Based on the venerable LA design, the 340 remains one of the best small blocks ever built. The LA is the later version of the A design. There, doesn't that explain everything? Okay, let's unravel it a bit. The A was produced from 1955 through 1966, the LA from 1964 on. the LA has thinner block wall castings and head castings. The result was a 50 pound weight savings, as well as smaller dimensions. That meant the LA could easily fit in small cars like the Valiant. It came in 273, 318, 340, and 360 cubic inch versions over the years. Chrysler actually made 3 different 318s over the years, one poly head, one A block, and the LA version. 

When the 340 came out in late 1967, it was engineered for performance and intended to go head to head with the Chevy 327 and Ford small blocks. Separating the 340 from the standard performance 318 were the following differences:

Double roller timing chain 

Oil pan windage tray to improve top end engine RPM by keeping the crank counter weights from churning the oil in the pan. Also, oil didn't slam toward the rear of the pan during hard acceleration and leave the front bearings dry. 

2.02 inch intake valves and 1.60 inch exhaust valves
High rise dual plane intake manifold
Steel crank (until  1973, when a cast iron crank was used)
High performance heads
Revised oil pump with a 90 degree adaptor 

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

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


Valve covers for 340 engines were different than 318 valve covers. Since the 340 carburetor was a 4 barrel,  the linkage caused interference with the spark plug wires, so they raised the driver's side wire holder up about 2.5 inches. Also, since the 4 barrel was wider, it pushed the choke well boss closer to the passenger side  wiring and vacuum advance hose that run along the valve cover.  To protect the wiring, they added a rubber coated curved heat shield to the side of the valve cover.  Generic after market performance valve covers are all lumped together for all 273-360 engines; they all fit, but watch the above details for accurate restorations. 

For the 1970 Six Pack engine, revised pushrod holes on the J heads made more meat in the intake runners. Also, T/A blocks had  thicker webs for the ability to install 4 bolt mains on 2, 3 ,and 4. The 290 horsepower motor also had adjustable rockers with a special hydraulic camshaft with 268 / 276 duration, .430 / .444 lift, "J" heads with  2.20 / 1.60 valves, and  the aluminum Edelbrock intake manifold with 3 Holley carburetors. 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 toward the rear. The correct part numbers for the 340 Six Pack replacement carburetors are: Outboard: P4349239, Center: P4349241. Both are available from Jim's Auto Parts among others. So is the manifold and all associated parts for the fuel system.

In order to race in the Sports Car Club of America's Trans American Sedan Championship, Chrysler  built  street versions of its race cars; these were the Dodge Challenger T/A (Trans Am) and the Barracuda AAR. Although the race cars ran a destroked version of the 340, street versions took the full size 340 and added three Holley two-barrel carburetors on an Edelbrock aluminum intake manifold, creating the 340 Six Pack. The move was obvious; cash in on the success of the bigger 440 Six Pack engines. 

Chrysler rated  the 340 Six Pack at  290 bhp, the same rating as the Camaro Z28 and Boss 302 Mustang.  It actually made about 350 bhp. It breathed air through a large air scoop molded into the pinned, lift off matte black fiberglass hood. Low restriction dual exhausts ran to the stock muffler location under the trunk, then reversed direction to exit in chrome tipped "megaphone" outlets in front of the rear wheels. 

The Torqueflite automatic or Hurst shifter equipped four speed transmission, 3.55:1 or 3.90:1 gears, and a choice of manual or power steering were available. Front disc brakes were standard. The special Rallye suspension used heavy duty parts and increased the camber of the rear springs. The T/A was among the first production vehicles to use different size tires front and rear: E60x15 fronts, and G60x15 in back. The modified camber elevated the tail enough to clear the rear rubber. Side exhaust outlets, thick side stripes, bold ID graphics, and a ducktail spoiler added to the street image. The interior was strictly stock Challenger or Barracuda. 

Unfortunately, the race Challenger T/A wasn't very competitive and the street version suffered from severe understeer in fast corners.  Understeer occurs when  the front tires approach their traction limit more rapidly than the rear tires, the effect being that the front of the car takes a wider radius curve than the driver intended. The T/A would only be available for 1970 as Dodge would pull out of Trans Am racing after one season. The times below are soft pedaled car magazine shake down runs. Well tuned, all out street T/As in capable hands cracked close to 13 flat at 105 mph. 

Even though quality wise the Challengers and Barracudas were pieces of junk with cheap interiors and lots of rattles and a ride that had to be felt to be believed, the T/A and AAR are worth owning. You can fix the factory mistakes like the loose dashboard and cinder block seats if you have the patience and money. A good body man can straighten out the poor panel alignment and give you a good paint job. Some basic changes in the suspension can soften the buckboard ride; a nice set of gas filled shocks is a good start. Let's face it, a short wheelbase car with springs designed to handle almost 400 horsepower ain't gonna win any comfort awards. 

After you correct Chrysler's generic defects, point the beast in a straight line and put your foot to the floor. Hang on, and experience the rush as the high winding 340 slams you into the seat and pins you there. You'll swear you have a 440 or a hemi under your foot, they are just that powerful. I'd take one, and I don't even like E bodies. 

1970 Challenger T/A: 2,142 produced 

T/A: 340+6 V8 290 bhp @ 5000 rpm, 345 lb-ft @ 3400 rpm.

T/A: 0-60 in 5.9 seconds, 1/4 mile in 14.5 seconds @ 99.6 mph.

1970 Cuda AAR  2724 produced

AAR: 340+6 V8 290 bhp @ 5000 rpm, 345 lb-ft @ 3400 rpm.

0-60 miles per hour in 5.8 seconds, 1/4 mile in  14.4 seconds  @ 100 mph.