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Modifying Small Block Ford Cylinder Heads
Modifying Small
Block Ford Cylinder
Heads

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4.6L 2-Valve Cylinder Heads
When released into production, the 4.6-liter 2-valve arrived with 210 horsepower. In 1999,
changing the cylinder heads and the cams, the engine jumped up to 260 hp. We are going to look
at the heads available for the 4.6/5.4, and find the best ones to use for different activities.
‘92-‘98 Cylinder Heads
The ‘92-‘98 cylinder head as used on the Crown Victoria, Mustang GT, and F-150 truck, arrived
with a 51-cc combustion chamber, and a 146-cc intake port volume. The valve sizes were 44.5 mm
for the intake, and 34 mm for the exhaust. The intake port flows 156 cfm at .500 inches of valve lift,
and the exhaust reaches 116 cfm at .500 inches of valve lift. There is a wall in the combustion
chamber, adjacent to the intake valve, designed to promote in-cylinder mixture motion. As
delivered, this head made for a competent low-RPM engine, but it runs out of breath at 5000 rpm.
Although this is the lowest head on the food chain, if your engine came with it, you can still improve
what you have. This head has a few disadvantages in my opinion. One is the open-chamber design
has no quench pad to promote in-cylinder mixture motion. The other is that the wall used to
promote swirl impedes the intake flow. Oh yeah, and the exhaust port stalls at .350 valve lift, too.
The best things to improve this cylinder head involve some compromises.
1991 to 1998 non PI 4.6L 2 valve per cylinder head combustion chamber 1991 to 1998 non PI 4.6L 2 valve per cylinder head intake port 1991 to 1998 non PI 4.6L 2 valve per cylinder head exhaust port
This early 4.6 2-valve cylinder head shows the open combustion chamber with the wall beside the
intake valve to induce mixture motion in the chamber. The intake valve is 44.5 mm in diameter, and
the exhaust is 34 mm in diameter. The intake port has a round shape, with a teardrop to inject the
fuel into the port flow.
If you remove the wall in the chamber, flow goes up, but the chamber volume increases by 2 cc,
and you lose a bit in compression ratio. Once the wall is removed from the chamber, lay back the
chamber edge around both the intake and exhaust valves to the bore diameter of the block. This
will unshroud the valve as much as possible. It is possible to replace the stock valves with Ford
SVO valves or equivalent, or we can work with the stock valves. If the original valves are to be
used, a 30-degree back cut will improve the flow. Working with a carbide burr and cartridge roll, the
ports can be opened up to match the intake gasket dimension, and the exhaust flange contour on
the exhaust port. Once the ports are opened up, the seats can be cut on a valve seat machine. A
3-angle seat should be cut on both seats, and the results will be a 29-cfm improvement in flow on
the intake, and 20 cfm on the exhaust. I recommend a seat width of .060-.080 inch on the intake
seat, and .100 inch on the exhaust side.
1999-up Performance Improved (PI) Heads
In 1999, Ford released the Power Improved version of the 4.6 and 5.4. The shape of the intake port
changed substantially, so the intake was redesigned too, meaning the heads and intake both need
to be changed on an upgrade. The cylinder head flow was improved, and hotter cams were
provided to match. The PI head was a big step forward. The high-lift flow did not change
substantially, but the low and medium flow numbers were up 20-25% across the board. On the
exhaust side, the previous generation head quit working at .350 inches of valve lift, where the PI
head continues to improve right up to .600 inch. The improved torque and horsepower as a result
of the higher-lift cams and increased flow is hardly surprising. The shape of the valves was also
dramatically changed to improve flow; they now have a tulip shape when viewed from the side. The
combustion chamber gained a quench pad opposite the spark plug, and the volume fell to 42 cc.
This increased the compression, so a piston with a larger dish was used, but the static compression
ratio still increased to 9.7:1.
Ford 4.6 Liter PI 2 Valve Per Cylinder Head Combustion Chamber Ford 4.6 Liter PI 2 Valve Per Cylinder Head Intake Port Ford 4.6 Liter PI 2 Valve Per Cylinder Head Exhaust Port
The 4.6 Power-Improved (PI) cylinder head has a different shape to the combustion chamber, a
quench pad to induce mixture motion, and a new shape to the wall by the intake valve. The intake
valve diameter remains 44.5 mm, but the exhaust valve increases to 36 mm in diameter. The intake
port is more of a square shape with the injector stream integrated into the shape.
The intake port volume increased to 159 cc as well. These cylinder heads represent a bolt-on
power increase for early engines right out of the box. The corresponding intake manifold must be
used, as the gasket flange is unique, but this a very cost effective upgrade none the less. On
average, swapping over to PI heads and the matching intake will yield a gain of about 30 hp and 40
ft-lbs of torque. Improvements can be made on the PI head as well, if one were so inclined.

