428 Cobra Jet vs. 428 Super Cobra Jet

Printer-friendly versionSend link via emailSave as PDF

What are the differences?

What makes the 428 Super Cobra Jet engine so super?

The 428 SCJ was first introduced during the 1969 model year. Mustang buyers who selected either of the optional 3.91:1 or 4.30:1 rear end gear ratios got more than just an optional axle ratio! Ordering either of these axle ratio options commonly triggered a few other upgrades as well, including the 428 Super Cobra Jet engine, an external oil cooler mounted in front of the radiator, and relocation of the driver's side horn to the passenger side of the radiator core support to make room for the oil cooler. Starting in February 1969 this complete package could be ordered as the "Drag Pack" option. Note that it was not thought to be possible to order an SCJ engine by itself -- the only way to get your hands on an SCJ in a Mustang was to order the optional 3.91:1 or 4.30:1 rear end gear ratios.

There have been rumors of cars being delivered with SCJ engines and other axle codes, and V- or W-code axles and no SCJ engine. To date I've only seen documentation for one such anomaly: 9R02R103630, built with a W-code 4.30:1 rear axle and a standard CJ engine. According to statistics courtesy of Marti Auto Works and copyrighted, this car was built at the San Jose assembly plant on October 1, 1968. The axle code in the order image is "8" (which means 4.30:1 traction-lok) and the car's data plate has an axle code of "W". However, the Ford production database describes the car as having an S-code 3.50:1 traction-lok rear. The error is described on the owner's Marti report; here's an excerpt. Note that the explanation says that three other cars were built like this at San Jose! Makes you wonder how many were built at the other plants.

SCJ external oil coolerSCJ relocated horn assembly
External oil coolerRelocated horn assembly

The basic strength of the Super Cobra Jet engine is in a more durable reciprocating assembly (crank, rods, pistons, wrist pins, flywheel/flexplate, and harmonic balancer) that was designed to withstand the higher RPM requirements of drag racing. For example, the SCJ used race-proven 427 "LeMans" capscrew connecting rods with shorter bolt heads, whereas the standard CJ rod used a more common press-fit bolt and nut to retain the rod cap. The SCJ timing pointer is slightly longer to clear the larger harmonic balancer.

Connecting rod research seems to indicate that CJs used a variety of common high-end FE rods, with the C7AE-B rod being fairly common. I've heard from others who've reported finding C6AE-C, C6AE-D, and C6AE-F rods in what they believe to be original engines. I've seen written reference to a C9AE-C rod also being used, but I've never been able to confirm an installation. SCJs seem to use the C6AE-E rod most frequently, though again I've seen written reference to a C9ZE-A rod that I haven't been able to confirm was ever actually factory installed.

A common misconception seems to be that SCJs were originally equipped with forged pistons and CJs were originally equipped with cast pistons. George Anderson of Gessford Machine was kind enough to point me to a page from Ford's "Muscle Parts Description and Interchange" book, a supplement to the original "Muscle Parts" catalog that was published in July 1970, that clearly states that "all 428 engines use "dished" cast aluminum pistons with two sets of eyebrows cast so they can be used in right or left bank".

It appears that Ford went through at least three piston designs during the 428 CJ and SCJ production run to address durability problems. The later piston, which appears starting around December 1968, is marked "428" and "SUPER" (thanks to Randy Pollock for the picture), and differs from the earlier pistons by having additional metal in the pin boss area. The "SUPER" mark does NOT mean that the pistons were used only in SCJs! Though different part numbers were used for standard sized CJ and SCJ pistons (perhaps to provide slightly different installation tolerances), most folks that I've talked to believe that the pistons were in fact identical.

None of the parts of the 428 SCJ reciprocating assembly interchange with their 428 CJ counterparts. Mixing SCJ and CJ parts can cause severe balance problems. It may be possible to mix components if every component of the reciprocating assembly is dynamically balanced, but why bother?

It's important to note that all other components of the SCJ engine do in fact interchange with the CJ engine. Block, heads, manifolds, etc. are identical. Some original SCJ blocks were stamped "super" on the front; if present, this marking was likely there to tell the original engine assemblers to use SCJ internals when building the engine (here's an example of such a stamping courtesy of Randy Pollock). Factory horsepower and torque ratings were the same for both CJ and SCJ engines.

