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4.6L / 5.4L Cylinder Heads
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Cylinder heads are a major contributing factor to power production on the 4.6L modular motor.
Since the 2-valve heads flow nowhere near as well as the 4-valve Cobras, it’s not surprising that
the 4-valve motors produced a great deal more power. The new 3-valve heads seem to be
positioned right between the two in terms of airflow, though the variable cam timing certainly
provides a benefit not realized by either the 2-valve or 4-valve motors. Since the modular motor
(like every engine) is nothing more than a giant air pump, the flow rate of the cylinder heads is one
of a number of factors that will determine the overall flow rate (we see as power) of the motor. The
more air the motor can process (in through the induction system and out the exhaust), the more
power it will ultimately produce. As with the intake manifold and exhaust system, bigger doesn’t
necessarily mean better when it comes to ports. In many cases, increasing the port volume can
increase absolute airflow, but (as always) there’s much more to the power equation than maximum
flow. Were maximum flow the key variable, we would hog out the port to the maximum available
dimension and watch the power grow. If only life were that easy.
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The 4.6L 2-valve motors really
respond to ported PI heads. We
installed these Stage 2 CNC-ported
heads from Total Engine Airflow (TEA)
on a 1998 (non-PI) short block and
were rewarded with nearly 90 hp.
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While peak-lift flow (measured at the maximum valve lift offered by the cams) is important, the
reality is that the valve spends more time running up to and away from maximum lift than it does at
maximum lift. Therefore, the flow rates throughout the valve lift curve are equally important. The low-
lift numbers are even more important on overhead cam motors, as the architecture generally does
not allow for high-lift values. This is especially true on the 4-valve motors, as the lift values even for
performance cams generally do not exceed .500 inch. The 2-valve motors attempt to make up for
their lackluster port design with higher lift (.550 to .600 inch), but when you only have .500 lift to
work with, you better make every effort to maximize the flow rates at all the lift values below that
point. After all, it’s the average airflow achieved throughout the lift range that produces the best
power curve. Lucky for us, the 4-valve configuration lends itself to impressive low-lift flow numbers.
While down on maximum available lift, the 4-valve heads also flow more at .500-inch lift than the 2-
valve heads do at .550-inch lift (or even .600). In fact, a ported set of 4-valve heads might outflow a
set of ported 2-valve heads by 80 to 100 cfm. All the extra lift in the world won’t make up that kind of
deficit.
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It’s too bad the aftermarket has not
embraced the 4.6L 2-valve motor,
as a set of TFS Twisted Wedge
heads for the 4.6L 2-valve would sell
like hot cakes. The only option for 2-
valve owners is to have the stock
heads ported like these Stage 3
heads from TEA.
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While most of the attention is paid to the flow rate through the ports, the reality is that the port flow
rate is only part of the power potential offered by the head. In Chapter 4, I’ll explain that the bank-to-
bank cam timing can be off dramatically. A related problem that can further skew the power output
(even on a stock motor) is the lifter (or lash adjuster) preload. Due to production tolerances in the
components, castings, and machining, the lifter preload can vary from .025 to .100 inch (or more).
Excessive lifter preload can actually push the valve off the seat, greatly reducing or eliminating
valve sealing in that cylinder. The reduced dynamic compression naturally causes a drop in power.
In addition to the lifter issue, the actual valve sealing from the production valve job can also hurt
cylinder pressure. Since both the valve job and valve length ultimately affect the installed height,
which in turn affects lifter preload, all of these variables are interrelated. Miss the valve job,
valvestem length, or lifter preload, and the power will suffer. Since a valve job (and possibly new
valves) is mandatory when performing head porting, care must be taken when it comes time to
reassemble the new components.
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Most enthusiasts opt to lower the static
compression when building a motor
specifically for supercharging or
turbocharging. The drop in
compression will allow higher boost
levels on pump gas, but it will decrease
off-boost efficiency, mileage, and
absolute power.
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In addition to cylinder head testing, this chapter also includes results on the effect of changes in
compression. The compression ratio will affect power, with higher compression offering more power,
but how much does the drop in compression hurt? Suppose you are in the market for a new short
block and want to add a blower down the line, or maybe you already have one on your existing
combination and you want to build (or buy) a dedicated forged short block to withstand the rigors of
boost. With your current 4.6L, the static compression is around 9.2:1 for a 2-valve or 10.0:1 for a
4-valve. Dropping the compression by a full point will result in a sizable change in power. Many
enthusiasts have built or bought a forged low-compression short block thinking that it will make
more power than their stock setup, but run at the same boost pressure, the low-compression motor
will most certainly make less power than before. Of course, the drop in compression may be
necessary to allow you to run safely on pump gas.
