|
| |
|
| |
Buy with confidence!
If for any reason
you're not
completely satisfied
with an item, simply
return it within 7
days and the
purchase price will
be refunded.
|
|
|
|
| |
|
| |
We ship world wide.
All international
orders must be paid
online. Checks or
money orders drawn
on non-US banks will
not be accepted.
|
|
|
|
|
|
How Quadrajets Work
|
|
|
The first approach to working with most anything is to become familiar with how it works. With the
Quadrajet carburetor in particular, this is of the utmost importance. It is not only important to
understand the basics of carburetor function, but also how each system within the carburetor
works. The first step is to become familiar with the various parts of the carburetor, including the
different systems and components within them. Next, we must get a basic understanding of how fuel
and air flow through these systems over the range of engine operation. Armed with accurate
information, one can make the needed modifications for performance improvements with great
confidence.
|
|
|
 |
|
|
|
An 850cfm custom
Quadrajet gets ready to
feed the air/fuel to a stout
550 hp pump-gas street
engine on Kauffman Racing
Equipment’s dyno.
|
|
|
|
|
|
The Quadrajet, as with any other factory-delivered carburetor, was set up specifically for a single
application. The engineers designed and calibrated the entire vehicle, and each component,
including the carburetor, to work best within given parameters. In most cases only a correct
rebuilding is all that is needed to get the carburetor to work well in all areas, provided the engine
and all associated emission equipment are still in place and operational. However, we all know this
is quite rare. In the vast majority of cases, the well-meaning engine builder/tuner makes significant
changes to the engine in their quest for improved performance. Once one decides to employ a
non-factory intake, exhaust, and camshaft, or even to alter the engine’s static compression ratio,
we now become our own design engineer. The typical result is that all or most of the factory-
installed equipment is not up to the task of correctly supplying our engine with the ideal settings
over the entire engine speed and load range. Modifications to the different systems within the
carburetor now become mandatory if one is to extract the full performance potential from the
engine in all areas. This would be an easy task if the engine operated at a fixed speed and throttle
position, but they do not. Specific modifications to nearly every part of the carburetor are typically
required. The modifications outlined in this publication are for the most part easy to perform. The
hard part is to know where to perform them and why. Read on, because understanding the basic
systems can build confidence that your Quadrajet carburetor performs to expectations.
In order to fully understand carburetor operation, one must have a basic understanding of engine
function. During various driving situations, the engine operates over a rather broad revolution per
minute (RPM) range. The load placed on the engine also varies considerably. The carburetor is
asked to deliver the correct amounts of air and fuel in the correct ratio over the entire engine speed
and load range.
|
|
|
An engine is defined as a machine that converts heat into mechanical energy. An internal
combustion engine is nothing more than an air pump that uses a piston (or pistons) that moves up
and down within a cylinder or confined space. The constant up and down movement continually
increases and decreases the volume in the cylinder. This movement, combined with intake and
exhaust valves, creates the necessary processes that become the controlling forces of engine
operation. The vacuum created during the intake or downward stroke of the piston while the intake
valve is open causes air to be pulled into the cylinder. This air must pass through the carburetor
before entering the intake manifold. The duty of the carburetor is to ensure that the appropriate
amounts of fuel are present in the air at all times for sufficient combustion. As we go through the
various carburetor systems, one quickly sees that this is a tall order.
Theoretically, the perfect air-to-fuel ratio (A/F) for ideal combustion within the cylinder in pounds of
air to fuel is about 15:1. During normal engine operation, the air-to-fuel ratio, or A/F, varies from
about 20:1 to about 8:1. Economy ratios are typically in the 14:1 to 17:1 range and power mixtures
several ratios richer. At a glance, the task of the carburetor to deliver an ideal A/F of 15:1 seems
like an easy function to perform. One would think that all the engineer had to do was to set every
carburetor up with an exact calibration that would deliver the ideal A/F ratio. However, considering
the obstacles present during engine operation at various speeds and load, perfect conditions
seldom exist. There are always varying amounts of exhaust gases remaining in the cylinder(s)
during the intake stroke that dilute the intake charge. The air and fuel is seldom perfectly mixed as
it enters the cylinder, and the quality of the intake air can vary considerably. In addition, the intake
manifold does not deliver equal air/fuel mixtures to all cylinders. Also, changes in the fuel discharge
volume from the carburetor do not always result in equal changes in the mixture delivered to the
combustion chamber.
