1971 Mustang Engine Information – 428 cubic inch V-8 (7.0 L Super Cobra Jet V8)
Ford 429 Super Cobra Jet
The Boss 429 engine was offered late in 1969 and was rated at over 370 horsepower. It had aluminum heads with extremely large free flowing ports, contoured exhaust manifolds, a high rise intake manifold to help it gain horses.
Ford offered the Super Cobra Jet version of the 429. The 429 Super Cobra Jet (429SCJ) was fitted with a Holley 735 cu ft/min (20.8 m3/min) 4-bbl carburetor, larger mechanical camshaft, and a four-bolt main block. The engine output was increased to 375 hp and 450 lb-ft of torque, coming with a 3.91:1 or 4.30:1 rear axle ratio
With the 427 and 428 engines now history, the replacement 429 CJ engine was called for duty as the top Mustang engine. Although the 429s were available on any Mustang body style, the big engine was most often seen in the Mach 1, which was still the main Mustang performance model. The 429 belonged to the Ford 385 Engine Series and as such, no parts were interchangeable with the older 428. Wider, larger, and heavier, the 429 would not readily fit into the 1970 Mustang engine compartment, which is one of the reasons why the 1971 Mustang got bigger. The cylinder block was a variation of the 429/460 block, of which the Boss 429 was also based on; the cylinder heads were similar to the 351 Cleveland in design. You could describe the 429 as a large Boss 302.
As equipped in the Mustang, the 429CJ came with four-bolt mains, forged rods and pistons, 11.3:1 compression ratio, a hydraulic cam, (similar to the Boss 429’s) very large ports and valves, and all 429CJs came with aluminum valve covers. The 429CJ came with a Rochester Quadrajet four-barrel carburetor, and some early units had adjustable valve trains. The 429CJ became a 429SCJ if the Drag Pack option was ordered.
It consisted of a 3.91 or 4.30 rear axle ratio with Traction Lock or a 4.11 ratio with a Detroit Locker rear. Both of these engines have the engine code C. Some Mustangs with the Drag Pack also included an external engine oil cooler, though of a different design than previously used. The SCJ engine came with a Holley 780 cfm carburetor rather than the Rochester Quadrajet, a mechanical lifter camshaft and adjustable rocker arms.
Engine Basics
| Year | 1971 |
| bbl | 4 |
| Cylinders | 8 |
| Displacement | 429 cu / 7.0 liters |
| Power (hp) | 375 hp @ 5,600 RPM |
| Torque (lb/ft) | 450 lb/ft @ 3,400 RPM |
| Compression | 11.3:1 |
| Bore x Stroke | 4.360 x 3.590 |
Engine Torque Specifications
All torque specifications provided in this table are those recommended by FORD. If you use special bolts, follow the torque specifications provided by the manufacturer. I recommend that you use the 3 step torque technique where you torque down the bolts in three equal steps. Once you have reached the maximum recommended torque setting, go around one more time. Do not torque in a circular pattern. Always torque cross to cross.
| 429 Std. | |
| Head bolts | 130-140 |
| Main cap bolts | 95-105, 16 bolts 70-80 |
| Rod end caps | 40-45 |
| Intake bolts | 25-30 |
| Exhaust manifold bolts | 28-33 |
| Harmonic damper | 70-90 |
| A/C Compressor mounts | |
| Engine fan | |
| Motor mounts to engine | |
| Bellhousing bolts | |
| Trans to bellhousing | |
| Flywheel to Crankshaft | 75-85 |
| Oil pan bolts | 12 |
| Valve cover bolts | 10 |
| Carburetor mount bolts | |
| Oil pump | |
| Spark plugs | |
| Trans. inspection plate | |
| Water pump bolts | |
| Clutch pressure plate | |
| Water pump | 20 |
| Upper cam gear | |
| Rocker arms | |
| Main cap cross bolts |
Crankshaft Bearing Journal Specifications (Boss 429)
Main Bearing Journal (inches)
| Journal Diameter | 2.2994 – 3.0002 |
| Oil Clearance | 0.0010 – 0.0025 |
| Shaft end play | 0.004 – 0.008 |
| Thrust on number | 3 |
Connecting Rod Journals
| Journal Diameter | 2.4992 – 2.500 |
| Oil Clearance | 0.008 – 0.0025 |
| Side clearance | 0.010 – 0.020 |
Piston Ring Specifications
Comp Ring Width
| Top | 0.077 – 0.078 |
| Bottom | 0.077 – 0.078 |
Ring side clearance
| Top | 0.002 – 0.004 |
| Bottom | 0.002 – 0.004 |
| Oil ring | Snug |
Ring gap width
| Top | 0.010 – 0.020 |
| Bottom | 0.010 – 0.020 |
| Oil Ring | 0.010 – 0.035 |
Piston Specifications (429 SCJ)
| Code Red | 4.3569 – 4.3575 |
| Code Blue | 4.3581 – 4.3587 |
| 0.003 Oversize | 4.3593 – 4.3599 |
| Piston to Cyl. Bore clearance | 0.0030 – 0.0038 |
| Piston Pin Bore Dia. | 1.0402 – 1.0405 |
Valve Specifications
| Year | 1971 |
| Seat angle | 45 |
| Face angle | 45 |
| Valve spring pressure lbs/inches | 229 @ 1.33 |
| Valve spring installed height (in) | 1 13/16 |
| Stem guide clearance (in) – Intake | 0.0010 – 0.0027 |
| Stem guide clearance (in) – Exhaust | 0.0010 – 0.0027 |
| Stem Diameter (in) – Intake | 0.3420 |
| Stem Diameter (in) – Exhaust | 0.3420 |
