Beginning with the 1968 model year, all vehicles sold in the USA were required to meet new federal standards for hydrocarbon (HC) and carbon monoxide (CO) emissions. One of the more effective ways to reduce these pollutants was through the use of a thermal reactor (thermactor) system. Thermactors inject pressurized air immediately downstream of the exhaust valve in order to continue the combustion reaction to reduce the amount of HC and CO at the tailpipe.
The 428 CJ thermactor system was based on the 1967 California emissions 390 GT system and remained common with the 390 GT through the end of production in 1970. The system included a belt driven air pump with sealed bearings, a vacuum operated flow control valve, check valves, mounting brackets, distribution hoses and steel tube manifolds with injection tubes to direct the air into the exhaust ports of both cylinder heads.
While the majority of the thermactor system stayed the same, there were four different driver's side air injection manifolds used between 1967 and 1970. It's interesting to note that the part numbers listed in the MPC don't fully reflect these changes. It is also interesting that the MPC lists two different part numbers for the passenger side manifold during the same period, however this manifold has no apparent changes.
The first version of the driver's side manifold was installed on 1967 390 GTs. The second version was introduced with the 1968 model year and included changes to the manifold header tube that may have been required to accommodate the taller valve covers of 1968 Shelby GT500s. The next version, introduced later in the 1968 model year, had a modified mounting bracket foot. The fourth version was introduced early in the 1969 model year and included another change to the manifold header tube.
We have not been able to document any unrestored "135" CJ Mustangs so it is currently unknown whether they were assembled with the early or late 1968 style driver's side manifold. In either case, it is reasonable to expect that they would have been the same as what was installed on 390 GT Mustangs built during the same time period. We do know that the transition to the later 1968 driver's side manifold had occurred before the earliest confirmed unrestored 428 CJ Mustang GT was built in mid-February 1968. This manifold was used throughout the remainder of the 1968 model year.
At this time, we have not been able to document the introduction date of the 1969/1970 style driver's side manifold based on unrestored original cars. Since the 1968 MPC date for the introduction of the C9ZZ-9B445-B driver's side manifold closely aligns with the introduction of the 1969 model year, it is likely that this is the 1969/1970 manifold.
Drivers side manifold configurations from Ford MPC:
From August 1968 MPC:
1968 Mustang left (before 8/12/68): C7ZZ-9B445-C
1968 and 1969 Mustang left (after 8/12/68): C9ZZ-9B445-B
From an MPC page dated April, 1970:
1968 - 1970 Mustang left: C9ZZ-9B445-B
Observed driver’s side manifold configurations:
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| 1967 Driver's Side Manifold Photo Courtesy Chris Teeling |
1967 Driver's Side Manifold Details Photo Courtesy Paul Byrnes |
1967: (used on 390 GT cars sold in California) The mounting bracket foot is flat. The manifold header tube is routed from the anti-backfire valve to the horizontal run forward of the #5 branch. The #5 branch tube is the same as #6 and #7 tubes.
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| Early 1968 Driver’s Side Manifold Photo Courtesy Chris Teeling |
Driver’s Side Manifold Tube Comparison Photo Courtesy Jim Woods |
Early 1968: The manifold header tube was re-routed out and around the valve cover then down to the horizontal run between #5 and #6 branches. The branch for #5 exits the header tube and runs down and forward.
Late 1968 Driver’s Side Manifold
Photo Courtesy Kerry Wortman
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| Driver’s Side Manifold Bracket Detail Photo Courtesy Chris Teeling |
Driver’s Side Manifold Bracket Detail Photo Courtesy Alan Payne |
Late 1968: Same as early 1968 except a bend was added to the mounting bracket foot. This bend makes it a bit easier to get a wrench onto the left front intake manifold bolt.
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| 1969 Driver’s Side Manifold Photo Courtesy Chris Teeling |
1968 and 1969 Manifold Comparison Photo Courtesy Ed Meyer and Chris Teeling |
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| Late 1968 Photo Courtesy Kerry Wortman |
1969 Photo Courtesy Chris Teeling |
1969/70: Same as late 1968 except the header tube between the first and second bends downstream of the anti-backfire valve is about 1 inch shorter than on the 1968 manifolds.
Passenger side manifold configurations from Ford MPC:
From August 1968 MPC:
1968 Mustang right: C7SZ-9B445-A
1969 Mustang right: C9ZZ-9B445-A
From April 1970 MPC:
1968 Mustang right: C7SZ-9B445-A
1969 and 1970 Mustang right: C9ZZ-9B445-A
Observed passenger side manifold configuration:
1968 Passenger Side Manifold
Photo Courtesy Kerry Wortman
1969 Passenger Side Manifold
Photo Courtesy Chris Teeling