|
|
|
The dyno sheet shows back-to-back test runs from
a 455ci street engine on Kauffman Racing
Equipment dyno facility in Glenmont, Ohio. Part of
the testing included intake and carburetor changes.
A custom 850cfm 1976 Q-jet was used for the right
dyno chart, and a 1970 Ram Air Pontiac 750 CFM
carburetor on the left.
|
|
 |
|
|
|
|
|
Both carburetors were carefully calibrated for the dyno runs to make the results as accurate as
possible. (Kauffman Racing Equipment)
|
|
|
To further compound the problems, the engine builder often employs parts designed to increase
engine power, specifically a camshaft sporting larger specifications than the factory cam. The
longer overlap cycle (both valves open at the same time as the piston passes over top dead center
between the exhaust and intake strokes) further dilutes the combined air/fuel mixture that ends up
in the combustion space during the compression stroke. Without a proportional increase in the
static compression ratio of the engine, we now have an engine that is much more difficult to keep
running at low engine speeds. This results in uneven firing of the cylinders, low engine vacuum at
idle, and that “lope” from the exhaust pipes that many of us have come to love. Unfortunately, most
factory carburetors fall way short in being able to deliver the additional fuel required at low engine
speeds when the vacuum is relatively low. They simply weren’t calibrated for the new engine
parameters. We now have to either replace them with a carburetor that has more generous
capabilities or make specific modifications so that our existing carburetor is up to the task.
When outlining any carburetor modifications we must also consider that engines vary dramatically
in size or displacement. Displacement is usually listed as cubic inch displacement (CID), cubic
centimeters (CC), or liters. For comparison, a 400ci engine is approximately 6.6 liters or 6,600cc.
Engines not only vary dramatically in size, but also in compression ratio and power output. The
Pontiac division of General Motors, for example, delivered its basic engine block through the years
of production from 267ci to 455ci. The compression ratio of these engines could have been as low
as 7.7:1 to as high as 10.75:1, and the power produced from them varied from just less than 200 to
nearly 400 hp!
|
|
|
In early years, well before any significant emission standards were imposed, carburetors were often
matched very closely to the size of the engine and expected power potential. Carburetors are
typically rated in their ability to flow air in cubic feet per minute (CFM). There are various formulas
in place for determining the ideal CFM needed for any engine based on its displacement and RPM
potential. A “rough” racer’s formula is to simply double the CID of the engine. Although a crude
measurement, it has proven to be accurate enough for basic carburetor sizing. What we have seen
here from extensive engine dyno testing is that smaller carburetors can hurt peak power, but often
do not greatly affect overall vehicle performance. For example, we prepared a 455 Pontiac street
engine that made 485.9 hp topped with an 850 cfm carburetor. The engine made peak power at
5,100 rpm. According to one well-used formula (see chart) to determine the “ideal” CFM required
for this engine, the engine only needed about 644 cfm. Even so, a back-to-back pull was made with
a smaller 750 cfm carburetor and the engine made 16.6 less hp!
