The Amazing Mopar (Dodge/Plymouth) 340 V8 Engine

Thanks to Danny Frost, Steve Silver, Joshua Skinner, Carl Payne, Dan Stern, Steven Havens, H. David Braew, Jim Forbes, Jamie Bergen, Mike Sealey, and Peter Duncan.

Introduction to the 340

chrysler 340 V8 engine One of the best engines of the 1960s and 1970s for performance enthusiasts was the 340 V-8. It had high-flow heads, big ports, a two-level intake manifold, and a six-barrel option (three two-barrel carbs). The package allowed for high speed with the light weight helping handling.

The 340 cars gave away nothing to the 383 cars in a straight line, and were ahead of the 383 cars on anything involving turns — and spark plug access.

When the 340 came out in late 1967, it was a street fighter from the start. Separating the 340 from the standard-performance 318 were not just 22 cubic inches, but also:

a dual timing chain with a windage tray to improve top end engine RPM by keeping the crank counter weights from 'churning the oil' in the pan.
2.02 inch intake valves and 1.60 inch exhaust valves
a high-rise dual plane intake
an 850 cfm carburetor (from 1971 to 1973)
a steel crank (through 1973, when a cast iron crank was used)
high-performance heads
a revised oil pump with a 90 degree adaptor
a special carburetor and cam

The 340’s best power rating was 290 horsepower; even in 1973, it still managed 245 net horsepower. A good-running, early 340 in a lightweight A-body or Road Runner embarassed many big block engines. Though relatively few were made, many parts interchange with 318s and 360s.

1970-71 engines were painted orange; they changed to blue in 1972-73, although some late 1971 engines ended up blue also.

In 1971, the 340 came with the J heads and 2.02/1.60 valves. Since 1971 saw the introduction of the "360 style" J head, they used the same casting for 1971 340s and 360s, with different machining for the different sized valves. The 360 head actually saw first limited use in the 1970 340 Six-Pack AAR/TA, which also had 2.20/1.60 machined heads.

In 1972, the 340 was seriously detuned, ostensibly for emissions reasons (but possibly also for insurance reasons). It went from a 10.4:1 to a 8.5:1 compression ratio, got smaller intake valves, and seriously fell in performance. 1973 was its last model year.

Parts from the 340 were transferred to a muscle version of the 360 in 1974. The high performance (HP) 360 went on to appear in A-body and F-body police cars, as well as the Little Red Truck and other fast pickups.

Development engineer Pete Hagenbuch wrote: I drove a 1972 Road Runner with the 340 for a year. For just driving pleasure that was my favorite muscle car. With anti-sway bars [roll bars] front and rear, the car was as light on its feet as most sports cars. My commute was made a joyful dash in that car.

My 1971 Duster 340 was a bear in a straight line but try a little throttle in a turn and wheelhop off the road. Not a nice car. I pulled out to pass a slow guy going about 40 on my way to work. On a narrow two lane without much in the way of shoulders. Did a 3-1 kickdown, hit a bump and ended up looking him right in the eyes! He refused to move until I was almost out of sight.

As for design, all I can tell you is big valves, a big cam, and a high compression ratio.

Micomlar wrote: “The windage trays supposedly resulted in an approximately 650 to 800 fouth gear top end finish improvement. These trays were also suspected to cause engine damage as they starved some critical bottom end components unless the engine was in peak mechanical shape. I own 3 340s (In a 1972 Challenger, a 1969 Dart and a 1973 Duster) and all 3 had the trays when I rebuilt them. One engine has genuine X heads and the other two have AAWJ 360 with the 1.88 intakes removed and the 2.02 stainless valves and the intake runners worked to match the larger foot print X head gasket outline. By increasing the intake valves and opening up the intake runners, the magic reported answer to the question of how much improvement is approximately 35 ponies. So, with reworked heads and a set of headers, the factory 275 horse animal (that the insurance companies at that time corrected to be 325 horsepower) becomes 330 according to Dodge and 380 horsepower according to the insurance companies. These numbers were 1970/75 numbers, so I am sure with my 750 CFM Double pumper, KB pistons, single plane Weind intake, it’s well over 400 horses! Also, all parts will interchange with all LA blocks, except the crankshafts (and pistons) on the 360s have larger mains. (Heads will need o-ringing). I have put 340 heads on 318s with a stroker kit and ended up with a killer little engine. Also, the 340 and 360s have the beefed up HD rods. The 273 and 318s have the light weight rod versions.”

340 V-8 engine parts identification (Steve Silver)

If you find the J heads at a swap meet, they could be either original 2.02 valve heads (1971) or original 1.88 heads (1972). If you find a set of 1.88 heads and want 2.02 valves, just take them and have them machined for the larger valves.

Some of the 1970 340 Six-Pack engines had heads with a U or O casting letter in addition to the J, but they were still the same part number head (the T/A head had the intake valve pushrod holes drilled in a offset location).

Mike Sealey: T/A engines would be the rare 3x2bbl "340 Six Pack" engines seen only in the Challenger T/A and 'Cuda AAR. I want to describe these as 1970-only engines but I have heard that at least one '71 Challenger T/A was built. These have other mechanical features exclusive to them besides the three deuce carb setup.

Valve covers for 340 engines were different than 318 valve covers. Since the 340 carb was a 4 barrel, it was wider and the carb linkages caused interference with the spark plug wires, so they raised the drivers side wire holder up about 2.5" higher than the 318, to clear the linkages. Also since the 4 barrel carb was wider, it pushed the choke well boss over close to the passenger side valve cover close to the wiring and vacuum advance hose that runs along the valve cover, so they added a rubber coated curved heat shield to the side of the valve cover to protect the wiring. This is how you can tell 340 valve covers from 318 valve covers at a swap meet.

T/A 340 valve covers were almost identical to standard 340 valve covers except the spark plug wire holders were located about an inch farther back toward the rear.

Mopar 340 V-8 Engine - Carburetors

1968-70 - AVS
1971-73 - Thermoquad

Chronology of the Mopar 340 V-8 engine (Stephen Havens)

1968 - 340 released with forged crank, four-barrel carb, hydraulic cam (a more aggressive cam was used in the four-speed cars, just in 1968). New heads, larger ports and valves first year for the dual plain intake four-barrel only
1969 - the four-barrel cars got the same cam as the 1968 automatic-transmission cars
1970 - 340 gets Six-Pak, revised pushrod holes on these J heads for more meat in the intake runners. Also, T/A blocks with thicker webs for the ability to install 4 bolt mains on 2 3 and 4
1972 -
- 318 and 340 compression drops into the 8s
- 340 gets smaller valved J heads (previously all 340 except the six pack got X heads; Six-Pak J heads were machined for larger valves)
1973 - last year for 340, all two-barrel intakes become dual planes with EGR valves; before all intakes were single plane except 340 four-barrel manifolds
1974 - 360 gets the 340 cam, carb, and intake, and is the new high performance small block, in E58 (police) form