A number of shops now offer CNC porting on the PI heads. Just be cautious on purchasing heads
based on flow numbers. A 4.6 bore diameter is 3.551 standard, but many flow benches are set up
with 4.00-inch bores for older Windsor heads. This variance will skew the flow numbers higher than
they really are. Also, street heads can be ported too large, with the result being that velocity is lost.
I have seen PI heads that were taken out to the max, but on the street, they were terrible below
3500 rpm. The objective with street engines is to maintain good velocity while improving flow. Some
folks lose sight of this.
Race engines, on the other hand, operate in a fairly narrow RPM range, and can tolerate reduced
velocity in the ranges they will not operate. The race engine must be geared appropriately to exploit
the flow potential of a race-ported cylinder head. Another thing I see often is the valve guide
ground back to the port wall. Sure the flow will improve a bit, but you really cannot use a guide that
has been shortened like that. The valve requires a guide of sufficient length to provide adequate
support. Without that support, the valve seal will go away quickly and power will be lost. We have
even tried to lengthen the guide to provide more support to the valve. The 4.6 has a longer portion
of the valve stem above the retainer than most, and maintaining some motion control on the valve
stem is important to the overall performance of the engine.
Ford SVO Cylinder Head
In 1998, Ford released the SVO 2-valve head, which is the best 2-valve head produced to date.
This head has a 51-cc combustion chamber like the early production head, but that is where the
similarity ends. The chamber does not have the wall near the inlet valve, relying instead on a
quench pad opposite the spark plug to create in cylinder motion. The valve centerlines have
been moved .080 inch closer to the center of the bore, unshrouding the oversized valves. The
intake valve measures 46.8 mm, and the exhaust valve measures 35.8 mm. The intake port
runner volume is 173 cc, the largest of the three 2-valve heads. All these attributes combine to
produce 206 cfm at .600-inches of valve lift on the intake side, and 142 cfm at .600 inch on the
exhaust side. Even more impressive is the fact that the SVO head outflows both other heads at
every data point, so it is not just a high-flow head up top, but also throughout the rest of the RPM
range.
SVO Ford 4.6 Liter 2 Valve Per Cylinder Head Combustion Chamber SVO Ford 4.6 Liter 2 Valve Per Cylinder Head Intake Port SVO Ford 4.6 Liter 2 Valve Per Cylinder Head Exhaust Port
The SVO cylinder head has a quench pad opposite the spark plug, and unlike the production
heads, has no wall by the intake valve to promote mixture motion. The valve sizes are enlarged to
46.83 mm on the intake valve, and 35.88 mm on the exhaust. The intake port is still a round shape,
but with the injector spray path more widely integrated than the early production head.
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This has been a sample page from

How to Build Max Performance 4.6 Liter Ford Engines How To Build Max Performance 4.6 Liter
Ford Engines
by Sean Hyland
This revised edition features new and current
information throughout the text, an additional 16 pages,
and all black and white photography.
When the ’96 Mustang came out with the 4.6-liter V-8, some
performance enthusiasts were scared away by its technology. But
those days are long gone. Ford added horsepower and torque to
its 2- and 4-valve V-8s over the years, and the number and
quality of available aftermarket performance parts has exploded.
Ford took things to the next level with the new 3-valve Mustang
GT engine and the 5.4-liter GT and Shelby GT500, adding even
more high-performance options.

In this updated edition of How To Build Max-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.

In Stock and Ready to Ship!

Click below to view sample
pages from each chapter.
Chap. 1 - Engine Block
Chap. 2 - Crankshafts
Chap. 3 - Rods
Chap. 4 - 4.6 Pistons
Chap. 5 - Cylinder Heads
Chap. 6 - Int. Manifolds
Chap. 7 - Fuel Injection
Chap. 8 - 4.6 Camshafts
Chap. 9 - 4.6 Exhaust
Chap. 10 - Ignition
Chap. 11 - Lubrication
Chap. 12 - Cooling
Chap. 13 - Power Adders
Chap. 14 - Packages
Chap. 15 - 405HP Engine
Softbound
8-1/2 x 11
1
44 pages
445 B/W Photos
Item #SA82P
Price: $22.95
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This is a great book that any modular engine owner or enthusiast will enjoy!

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