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In the upper RPM range, small
block Ford Hi-Po engines run out of
breath. Every road racer or engine
builder knows that. A 289 Hi-Po head
flows at a rate of 220 CFM through a
properly massaged intake port. A sim-
ilarly ported 351 Windsor head flows
at 240 CFM. A GT40 head flows at 260
CFM. Every increase in CFM yields
approximately one horsepower.
Ford developed the GT40 head in
1965. They referred to it as the 289
HD head (for “Heavy Duty”) – to keep
it from being confused with the HP
head (for “Hi-Performance”). They also
did not want it to diminish their Hi-
Performance parts line. These heads
initially used an XE part number
(Ford’s category for “experimental en-
gineering,” a non-production part)
until actual production began. Then
the castings were given the part num-
ber prefix C6FE. Actual production
numbers are not known but experts
put the figure somewhere between 500
and 1000 sets.
The GT40 heads were used only
on GT40 MK I race cars (not road
cars). They were also suggested for use
by Shelby American on 1967 Mustang
Group II (Trans-Am) racers. They
were only available from factory parts
sources such as Holman-Moody or
Shelby American (Shelby American’s
part number was S7MR-6049-A; Hol-
man-Moody used the Ford part num-
ber C6FE-6049-A). These heads were
available in 1966 and 1967 (and possi-
bly in 1968) until the supply ran out.
To give you an idea of their value, in
the 1966 Shelby American catalog,
dated 8/1/66, a pair of bare “HD” heads
from Shelby American were listed at
$425.00. Today, a clean set would sell
for between $5,000 and $10,000. If you
can find a clean set. Don’t forget, these
were purchased by racers who would
have used them on an engine – not by
some collector who would have put
them on a shelf and never used them.
Shelby American information de-
scribed S7MR-6049-A as a “
Special
Cylinder Head Kit. It includes fully
modified 289 CID cylinder heads for
sedan racing needs: larger 1.875-in. in-
take and 1.625-in. exhaust valves.
Springs, retainers, teflon valve stem
seals, etc. are furnished. Cylinder
heads should be used with the speci-
fied steel shim head gaskets shown in
the parts list. Output increases when
used in conjunction with the high per-
The SHELBY AMERICAN
Summer 2017 64
The Holy Grail of Ford small block road race engines has always
been the C6FE GT40 Head: nothing flows better, they were made
in extremely small numbers, they are impossible to find today
and excruciatingly expensive when they are.
Guess what? They are finally available again.
– Rick Kopec
The primary way of identifying a GT40 head is by the part number cast into the under-
side of the exhaust port [
fresh 2017 casting pictured
]. GT40 heads also have noticeably
larger intake and exhaust valves when compared to a C5OE Hi-Po head. The original
GT40 heads, cast in 1966, had “C6FE” cast below the intake port [
not shown
] and did
not have the full part number cast into them..