"Detroit Locker" Differentials

Most 428 Cobra Jet fans have heard of the "Detroit Locker" differential, a positive locking differential that was originally produced by Detroit Automotive Products Corporation (DAPCO) and is now available from TracTech Inc. Most of the published literature that I've read says that buyers of the locking 4.30:1 rear end gear also got a gear-driven Detroit Locker instead of Ford's clutch-packed Traction-Lok, but recent research leads me to believe that this is NOT the case! Information provided by Phil Wassil and by Kevin Marti of Marti Auto Works documents Detroit Locker availability beginning around November 1969 - in the 1970 model year! Kevin later explicitly confirmed that "Ford did not produce 69 4.30 vehicles with Detroit Lockers. These only became available in the 1970 model year, as you noted. There was a special designation in the database to tell which cars had these installed". During the 1970 model year, "DETROIT LOCKER DIFFERENTIAL" appears on the invoice of vehicles that came with a factory Detroit Locker.

The table below summarizes the part differences between the two engines. Pictures of some of these parts can be found in the component identification section of this web site.

Model Year
1969
1970
Engine Type
CJ
SCJ
CJ
SCJ
1UB or
1UB and A
1UA or
1UA and B
1UB and A
1UA and B
Connecting Rods
C7AE-B
C6AE-E
C7AE-B
C6AE-E
Pistons* (6108)
Cast
C9ZZ-Y (R)
C9ZZ-Z (B)
Cast
C9ZZ-N (R)
C9ZZ-R (B)
Cast
C9ZZ-Y (R)
C9ZZ-Z (B)
Cast
C9ZZ-N (R)
C9ZZ-R (B)
C8OE-A
C9ZE-A
C8OE-A
C9ZE-A
Flexplate* (6375)
C6AZ-B
C9OZ-B
C6AZ-B
C9OZ-B
C8AE-A1, A2
C8AE-C
C8AE-A1, A2
C8AE-C
Balancer Counter Weight
N/A
C9ZE-A
N/A
C9ZE-A
C9AZ-A
C9OZ-A
C9AZ-A
C9OZ-A

1969 and 1970 CJ vs. SCJ parts identification

* These are service part numbers, not engineering numbers. Though I've seen references to engineering numbers on flexplates, I've never actually seen any kind of stamped or cast number on a flexplate. If you have, please consider sharing your information and pictures, if possible. Piston part numbers are marked (R) for red size and (B) for blue size to note options for selective fit based on normal production tolerances.

** I've also read reports of 428 CJ balancers with engineering numbers C8AE-AA and C8AE-AB, but I haven't personally seen one of these balancers -- have you? If so, please consider sharing a picture.

The "Drag Pack" Controversy

Lots of people have different opinions about the "Drag Pack" option described above, what it included, and which cars it was available for. I'm not going to provide an opinion, but I will show you how Ford Motor Company described this Mustang option on their 1969 and 1970 option price lists. First, the 1969 price list:

1969 Drag Pack Description

April 17, 1969 Mustang Drag Pack Option Description

Now, the 1970 price list:

1969 Drag Pack Description

June 1, 1970 Mustang Drag Pack Option Description

Observations:

  • Note that there is no mention of the Detroit Locker in the 1969 description, but it's clearly listed in the 1970 description.
  • The 1969 description says that the Drag Pack option is "Available only with 428 CID 4V Non-Ram or Ram Air engines" and "Not available with other optional ratio axles or air conditioner". The 1970 description says "Available only with 428 CID 4V Cobra or Cobra Jet engine" and "Not available on Boss 302, or with other optional ratio axles".

Images Provided by Members and Friends

Cobra Jet Connecting Rod
Cobra Jet Crankshaft (engineering number detail)
Super Cobra Jet Connecting Rod
Super Cobra Jet Crankshaft
Super Cobra Jet oil cooler adapter
Super Cobra Jet harmonic balancer counter weight, 1
Super Cobra Jet harmonic balancer counter weight, 2
Super Cobra Jet harmonic balancer counter weight, 3
Super Cobra Jet harmonic balancer counter weight, 4
Super Cobra Jet harmonic balancer
Super Cobra Jet horn detail (note the jumper wire and reinforcement bracket)
Super Cobra Jet horn reinforcement bracket
Super Cobra Jet horn jumper wire