with a Paxton
centrifugal supercharger. A longer
accessory drive belt is used to
accommodate the extra pulleys and
positioning. (Nate Tovey)
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As impeller speed increases, so does pumping volume and efficiency… to a point. The result is
usually a wide-open throttle boost curve that increases almost linearly with engine speed. At low
RPM, there is almost no added manifold pressure. Therefore, engine calibration at these speeds
can be done with a leaner lambda and more aggressive spark advance below peak camshaft
efficiency, just like on a naturally aspirated engine.
Even with relatively little increase in engine load at low throttle position, air is still being pumped by
the compressor at low speed. This pumping volume is still greater than the engine’s airflow
requirements at idle and low load, so pressure builds between the throttle blade and compressor.
The added pressure on the compressor blades creates drag on the accessory drive that can make
idle control difficult. A bypass valve is used to divert this pressure back to the inlet side of the
compressor. The valve is actuated by a vacuum diaphragm connected to the intake manifold. When
the throttle is opened and manifold vacuum disappears, the bypass valve closes and forces all
compressor output to be routed directly into the engine.
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Engines equipped with centrifugal
superchargers make peak boost at
redline. The exponential response
generates most additional loading after
the engine passes peak torque. (Nate
Tovey)
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One word of caution for mass airflow based systems is to ensure that all flow only passes the
metering element once. It is a common mistake to route bypass air back into the inlet upstream of
the MAF sensor, causing double metering during bypass. This makes proper MAF calibration all but
impossible. Likewise, if the bypass is placed after the MAF element, it must not vent to atmosphere.
Dumping metered air back to the atmosphere results in a rich condition as the PCM assumes all
metered air is actually going into the engine.
As engine speeds increase, boost pressure at WOT also increases, resulting in loads exceeding
100%. Load continues to increase all the way until redline unless otherwise restricted. Unless the
drive belt slips, centrifugal superchargers develop maximum boost at redline. Cylinder pressures
should steadily increase with speed as well, with moderate increases near peak torque and
substantial improvements at high speed where the efficiency of the centrifugal pump becomes
greater.
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Because of the variable load increase, a centrifugal supercharger system rated to deliver 10 psi
(0.7 bar) of boost only does so at maximum speed. If this maximum speed is 6,500 rpm, there may
only be 5 psi (0.35 bar) of boost present at the torque peak near 4,500 rpm. This tells us two
things. First, engine load increase near peak torque (the point at which cylinder pressure would
normally be highest) is significantly less than what is seen at redline. This means that less timing
retard is necessary at this point in order to maintain good engine durability and knock resistance
versus redline. Secondly, increasing loading means that the high-RPM pumping efficiency of the
newly supercharged engine system is extended. An engine that would otherwise lose volumetric
efficiency near 6,000 rpm may now continue to develop useful power to 6,500 rpm or higher.
This is due to the ever-increasing manifold pressure overcoming the loss of ram tuning
effectiveness. When peak load is reached at high engine speed, more timing must be pulled to
avoid knock. The increased inlet temperature that comes with boost should be compensated for in
the calibration. This is done by adjusting the IAT timing function accordingly to pull timing at high
temperatures. For this reason, the IAT sensor should be placed such that it always measures
actual manifold air temperatures in supercharged applications.
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This supercharged engine makes over
1,700 hp and an appropriately large
amount of boost. To vent this
tremendous pressure when the throttle
is closed, two bypass valves are
employed to reduce the load on the
compressor wheel. (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
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America for
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POLICY
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