Mustang MonthlyHow To Engine
Hard Core Resto Tech: Detailing a 428 Cobra Jet Engine Part 1
The most comprehensive guide to detailing a 428 Cobra Jet ever published
The Cobra Jet engine that was introduced in April 1968 is easily one of the most well-known engines of the late 1960s and early 1970s from the muscle car era. It is also one of the hardest to detail because, unlike a Boss or a Hi-Po engine, it was used in so many different applications and over several years. Not only in Mustangs, but also Cougars, Torinos, and Montegos. Different options could be added to the drivetrain like a manual or automatic transmission, with or without air conditioning, and with optional axle ratios. All of this affects how an engine is put together and detailed. The engine itself was officially rated at 335 hp and 418 lb-ft of torque, but the reality is the engine was producing around 411 hp. Because of how versatile the 428 engine was, it is considered one of the best powerplants Ford ever produced—so much so that eventually the Cobra Jet name was brought back and reintroduced in 2008 for the 40th anniversary of the release of the first Cobra Jet Mustang.
In March 1994, Mustang Monthly published an article by Bob Perkins that was one of the most detailed articles written on the subject. That article, like so many others of that time, was mostly with black-and-white photos. So here we will update that, plus add some more in-depth detailing items. Although not every single option and feature can be shown in this article, this guide should serve as a good basis for some of the common detailing tips and tricks.
1. The first step in detailing a 428 Cobra Jet engine is to make sure you actually have one, versus a 390 or standard 428 block. It is difficult to decode one when installed in a car, but when it is out there are a few things to look for. One of the easier things to look for is the “C” that is sand-cast in the back of the block, as shown in the pictures here. This is typical for a Cobra Jet block. If you see an “A” marked in the back of the block, most likely this is a standard 428 engine that was used in Thunderbirds, Mercurys, and LTDs. If there is no marking at all it is likely to be a 360, 390, or 410 block. This can be summarized as follows:
• “A” scratch on rear bulkhead with standard crank saddle webbing: August 1965-1966
• “A” scratch on rear bulkhead with reinforced crank saddle webbing: March 1967-June 1967
• “C” scratch on rear bulkhead with reinforced crank saddle webbing: June 1967-March 1970
1a. Of course another way to determine the correct block is the date code. This is cast into the block and visible right next to the oil filter adapter on the bottom of the engine block next to the oil pan, as shown here. Date code should be a few months prior to the build date of the car at the most.
1b. Nearly all FE blocks have a 352 that is cast in the front of the block. This first started with the 352ci engine in 1958 but was continued with the FE engine throughout its service life, including the Cobra Jet.
2. Cobra Jet engines used a special cast-iron head that can be identified with the engineering numbers C8OE-6090-N on the outside as shown here, and with inlet ports for the Thermactor system at each cylinder. These heads were used on all 1968 to 1970 Cobra Jet production cars that were built and always painted blue with the engine.
3. The VIN is typically stamped on the back of the engine block or on the back of the cylinder head. Before January 1968 Ford stamped these for warranty purposes and then only on high-performance engines. After January 1968 it was stamped on almost all blocks or heads as part of Department of Transportation regulations against automobile theft.
3a. The engine assembly date can be found typically stamped on one of the four flat spots near the cylinders with the most common being above the oil filter adapter. This will be dated after the casting date in a year, month, day, assembler last name initial format.
4. Exhaust manifolds were a cast-iron design and unique to the Cobra Jet engines. There are three different versions used between 1968 and 1970. The main difference in the manifolds during these years is in the passenger-side manifold. Version 1 does not have an additional reinforcement ridge at the front exhaust ports. Version 2 adds the additional reinforcement. Version 3 removes the need for an exhaust spacer. Manifolds should not have any blue overspray, as they were not on the engine when it was painted.
Version 1: C8OZ-9430-A. Note the lack of reinforcements compared to the next version. Used from 1968½ to early 1969 model year.
Version 2: C8OZ-9430-C. Note the addition of reinforcements compared to the previous version. Used from early 1969 model year to December 1969.
Version 3: C9OZ-9430-C. Removes the need for the exhaust spacer by machining the end to accommodate the H-pipe directly. Used from December 1969.
4a. Exhaust manifold bolts used were a special design that used ramp lock washers and flat washers shown here with the flat washers being placed against the manifolds. Correct finish of this hardware shown here.
5. A choke stove system was originally designed as part of the passenger-side exhaust manifold. This worked by running metal lines from the exhaust manifold via the choke stove to the carburetor to help with cold start. The exhaust manifold had a mesh filter element and an end cap fitting running to the line. These were used until 1970 when a manual choke was then used and eliminated this automatic choke. Note the original asbestos wrap that was used on the warm air tube.