All carburetors operate on the basic principle of pressure difference. Any pressure less than
atmospheric pressure, or about 14.7 pounds per square inch (PSI), is considered a vacuum or low-
pressure area. By creating a vacuum or low-pressure area, it becomes possible to cause fluids and
air to move or flow from the high-pressure to the low-pressure area. To help increase the pressure
drop and improve fuel flow, carburetors use an hourglass-shaped restriction. This device is called a
“venturi.” Air coming down through the carburetor that encounters the venturi increases in velocity
as it passes the narrower area. This creates a low-pressure area and increases the “pull” from the
main fuel nozzle. Venturi is designed with a specific size, length, and curvature to be most effective
within the design parameters of the carburetor. One must consider that a small venturi increases air
velocity at any given CFM or airflow. This can be beneficial for precise fuel delivery and
atomization, but may restrict high-speed engine operation. A large venturi would be more
advantageous for high-speed engine operation, but is typically less effective at low engine speeds.
The production venturi size is usually a compromise to provide adequate low- and high-speed
engine operation. The Quadrajet uses a rather conservative primary side bore and venturi size to
be most effective at low and moderate engine speeds. It is complemented by huge secondaries for
sufficient airflow at high RPM.
|
|
|
The internal force that causes a pressure drop and movement of air into the internal combustion
engine is created by the downward movement of the piston during the intake stroke. The air that
enters the engine flows through the carburetor, then through the intake manifold and intake ports in
the cylinder head(s). Since the engine operates at various speeds and loads, the amount of air and
the pressure drop or vacuum created by the engine varies dramatically. This requires the
carburetor to have several different systems to ensure accurate fuel delivery over the engine
speed/load range.
The following pages take you through these systems on the Quadrajet carburetor. Understanding
the basic function helps us understand where, how, and why to make changes outlined in Chapter
6.
|
|
|
Formula for determining carburetor airflow requirements in Cubic Feet per Minute:
|
|
|
Street carburetor CFM = .85 x RPM x CID / 3456
Street/Strip carburetor CFM = RPM x CID / 3456
Racing carburetor CFM = 1.1 x RPM x CID / 3456
CFM = Cubic feet per minute
RPM = Engine revolutions per minute
3456 = Constant for conversion factors
.85, 1, and 1.1 = Approximate volumetric efficiencies for each type of engine
|
|
|
|
Previous | Next
|
|
|
|
|
|
|
|
|
|
|
|
This has been a sample page from
|
|
|
|
|
 |
|
How to Rebuild and Modify
Rochester Quadrajet Carburetors
by Cliff Ruggles
|
|
|
|
|
|
The Rochester Quadrajet carburetor was found perched atop the
engine of many classic GM and Ford performance vehicles. The
Q-Jet is a very capable, but often misunderstood carb. This book,
How to Rebuild and Modify Rochester Quadrajet Carburetors,
seeks to lift the veil of mystery surrounding the Q-Jet and show
owners how to tune and modify their carbs for maximum
performance. A complete guide to selecting, rebuilding, and
modifying the Q- Jet, aimed at both muscle car restorers and
racers. It includes a history of the Q-Jet, an explanation of how the
carb works, a guide to selecting and finding the right carb,
instructions on how to rebuild the carb, and extensive descriptions
of high-performance modifications that will help anyone with a
Q-Jet car crush the competition.
|
|
|
Click below to view sample
pages from each chapter
|
|
|
|
|
Chap. 1 - Quadrajet History
Chap. 2 - How Q-Jets Work
Chap. 3 - Carb Selection
Chap. 4 - Tools & Safety
Chap. 5 - Q-Jet Rebuilding
Chap. 6 - Performance Mods
Chap. 7 - Edelbrock Q-Jets
|
|
|
|
"Unlike some tech books you've probably seen, this one does a
good job on the photography, with all color photos shot with good
lighting, clear details, and clean backgrounds." -Musclecar
Enthusiast, October 2006, reviewed by Steve Statham
|
|
|
|
|
8-1/2 x 11"
Softbound
128 pages.
Approximately 300 color photos
Item: SA113
Price: $22.95
|
|
|
|
|
Click here to buy now!
|
|
|
|
|
|
|
|
This is a great book
anyone with a
Quadrajet will love!
