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Modifying Small Block Ford Cylinder Heads
Modifying Small
Block Ford Cylinder

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4.6-Liter Modular Engines
In 1996, Ford’s venerable 5.0L pushrod engine became a victim of tightening emission
requirements. The 4.6L modular V-8, first used in 1992 in the Crown Victoria sedan, became the
base engine in the Mustang GT. At 215 hp and 285 ft-lbs of torque, the base V-8 engine was
initially a disappointment to the Mustang enthusiasts weaned on the 5.0L and its prodigious low-
RPM torque. The Cobra engine arrived with 305 hp and 320 ft-lbs of torque, but again, the power
was much higher in the RPM band than the Mustang drivers were accustomed to. It took just a little
while (about a day for some) for the aficionados to realize that the modular engine was okay; it just
needed a higher axle ratio to best utilize the available power. A set of 4.10:1 gears absolutely
transforms a stock Cobra, and the lower-revving 2-valve GT worked well with 3.73:1. Once
everyone caught on that the 4.6L had to be wound out to near redline to really go, and a few of us
showed its potential, the naysayers were quiet.
Installing the Cylinder Head on a 4.6L Ford Mustang Engine 4.6L DOHC 1999 Ford Mustang Cobra Engine
Replacing the stock one-time-use head bolts and
main bolts on the 4.6 with aftermarket studs is a
good choice when rebuilding the engine.
This is the complete 320-hp 4.6L DOHC
engine as it came in 1999 and 2001 Cobras. It
features more traditional single intake ports,
unlike the 305-hp DOHC that came in
1996-1998 Cobras, which has two intake ports
per cylinder.
4.6L development escalated quickly after it became apparent that the 4-valve Cobra heads flowed
as much air in stock form as a really good set of aftermarket 5.0L heads. Bolting on a centrifugal
supercharger could boost the output of a stock Cobra engine from 305 to over 450 hp.
Unfortunately, we discovered early on that some of the components, specifically the rods and
pistons, weren’t up to the task of taking on more horsepower.

At the same time, we were developing better components, creating air-to-air intercoolers for the
supercharger kits, and gaining experience with improving the naturally aspirated 4.6 engines, first
for SCCA showroom stock racing, and then developing a 5.0L big bore version of the Cobra engine
beginning in 1997 for Motorola Cup endurance racing. In just over 2-1/2 years, from the time the
1996 Cobra came out, we were able to extract over 800 hp from the 4.6L 4-valve engine for drag
racing and 380 hp from the 5.0L road-race engine – using stock heads and intake! With the
potential of the 4.6L engines now clear for everyone to see, it wasn’t long before others joined the
fray. Although they were initially more expensive to work on, 4.6L engines established themselves
as being more cost effective in some respects. Where the stock 5.0L block was prone to failure at
over 600 hp, the production 4.6L iron block has been reliable at 900 hp, and the 4.6L aluminum
block is capable of 1,600 hp! No production North American V-8 block I am aware of is in this
league. Ford certainly over-engineered many aspects of the modular V-8 design. The overhead
cam valvetrain is capable of 9,600 rpm with very limited modifications. So, let’s see what we can do
with this package, shall we?
2-Valve 4.6L
Ford 4.6L Mustang Engine with Centrifugal Supercharger
Centrifugal superchargers have
been popular on the 4.6L
engines since the beginning.
Power increases of 40 to 60
percent are common on stock
engines. Higher power outputs
require improved rods and
The 2-valve 4.6L base engine for the Mustang GT arrived with 215 hp at 4,400 rpm, but its
restrictive cylinder heads ran out of breath at 5,000 rpm. This resulted in a narrow powerband
between 3,200 and 5,200 rpm where the engine really sang. Supercharging was the easiest way of
overcoming this deficiency for the first three years until better cylinder heads became economically
available. In 1998, Ford Racing released a high-performance 2-valve cylinder head, along with a
matching high-flow intake manifold (sometimes referred to as the SVO heads and intake). This
cylinder-head and intake-manifold combo is the best out-of-the-box package available today. With
an appropriate camshaft upgrade, this package provides an effective powerband from 3,500 to
6,500 rpm. The M-6049-D46 heads flow 203 cfm at .550 valve lift through the intake port and 141
cfm at .550 on the exhaust side. The intake valves are 46.83 mm, while the exhaust valves are
35.88 mm. To improve flow, the valve centerlines were moved 2 mm to unshroud the intake valve.
Combined with long-tube headers, underdrive pulleys, a cold-air inlet, and computer tuning, this
cylinder head/intake combo on a stock ’96-’98 short-block has produced over 350 hp on 91 octane
pump fuel – not too shabby for 281 cubic inches.
1999 Ford Mustang 4.6L 2 Valve Per Cylinder Engine with Power Improved Heads
In 1999, the 4.6L 2-valve
engine received the power
improved (PI) cylinder
heads and intake, plus
hotter cams, resulting in a
power jump to 260 hp.
In 1999, the Mustang GT was upgraded to 260 hp and 300 ft-lbs torque via Power Improved (PI)
cylinder heads, higher-lift cams, and a higher-flowing intake manifold. This upgrade substantially
improved the GT’s performance, and with the stock axle ratio upgraded to 3.27:1, the engine was
operating in its powerband more of the time. Immediately, the affordable price of the production PI
heads and intake allowed ’96-’98 GT owners to upgrade their cars to 1999 power levels. This is still
a very cost- effective ($1,500) upgrade, and also allows the owner a wider range of camshaft
choices, as many of the aftermarket designs are only available for the higher-lift PI heads. The PI
heads were redesigned to provide increased retainer-to-seal clearance, permitting higher camshaft