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Production 4-valve heads easily
outflow even a set of ported 2-valve
heads, but these F500 heads from
Ford Racing can really wake up a
4-valve Cobra motor.
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The guys at Accufab put the effect of compression to the ultimate test on an assembled 5.4L
4-valve motor. The benefit to the increased compression is actually greater when you add boost
into the equation, as the boost pressure becomes a multiplier. On the 5.4L motor, the increase in
static compression from 8.2:1 to 11.5:1 resulted in a gain of over 60 hp. Testing on the
supercharged versions of the same motors resulted in a gain of over 200 hp. Thus any gains
produced by the increase in compression ratio were multiplied by the pressure ratio supplied by the
blower. Therefore, every effort should be made to improve the power output of a naturally aspirated
motor, including increasing the compression ratio. This is especially true if you are building a motor
for a specific drag racing class that limits the size and/or speed of the blower or turbo. If the blower
or turbo is limited, you must do everything you can to maximize the power output at the
predetermined boost/impeller speed limit. Reducing the boost pressure at any given impeller speed
can increase the flow rate of the blower. This is accomplished by improving the power output of the
naturally aspirated combination.
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Previous | Next
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This has been a sample page from
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Building 4.6/5.4L Ford
Horsepower on the Dyno
by Richard Holdener
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The 4.6- and 5.4-liter modular Ford engines are finally
catching up with the legendary 5.0L in terms of aftermarket
support and performance parts availability. Having a lot of
parts to choose from is great for the enthusiast, but it can
also make it harder to figure out what parts and modifications
will work best. Building 4.6/5.4L Ford Horsepower on the
Dyno takes the guesswork out of modification and parts
selection by showing you the types of horsepower and torque
gains expected by each modification.
Author Richard Holdener uses over 340 photos and 185
back-to-back dyno graphs to show you which parts increase
horsepower and torque, and which parts don’t deliver on
their promises. Unlike sources that only give you peak
numbers and gains, Building 4.6/5.4L Ford Horsepower on
the Dyno includes complete before-and-after dyno graphs,
so you can see where in the RPM range these parts make
(or lose) the most horsepower and torque. Holdener covers
upgrades for 2-, 3-, and 4-valve modular engines, with
chapters on throttle bodies and inlet elbows, intake
manifolds, cylinder heads, camshafts, nitrous oxide,
supercharging, turbocharging, headers, exhaust systems,
and complete engine buildups.
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Click below to view sample pages
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Chap. 1 - Throttle Bodies
Chap. 2 - Intake Manifold
Chap. 3 - Cylinder Heads
Chap. 4 - Camshafts
Chap. 5 - Nitrous Oxide
Chap. 6 - SOHC Supercharging
Chap. 7 - DOHC Supercharging
Chap. 8 - Turbocharging
Chap. 9 - Engine Headers
Chap. 10 - 4.6 Engine Buildups
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8-1/2 x 11"
Sftbd.
208 pgs.
340+ b/w photos
Item # SA115P
Price: $22.95
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This is a great book and a
must have for anyone
considering modifying a 4.6 or
5.4 Ford for more power!
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Click here to buy now!
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How to Rebuild 4.6- and 5.4-Liter Ford Engines
The 4.6-liter can be built to produce any where from 300
hp up to 2,000 hp, and in turn, it has become a favorite
among rebuilders, racers, and high-performance
enthusiasts. How to
Rebuild 4.6-/5.4-Liter Ford Engines
expertly guides you through each step of rebuilding the
modular 4.6- and 5.4-liter engines, providing essential
information and insightful detail.
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Price:
$
22.95
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How to Build Performance 4.6 Liter Ford Engines
Sean Hyland gives you a comprehensive guide to building
and modifying Ford’s 2-, 3-, and 4-valve 4.6- and 5.4-liter
engines. You will learn everything from block selection and
crankshaft prep, to cylinder head and intake manifold
modifications. He also outlines eight recommended power
packages and provides you with a step-by-step buildup of a
naturally aspirated 405-horsepower Cobra engine. This is the
definitive guide to getting the most from your 4.6- and 5.4-liter
Ford.
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Price:
$
22.95
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Payment, Shipping & Sales
Tax: Iowa
residents must pay 7% sales tax. Items usually ship
within one
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