1970 Mustang 429 Boss V8

1970 Mustang Engine Information & Specs – 429 Boss V8 (7.0 L)

429 Boss V8 Technical Specs & Data

1970 Mustang Engine Information – 428 cubic inch V-8 (7.0 L Boss V8)

429 Boss V8

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.

The block was a strengthened 429 cast block. They had HP429 cast into the front left side of the block. The 4 bold main engine had forged crank and connecting rods. The first 279 (model (820-S) engines used NASCAR type connecting rods, the remainder of the engines (model 82-T) used beefed up production type rods.

The aluminum heads used oversized valves set at an angle to each other placing the exhaust valves closer to the exhaust manifold and the intake valves directly in line with the intake manifold thus the breath- ability of the engine was maximized. This “crescent” design was similar to the hemi design used in other engines. There were no head gaskets use when assembling the 429. “O” rings were used to seal all water and oil passages as well as the individual cylinders.

An aluminum intake manifold was mated with a 735 cfm Holley carburetor. Valve covers were either magnesium or aluminum depending on date of production.

Engine Basics

Year 1970
bbl 4
Cylinders 8
Displacement 429 cu / 7.0 liters
Power (hp) 375 hp @ 5,200 RPM
Torque (lb/ft) 450 lb/ft @ 3,400 RPM
Compression 10.5:1
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 BOSS
Head bolts 90-95
Main cap bolts 70-80
Rod end caps 85-90
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 and BOSS)

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 1970
Seat angle Intake 30, Exhaust 45
Face angle Intake 29, Exhaust 44
Valve spring pressure lbs/inches 315 @ 1.31
Valve spring installed height (in) 1 13/16
Stem guide clearance (in) – Intake 0.0010 – 0.0024
Stem guide clearance (in) – Exhaust 0.0020 – 0.0034
Stem Diameter (in) – Intake 0.3715
Stem Diameter (in) – Exhaust 0.3705