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Modifying Small Block Ford Cylinder Heads
Modifying Small
Block Ford Cylinder

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Improving The Performance of Ford Small Block Cylinder Heads
Article by Mark Reams, ASE Certified Master Automotive Technician, ASE Master Engine Machinist
The Ford small block Windsor engine has been the performance engine of choice for many Ford
enthusiasts over the years. One of the most important factors for producing power with any engine is the
cylinder heads. While there is an abundance of after-market cylinder head choices for the Windsor
family of engines, many do-it-yourselfers will choose to use original cast iron offerings for originality or to
cut costs. In this article we’ll discuss the Windsor cast iron cylinder heads, valve size and port shape,
and how to improve the performance of these castings.
There have been a few different valve sizes used over the years on this family of engines, but typically
most intake valves are 1.78-inch and exhaust measure 1.45-inch. Port flows vary with different castings
as well, but typically measure around 150 CFM on the intake port at 0.500-inch lift and 100 CFM at
0.500-inch lift on the exhaust port. These flow numbers may work great for a car that is driven to the
grocery store occasionally and rarely sees 3000 RPM, but they’re low for a performance engine
1965 289 combustion chamber and valves fitted with oversized valves One of the easiest low budget tricks to
improve the performance of the 289, 302
and 351W head is to fit it with Chevrolet
1.94-inch intake and 1.6-inch exhaust
valves. The 1.94-inch intake was the
standard small block Chevy intake valve
and can be purchased new or found used
in salvage yard casting or from a variety
of sources. While many may scoff at the
thought of using used intake valves in a
performance engine, thousands of
engines have been rebuild without
replacing the intake valves and there’s no
reason used intake valves from a small
block Chevrolet can’t be ground and
refinished and installed into a Ford
cylinder head, especially when working on
a budget. This is the normal rebuild
procedure in many racing classes with
where the motors can be claimed.
This 1965 289 head has been fitted with 1.94-inch
intake and a 1.6-inch Chevrolet valves. Notice that
theres barely enough room for a fingernail between the
two valves. This is about the largest valves that can be
used in production heads. Also notice the small chamber
size on this head. Heads after 1974 have considerably
larger chambers that extend considerably past the spark
Typically the cast iron seats in the cylinder heads are enlarged and cut to the correct size for the new
valves with valve grinding equipment. This usually brings up the point that Ford cylinder heads used
induction hardened valve seats and quite a bit of material has to be removed to install a 0.160-inch
bigger intake and a 0.150-inch bigger exhaust valve. Technically the correct procedure would be to
install new hardened valve seats along with the new valves to prevent rapid seat wear. Installing valve
seats can be an expensive procedure and often it’s beyond the price cap of many engine rebuilds. My
personal opinion on this is based on experience, and I know of countless engines rebuilt using the
original cast iron seats cut to larger sizes, many with over a hundred thousand miles on them, and I have
yet to see a valve seat fail.
Something that should be considered is the year of the cylinder head castings and the combustion
chamber size. There are quite a few books out there that list combustion chamber size for Ford cylinder
heads, but a good rule of thumb is that Ford used fairly small chambers through 1973 and larger
chambers after that. As compression ratios were be lowered in the late 1960s Ford used dished pistons
to lower the compression ratio rather than larger chambers in the heads. After 1973 most engines
began using pistons that were more of a flat top design and combustion chamber sizes were enlarged
considerably to reduce the compression ratio.
While any cylinder head from before 1974 is a good choice to provide a slightly raised compression ratio
for a performance street engine, my personal favorite would be the 1965 289 cylinder head. They have
a fairly small chamber volume that provides a nice compression ration for a well-tuned 302 with flat top
pistons, but there are several other advantages as well. In mid year 1966 Ford changed to rail rocker
arms on its small block cylinder heads. The push rod holes on Windsor cylinder heads were opened up
into large round holes and cast iron rocker arms with a lip on each side were installed to keep the valve
train in alignment. A different rocker arm stud and nut was also installed that was no longer adjustable.
