The 400 V8: Final Mopar Big Block Engine

The first B engine was launched in the 1958 model year, in 350 and 361 cubic inch versions. They were quite similar to the company’s existing Hemi V8 engines, but used wedge-shaped heads to dramatically cut costs, weight, and engine size. Conventional in every way, the pushrod V8s were nevertheless capable of quite high performance.

400 V8

For years, the largest “B” engine was the 383 cubic inch V8; starting with the 1959s, a new series, dubbed “RB,” used a raised block and went up to 440 cubic inches.

In the late 1960s and early 1970s, Chrysler started working on a new engine which would cut costs by standardizing all the big block engines (B and RB alike) on a 4.32” bore, according to racer and historian Rick Ehrenberg. Switching the 383 to that bore would have brought a displacement of 396 cubic inches, but the marketing people felt 400 sounded better — and that’s what they got, though it meant using a bore of 4.34”, defeating one purpose of the new engine.

1972 Carburetor Net Horsepower Torque (lb-ft)
360 4-barrel. 175 @ 4,000 285 @ 2,400
4002-barrel190@ 3600 310 @ 3200
4404-bbl 225 @ 4,800345 @ 3200

This was the largest B engine ever made; the stroke was the same as the other B engines (383, 361, and 350), but the bore was larger than any B or RB engine. Compression was 8.2:1, lower than optimal as an easy way to reduce emissions. Power was actually similar to the base 440.

In its first year, powering 1971 cars, there was only one 400 V8 — a two-barrel — using the Ball & Ball (later Carter) BBD downdraft, with a 1 5/16” venturi and 1 9/16” bore. The idle speed was set to 700 rpm; the fast idle speed, at 1700 rpm. The automatic choke was controlled by a thermostatic coil spring, and defaulted to two notches rich. Ignition was via distributor and points at first (the points replaced by electronic ignition within two years); plugs were Champion J-11Y or Mopar P36P, gapped to the usual 0.35”. As with all Mopars of the day, the ballast resistor could fail without warning, leaving the car un-startable.

The camshaft intake valve duration was 260°; the exhaust duration was 268°; and the overlap was 38°. As with all Chrysler engines of the time, it used a timing chain; and to ease maintenance, tappets were hydraulic and self-adjusting. Valves were 2.08” (intake) and 1.75” (exhaust; sometimes reported as 1.74”). The crankshaft was fully counter-balanced. A later 400 High Performance engine used a cam with 268°/284°/46° (the crank on these was still forged steel, though the standard 400 used cast ductile iron).

1974400 horsepower 440 horsepower
2-barrel185 @ 4,000
4-barrel205 @ 4,000230 @ 4,000
4-barrel HP250 @ 4,800275 @ 4,400
Police240 @ 4,800275 @ 4,400

The engine had a traditional rotary full pressure oil pump, driven by the camshaft, with a minimum of eight PSI at idle, and a spin-on full-flow oil filter; the engine took five quarts of oil, with the filter. The engine used a two-plane intake manifold.

CID BoreStroke
383 4.033.375
400 4.3423.375
4404.323.75

Starting in 1973, exhaust-valve seats were induction-hardened for use of lead-free fuels. In the hardening process, seats reach a temperature of 1700°F and are then allowed to air-cool. This hardened the valve­seat surfaces to a depth of .05" to .08" which gives them greater resistance to wear than unhardened seats.

Maintenance was eased and reliability increased in the same year (1973) by the addition of the Chrysler electronic ignition system, which had been launched in some 1972 cars.

1976horsepower torque
2-barrel175300
4-barrel Lean Burn210305
4-barrel HP240325

Note: for 1976, the only California-legal 400 was a four-barrel with 185 hp and 285 lb-ft.

Police and high performance versions used higher rate valve springs and surge dampers to prevent valve float. Truck versions used shot-peened nodular iron crankshafts for durability (the 440 had forged cranks for trucks and police cars).

In 1974, the 400 used a Holley R-6737A two-barrel carburetor, with a 1.56” barrel; the 400 “HP” used a Carter Thermoquad four-barrel (1.50 primaries, 2.25 secondaries). This was not the same carburetor as the 440, but it was similar in dimensions and identical in barrel sizes. All the 400 and 440 cubic inch engines used premium fuel at this point, and had 8.2:1 compression. New oval intake snorkels increased engine output slightly on the 1974s by reducing air turbulence.

1974 400

From 1973 to 1978, emissions equipment continued to become more complex, as engineers tried to get carburetors to work more efficiently under all conditions. Tuning chief Pete Hagenbuch asked for fuel injection, but it was rejected due to cost (most likely far less than the cost of extra warranty work and lost customers). Electronic Lean Burn, the world’s first computerized spark advance system, helped — but had its own problems. To save money, cast crankshafts started to replace the forged crankshafts of prior years.

The 1978 cars with 400 cubic inch V-8 engines gained dual concentric throttle return springs in addition to a torsion throttle spring.

The heat valve in the right exhaust manifold diverted hot gases to the floor of the intake manifold which helps to vaporize the fuel mixture when the engine is cold, speeding warm-up; a thermostatic spring reduced gas flow through the intake manifold crossover passage.

The 1978s also had an adaptor for timing the ignition magnetically; it could still be set by timing lights.

The last big block Chrysler engine was produced in August 1978; they were still standard in the 1978 Chrysler Newport and New Yorker (the 440 was optional). In this application, the 400 had a four-barrel carburetor, had the same 8.2:1 compression, and was rated at 195 horsepower and 305 pound-feet of torque. It was also listed for sale in Dodge trucks, e.g. as a $72 option for the D100 and D200.

The last vehicle built with one was made in 1979 — a pickup truck.

1972400 cid 90° V8
Compression 8.2:1
Min compression100 psi
Max variation between cylinders40 psi
Firing order1-8-4-3-6-5-7-2
Timing2.5° BTC
Left bank, front to rear1-3-5-7
PistonsAuthothermic, steel struts
Piston weight768.5 grams
Piston pinsPress fit in rod
Piston rings2 compression, 1 oil
Connecting rod weight812 grams
  

 

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