1973 Mustang Engine Information – Thriftpower Inline 6 (250 cubic inch)
Introduced in 1969, the 155 horsepower 6 cylinder was needed because of the Mustang’s increase in size. The 200 cubic inch six although still offered was way underpowered to handle the new Mustang. However, in my opinion, to really power a Mustang always required an 8 cylinder engine and buying a 6 (or 4 cylinder in later years) was like buying 3/4 or 1/2 an engine. But you didn’t get a discount from the dealer for the part of the engine they forgot to install.
Engine Basics
| Year | 1973 |
| Cylinders | 6 |
| Displacement | 250 cu / 4.1 liters |
| Power (hp) | 99 hp @ 3,600 RPM |
| Torque (lb/ft) | 184 lb/ft @ 1,600 RPM |
| Compression | 8.0:1 |
| Bore x Stroke | 3.682 x 3.910 |
Engine Specs (250 cid inline 6)
| Spark Plugs | |
| Oil filter | |
| Gas Filter | |
| Air Filter | |
| PCV | |
| Oil Pressure | 35 – 55 PSI |
| Points | Gap and Dwell at xxx RPM |
| Timing | 6 Degrees BTDC Manual & 12 Degrees BTDC Automatic |
| Valve adjustment | |
| Valve size | |
| Valve arrangement | E I E I E E I E I I E Front to rear |
| Manifold Vacuum | 17 inches at idle |
| Warm Idle Manual Trans | 575-600 RPM |
| Warm Idle Auto Trans | 500-525 RPM |
| Carburetor CFM | |
| Bore and stroke | 3.500 X 2.940 |
| Compression | 9.1:1 (155 – 199 psi @ cranking speed) |
| HP and Torque | 101 hp at 4400 RPM and 158 ft/lbs torque at 2400 RPM |
| Taxable HP | 29.4 |
| Distributor Rotation | Counter-Clockwise |
| Firing order | 1 – 5 – 3 – 6 – 2 – 4 |
Clutch information: for the 3 spd, 9″ diam. 6 Springs, Pressure plate orange cover, purple springs, aluminum stripe. Disc is 9″ diameter, 6 springs, Blue with blue springs.
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.
| Head bolts | 70-75 |
| Main cap bolts | 60-70 |
| Rod end bolts | 19-24 |
| Intake bolts | |
| Exhaust manifold bolts | 13-18 |
| Harmonic damper | 85-100 |
| A/C Compressor mounts | |
| Engine fan | |
| Motor mounts to engine | |
| Bellhousing bolts | |
| Trans to bellhousing | |
| Flywheel to Crankshaft | 75-85 |
| Oil pan bolts | |
| Valve cover bolts | |
| Carburetor mount bolts | |
| Oil pickup | |
| Spark plugs | |
| Trans. inspection plate | |
| Water pump bolts |
Crankshaft Bearing Journal Specifications
Main Bearing Journal (inches)
| Journal Diameter | 2.3982 – 2.3990 |
| Oil Clearance | 0.0005 – 0.0022 |
| Shaft end play | 0.004 – 0.008 |
| Thrust on number | 5 |
Connecting Rod Journals
| Journal Diameter | 2.1232 – 2.1240 |
| Oil Clearance | 0.008 – 0.0024 |
| Side clearance | 0.003 – 0.010 |
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 | 0.015 – 0.055 |
Piston Specifications
| Code Red | 3.6778 – 3.6784 |
| Code Blue | 3.6790 – 3.6796 |
| 0.003 Oversize | 3.6802 – 3.6808 |
| Piston to Cyl. Bore clearance | 0.0014 – 0.0020 |
| Piston Pin Bore Dia. | 0.9122 – 0.9125 |
Valve Specifications
| Year | 1973 |
| Seat angle | 45 |
| Face angle | 44 |
| Valve spring pressure lbs/inches | [email protected] |
| Valve spring installed height (in) | 1 19/32 |
| Stem guide clearance (in) – Intake | 0.0008 – 0.0025 |
| Stem guide clearance (in) – Exhaust | 0.0010- 0.0027 |
| Stem Diameter (in) – Intake | 0.3104 |
| Stem Diameter (in) – Exhaust | 0.3102 |