Going downstairs for a moment, two versions of the 4.6L iron block are available. The Romeo block
was used from 1996-1999. In 2000, due to capacity issues at the Romeo plant, some Mustangs
came with Windsor engines, including a different block, minor differences in the cylinder heads,
unique valve covers, and an eight-bolt crankshaft flange instead of the regular six-bolt crank flange
used on the Romeo engines. The Windsor plant normally produced the 4.6L and 5.4L engines
slated for duty in the F-series trucks, but due to overwhelming demand, it was tapped for extra
capacity. Functionally, the engines are interchangeable, as long as some of the unique exterior
dress is used, and we have built successful race and street engines using both blocks. The main
bearings are different between the two blocks, and this is probably the most significant thing to be
aware of when rebuilding these engines. The Windsor block has a “W” cast in the valley and on the
front of the block under the timing cover.
The 2001 Bullitt Mustang, which was based on the GT, came with a unique high-flow intake
manifold, similar in design to the Ford Racing performance intake, but manufactured to mate up
with the PI cylinder head intake ports. The Bullitt intake manifold added 5 hp and 15 ft-lbs of torque,
but it’s not significantly better than the production intake with an aftermarket throttle body and
plenum. One might be able to justify the cost on an all-out 2-valve engine.
Accufab 75-mm throttle body and intake elbow
Accufab 75-mm
throttle body and
intake elbow bolts
on an instant 11 hp.
Accufab’s John Mehovitz is a 4.6L pioneer and owner of the fastest 4.6L-powered drag car, which
runs the quarter-mile at 6.62 seconds at 210 mph. Mehovitz had produced a 75-mm throttle body
upgrade for the 4.6L 2-valve engine, but wouldn’t release it because it only produced a 2 hp gain
on a ’99 Mustang GT. After some investigation, he determined that the throttle body elbow was the
restriction in the inlet system, and with a new casting, gained a total of 11 hp on a stock PI engine
with the throttle body/elbow combo. The stock PI intake with an Accufab throttle body/elbow is quite
capable of producing 400 naturally aspirated horsepower – with ported cylinder heads, large
valves, camshafts, and long-tube headers.

Other bolt-on items that deserve mention include underdrive pulley kits, cold-air induction, and of
course, exhaust upgrades. Changing the original cat-back exhaust system is usually one of the first
modifications a Mustang owner makes, if not for the power increase, certainly to obtain a more
noticeable exhaust sound. Many excellent cat-back systems are on the market from companies
such as Magnaflow, JBA, and Borla.
Using a handheld programmer to adjust spark, fuel, and other engine parameters Ford 4.6 2 Valve Intake Manifold with NOS Nitrous Oxide Injection
Handheld programmers like this Diablo Predator
allow the owner to adjust spark, fuel, and many
other parameters in the engine-management
computer. This tool allows the owner to optimize the
calibration for all the modifications that have been
made to the car.
The NOS NOSzle system produces up to
300-hp gains on a prepared 4.6L 2-valve
engine. Of course, you can run a smaller
shot on a stock engine.
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This has been a sample page from

High Performance Mustang Builders Guide High-Performance Mustang Builder's Guide
by Sean Hyland
High-performance ‘94-‘04 Mustangs represent the high-water
mark for late- model Mustang enthusiasts. From the ’94-’95s with
the 5.0L, through the ‘96-‘04 models with the 2- and 4-valve 4.6
Ls, to the Bullitt, Mach 1, and factory supercharged ’03-‘04
Cobras – never before has such a range of highly modifiable
performance cars been available. These Mustangs were amazing
performers straight from the factory, but they can be even better
with the right combination of performance parts.
Regardless of which ’94-’04 Mustang you start with, the availability
of high- performance parts is unparalleled. You can build your
Mustang for drag racing, road racing, or improved street
performance – and High- Performance Mustang Builder’s Guide
1994-2004 will show you how! Author Sean Hyland uses over 300
photos to explain how to upgrade your Mustang’s engine,
suspension, chassis, transmission, rear end, brakes, and body.
There’s even a special chapter on getting active in various forms
of organized racing.

Sean Hyland is the proprietor of Sean Hyland Motorsport, which
builds and supports internationally competitive Mustangs for road
racing, drag racing, and everything in between. Sean recently did
a complete Mustang build-up for Speed Channel’s Sports Car
Revolution and is also the author of the bestselling title How to
Build Max-Performance 4.6-Liter Ford Engines.
Click below to view sample
pages from each chapter.
Chap. 1 - Chassis
Chap. 2 -
Wheels and Tires
Chap. 3 -
Chap. 4 -
Chap. 5 -
3.8 Engines
Chap. 6 -
4.6 Modular Engines
Chap. 7 -
Chap. 8 -
Rear Axles
Chap. 9 -
Chap. 10 -
Safety Equipment
Chap. 11 -
Get Involved!
Chap. 12 -
Project Cars
8-1/2 x 11"
144 pgs.
300+ B/W photos
Item: SA106P
Price: $
Click here to buy now!
This is a great book
that any Mustang
enthusiast will enjoy!

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How to Build Performance 4.6 Liter Ford Engines
Sean Hyland gives you a comprehensive guide to
building and modifying Fordís 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
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How to Build Performance 4.6 Liter Ford Engines
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Building 4.6 & 5.4 Ford Horsepower on the Dyno
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 donít deliver on their promises.
Building 4.6 & 5.4 Ford Horsepower on the Dyno
$ 28.95

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