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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. Similar in some ways to the existing Hemi V8 engines, the B series used wedge-shaped heads to slash costs, weight, and engine size. Though conventional in design, the pushrod V8s were capable of high performance, and garnered a reputation for durability.

400 V8

For years, the largest “B” engine was the 383 cubic inch V8. The company created a raised block with the 1959 cars; the new “RB series” would go up to 440 cubic inches. The numerous engine sizes raised costs a bit, so Chrysler started working to standardize all the big block engines on a 4.32” bore (according to racer and historian Rick Ehrenberg). Using that bore with the 383’s existing stroke 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”, which some would say defeated the purpose.

1972 Carburetor Net Horsepower Torque (lb-ft)
360 4-barrel175 @ 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 so they could reduce emissions.

Despite its size, the 400 has often been dismissed as a low-powered “smog engine.” It was basically an over-bored 383 with an 8.2:1 ratio for emissions and mildly longer cam timing events and higher lift (on the four-barrel version). However, as “CBody67” pointed out, the engine was always rated with net horsepower; many were confused by the move from gross to net, which dropped ratings by up to 50 hp. It didn’t help that the first-year 400s all had two-barrel carburetors.

In the 1971 cars, the 400 V8 used the Ball & Ball (later Carter) BBD downdraft, with a 1 5/16” venturi and 1 9/16” bore. For the 1972 cars, they used the Holley 2210 two-barrel. The huge displacement, topped by a two-barrel, gave the 400 somewhat less of a reputation than it may have deserved, but it was generally just about 25 horsepower less than a similarly equipped 440.

In its first year, the idle speed was set to a fairly low 700 rpm; the fast idle speed, at 1,700 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, gapped to the usual 0.35”.

1974 horsepower400 440
2-barrel185 @ 4,000
4-barrel205 @ 4,000230 @ 4,000
4-barrel HP250 @ 4,800275 @ 4,400
Police240 @ 4,800275 @ 4,400

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).


The engine had a traditional rotary full pressure oil pump, driven by the camshaft; it had a two-plane intake manifold. To the very end of production, the 400 four-barrels all had roller timing chains, windage trays, chrome moly rings, better bearings, and some other performance/durability features which had begun with the Road Runner 383. They were still used by many law enforcement agencies, which needed high speed durability and reliability.

Electronic ignition was optional at first, but many dealers ordered it; then it was standard in the 1973 cars. As with all electronic-ignition Mopars of the day, the ballast resistor could fail without warning, leaving the car un-startable; veterans learned to spend $4 on a spare and kept it in the glove compartment, since the swap could be made easily at a parking space or road shoulder.

The 1973 cars were also the first to get induction-hardened exhaust valve seats, so they could use unleaded gasoline when the supply of leaded fuel ended, around ten years later. The seats were heated to 1,700°F and then allowed to air-cool, hardening the surfaces to a depth of .05” to .08”.

1976horsepower torque
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. 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, many due to the lack of proper materials, and many owners replaced it. 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 400 was standard on the popular Chrysler Cordobas in most, but not all years.

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.

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

Tuning and other experiences

From CBody67

To set the base idle speed, I’d put it in gear, parking brake full on, and adjust the idle speed to just where it became a smooth flow from a flow of individual pulses — then put it in Park and see where the “unloaded” idle speed went to. Then adjust the idle mixture from there, re-tweaking the idle speed in gear.

If things were right, it would idle smoothly all day with the a/c on in gear. There would be no real hydrocarbon smell on my hand as I checked for the exhaust pulse; it was the lean best idle that worked.

In this process, the 400 had a much hotter exhaust temperature than the 383; the lower compression motors allegedly had higher heat rejection, which helped cook the emissions. It impressed me was that the factory tune-up specs (on the underhood decal) for ignition timing were stated as + or - 2 degrees — they were enough under the emissions requirements that they had some room to play with.

Most of the people who replaced the Lean Burn really didn’t get the best results; they used an earlier carb with a Direct Connection electronic ignition kit, or replaced the distributor with a remanufactured one, resulting in a car that ran, but not well.

In the 1976 model year, the 400 HO still had no catalytic converter, with a “Non-Catalyst” sticker on the driver’s door.

The 1978 Chrysler service manual lists converter stall speeds; the “Road Runner 383” converter was the normal 225 Slant Six torque converter, with a higher stall speed behind the more powerful 383. The normal 383 and 440s got the 11.75” converter, as the Road Runner converter was 10.75”. The stall speeds quoted for the 1978 HO engines were between 2800-3200 rpm, while many GM converters were rated to 2000 rpm. These “loose” factory converters, coupled with the internal guts for the 400 and 440s, meant that Chrysler was probably the only OEM building true high performance cars with lower compression ratios, doing what they could with longer cam timing specs and such. The exhaust system was still large, too; and when Chrysler did a dual exhaust car, it had two separate converters. GM used one, with a dual outlet exhaust.

The 400 heads’ ports looked a little different and were initially perceived to be lower performance than the 906 castings of 1971 and earlier. Later, when the 906s and the later ones were ported identically, the flows were found to be the same.

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