Prior to 1966 cylinder heads had guide plates cast into the cylinder heads and used an adjustable stud
and nut with the rocker arm allowing for valvetrain adjustments. While valve train adjustment isn’t
absolutely required it is a nice feature for a performance cylinder head and a necessity with a solid lifter
camshaft or if the cylinder heads have been milled or the cylinder block decked.
Push rod guide holes in a 1965 289 head The ports in production cast iron heads were fairly
restrictive, especially the exhaust port. There was a
large hump cast into the middle of the exhaust port on
most head castings that was drilled on many cylinder
heads to allow air to be pumped directly into the
exhaust port to improve emissions on these engines.
On a performance rebuild typically a die grinder is
used to remove this hump for the exhaust port and
improve flow. On more serious applications it’s not
uncommon to remove the hump and part of the valve
guide pedestal and port roof from the exhaust port to
open it up in this area and produce more of a straight
shot from the back of the exhaust seat bowl area to
the port opening at the header.
In this picture of a 1965 289 head you can see
the push rod slots cast into the cylinder heads.
This head also has adjustable rocker arms.
The studs are pressed into the head as only
the 289 HiPo had screw in studs.
Cylinder head casting numbers
The year of the cylinder head is usually easily identified. Early heads had the engine size and the model
year cast into the bottom side of the head along the intake ports. Shown here is a 1965 289 head. Later
heads usually still have the engine size, but not the year. On later heads the casting number will usually
identify the year. The C5AE shown to the right in this picture indicates 1965. C6AE would indicate 1966,
C7AE would indicate 1967 and so on. D0AE would indicate 1970, D1AE would indicate 1971 and on and
on. B was used to start casting numbers of parts from the 1950s, E for the 1980s, and F for the 1990s.
Exhaust port view of a small block cylinder head Exhaust port viewed from combustion chamber side
This image shows the large hump in the middle of
the exhaust port in a 302 cylinder head. On some
engines these had a hole drilled in them and
were used to pump air directly into the exhaust
port to improve emissions.
This picture shows the same hump in the
exhaust port through the valve seat opening.
This hump is usually removed with a die
grinder for performance applications. You can
also see the sharp edge on the right side of
the valve bowl area. These are usually
smoothed up with a die grinder to improve flow.
Cutaway of a cylinder head showing the exhaust port
This cutaway of a 1973 302 head shows the large hump in the exhaust port that restricts flow.
Cutaway of a cylinder head showing where to port and remove metal
For performance applications the large hump is usually removed from the exhaust port to
improve flow. For more serious applications more material is removed from the roof and the valve
guide pedestal creating a straight roof all the way to the back of the valve bowl. The sharp edges
in the valve bowl are usually smoothed as well. The floor of the port is usually not modified other
than port matching to the gasket and extending that into the port an inch or so. Removing very
much material from the floor may actually hurt flow.
A mildly ported exhaust port
This exhaust port has been
mildly ported and was port
matched to the gasket. The
hump was removed from the
center of the port with a die
Intake ports don’t require nearly as much work. Typically the bowl area under the valve is cleaned up
and deburred a little. Usually the valve guide pedestal is trimmed down a little and smoothed up
although this has never shown an improvement on a flow bench. There’s also a bulge on the intake port
wall where the push rod passage goes through the cylinder head and this is usually reduced slightly, but
care must be taken not to break through into the push rod passage. Port matching for both the intake
and exhaust ports to the gaskets being used is always performed.
Cutaway of a 302 cylinder head showing the intake port
Shown here is a cutaway of a 302 cylinder head exposing the intake port. The intake port was
considerably better than the exhaust port on these heads and usually just required some minor
clean up, bowl porting and port matching. You can also see the positive stop non adjustable
rocker arm stud used after 1965 in Ford small block heads.
Usually these modifications add about 40 CFM for the intake port and about 50 CFM for the exhaust
port at 0.500-inch valve lift or totals of around 195 CFM for the intake port and around 150 CFM for the
exhaust port. These are fairly substantial flow increases and along with a slightly bumped compression
ration from smaller chambers can produce some fairly large power increases on a typical engine,
especially on one with a mild camshaft.

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