5a. There was a design change in April 1969 that then added an additional input from the air cleaner to the choke stove system via an inline T that connected with an orange hose and the modifications you see here.
6. The water pumps used on the Cobra Jet engines are typically seen with two different casting numbers. C8AE-8505-H is normally seen on 1968 models. C9AE-8505-A is seen on 1969 and 1970 models. The difference being a larger internal bearing being used on the C9AE version. Both versions have date codes that are easily seen.
7. The paper engine ID tag was normally placed on the passenger front head on the flat area behind the smog pump. This tag identifies the engine and transmission combination that was pulled as a finished assembly to match the buildsheet. This tag would have a “D” and not an “L” because the 390, 427, and 428 engines were assembled at the Dearborn Engine Plant.
8. The metal engine ID tag was commonly placed under the coil bracket on the Cobra Jet engines. These tags were used by Ford from January 1964 to February 1973 on all its engines to identify them for production. Reading the numbers from top left to lower right would decode as 428 for the cubic-inch displacement of the engine; 70 would be the model year (not calendar year); the next digit is the revision level (in this instance 7); the next series of number/letters is the production date of the engine (0 A = January 1970); and the last set of numbers is the engine code that would match the buildsheet.
9. Original assembly line freeze plugs that were used are easily identified by the diamond logo in the center, although this logo is sometimes stamped on the back of the freeze plug and not visible when installed. These were serviced under part number C8AZ-6026-B and typically have a galvanized finish.
10. The intake manifold is cast iron and would be painted blue with the engine. The most common engineering number is a C8OE-9425-C that would be cast in behind the carburetor mounting area. At the very back of the intake is the date code that would be in a year, month, day format. This date needs to precede the build date of the car.
11. There were two basic versions of valve covers used on the Cobra Jet engines, plus one possible variant. Version 1 was the chrome valve covers that were used on 1968 and 1969 engines until February 14, 1969. These valve covers typically have a date stamp on them starting with the 1969 model year and are visible next to the oil breather area as seen above. Dates were in a month, day, shift format and did not include the year. After February 14, 1969, a finned aluminum valve cover was used with the engineering number C9ZE-6583-A or C9ZE-6583-C, which is stamped inside. The third version is an aluminum valve cover that has “428 Cobra Jet” stamped on the outside and was sold by Ford Enginesports as an accessory item. It has the engineering number C9ZE-6583-B stamped inside. It is possible that in some cases this valve cover was installed from the factory.
12. The chrome-style valve covers used staples to hold on the valve cover gaskets. There was one staple used per tab—5 per valve cover.
13. An inspector OK stamp that was typically applied after engine hot testing to the driver-side front valve cover as seen here.
14. Original valve cover gaskets themselves would be a cork style with a silver-colored sealer on them that is visible on the areas where it sticks out.
15. Original spark plug wires had a protective sleeve that was meant to prevent any burns as the wires wrapped over the Thermactor tubes. The end of the spark plug wires were orange and had AUTOLITE molded in and a unique re-enforced ring at the end of each boot. Each wire was date-coded according to the calendar year (68, 69, or 70) and the quarter (Q1 to Q4), and numbered for its respective position from 1 to 8.
15a. Original spark plug wire boots at the distributor cap are all not exactly the same, as some are molded differently to give extra clearance.
16. The correct original distributor cap has AUTOLITE cast into the top of the cap as shown here and is a black molded piece.
17. An original style distributor hold down (B8A-12270-A) is shown here with the correct installed position (tangs up) and a phosphate and oil finish held in place by a zinc hold-down bolt and lock washer.
18. The correct style ignition coil bracket assembly. Note the position of the notch that fits against the intake manifold and the correct finish.
19. The original Autolite yellow top ignition coils used had an ink stamp that may or may not be visible when installed on the engine. The ink stamp would include a date code that is in a year, month, week, shift format as shown here.
Also, the correct orientation of the ignition coil is shown here. Here you can see the terminals are turned toward the driver-side valve cover.
20. The distributors that were commonly used in the Cobra Jets are listed here with the engineering numbers that would be stamped in them. All of them would be date-coded in a year, month, day sequence and are stamped in such a way that they are only visible from the back of the distributor when installed. All distributors are single-point design with the exception being the 1970 manual transmission, which is a dual-point distributor. Note the machined surfaces, some of which are visible when installed on the engine. The distributor cap hold-down clips would be a phosphate finish and not painted.
Come back next month for Part 2, with Part 3 of How to Detail a 428 Cobra Jet following the month after that!