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
| |
Other items you might be interested in
|
|
|
|
|
|
Holley - Rebuilding and Modifying
This unique book takes you step-by step through disassembly, parts
inspection, modification, reassembly, installation, and on-car tuning of
all popular Holley modular carburetors. This hands-on guide includes
clearly labeled steps, hundreds of detailed photos, and easy to
understand instructions that make working on Holleys as simple as
1-2-3.
|
|
|
 |
|
|
|
|
|
Price:
$18.95
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
How to Rebuild and Modify Carter/Edelbrock Carburetors
Author David Emanuel outlines carburetor types, gives a thorough look
at carb selection and carb function, and offers detailed information on
modifications, tuning, and rebuilding Carter/Edelbrock carburetors.
Also features the history of Carter as well as the history of the AFB
and the AVS since the purchase by Edelbrock. Contains more than
300 color photos, illustrations, and diagrams.
|
|
|
 |
|
|
Price:
$22.95
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Super Tuning and Modifying Holley Carburetors
Super Tuning and Modifying Holley Carburetors shows you how to
select, install, tune, and modify all popular Holley performance
carburetors. This book gives a detailed view of basic carburetor
functioning, modifying for performance applications, custom tuning for
street, racing, off-road, turbocharging, economy, and other special
uses.
|
|
|
 |
|
|
|
|
|
Price:
$18.95
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Shipping is combined and discounted for multiple item purchases!
Buy more and save on shipping!
We ship Worldwide! See International Shipping for more information!
|
|
|
Search Our Store for More Great Ford, Lincoln & Mercury Items!
|
|
|
FAST AND EFFICIENT SERVICE
We believe customer service and online retail can coexist. Our policy is to treat customers the way
we would like to be to treated. We strive to describe all items correctly. You have many options
online, but we believe our service is the best. We work around the clock to fill orders and ship items
within one business day. It is our goal to serve the customer before, during and after the checkout
process. Why gamble with your money and purchase from other sellers? We look forward to doing
business with you now and in the future.
|
|
|
FAST SHIPPING
Items usually ship within one business day of receipt of payment! We keep large quantities on hand
and have a state of the art inventory management system to ensure your items are in stock and
ready to ship.
|
|
|
YES, WE HAVE A RETURN POLICY
Satisfaction is guaranteed. Our store has a NO HASSLE RETURN POLICY within 7 days of
purchase. Your exchange will be processed upon receipt. If you are not satisfied with your
purchase, our knowledgeable team will do their best to make sure you get what you are looking for.
|
|
|
QUALITY AND AFFORDABILITY
Why pay retail when you can save money and benefit from our purchasing power? We stock large
quantities to get you the best prices and assure the item you order will be in stock and ready to
ship. We have a COMBINED SHIPPING incentive whereby each additional item adds $1.95 to the
s/h. The more you buy, the more you can save!
|
|
|
SHIPPING
Standard shipping is a flat rate of $4.95 to anywhere in the United States with USPS Media Mail.
Priority Mail shipping is available for an additional $3.00, or $7.95 shipping. Shipping is combined
and discounted for multiple items purchases as follows: first item regular price shipping, add $1.95
for each additional item.
INTERNATIONAL SHIPPING
We ship to Canada and Mexico with Priority Mail International for $10.95, and to most locations in
Europe, Australia, Asia, Japan and South America for $14.95. Shipping is combined and discounted
for multiple items purchases as follows: first item regular price shipping, add $1.95 for each
additional item. All international orders must be ordered and paid online, as we can no longer
accept checks or money orders drawn on non-US banks.
|
|
|
PAYMENT & SALES TAX
We accept Paypal, Visa, Mastercard, Checks and Money orders. Paypal is the preferred form of
payment. Our online shopping cart system is powered by PayPal, the most secure way to send
payment online. Iowa residents must add 7% sales tax.
|
|
|
If you have any questions or comments please feel free to contact us. We look forward to serving
you and fulfilling your needs.
|
|
|
Thanks for your business!
|
|
|
MRE
PO Box 47
Grinnell, IA 50112
|
|
|
|
|
|
|
|
