The 340: Classic Mopar Performance in a small package
When it comes to Mopar engines built during the muscle car era, most of the attention is focused on the legendary big blocks and the iconic Hemi. Let’s talk about small blocks. Chrysler small-block performance really got its start with the release of the “LA” series in 1964. Although the venerable 318 “A” engine had been around since 1957, it was simply a workhorse V8 with very few performance pretensions. With the LA engine, Chrysler had its first modern “thinwall” V8. Debuting in 273 cubic-inch form, the engine was installed in the small A-body series of cars such as the Valiant and early Barracuda. The solid-cammed, 4-bbl 273 in the ‘66 Barracuda Formula S made 235 horsepower which was certainly respectable and fun in the lightweight car. The serious small-block performance, though, arrived with the 340 in 1968.
The 340 was designed from the outset as a performance engine. From the forged-steel crankshaft and connecting rods (which were also shot-peened by the factory for stress-relief), to the big-valve (2.02” intake, 1.60” exhaust) free-flowing heads, the 340 was built to run hard and live doing it. The ‘68 edition made 275 horsepower with a single 4-bbl Carter carburetor.
Chrysler’s 340 reached its highest state of tune in 1970 with the famous 340-6 bbl engine. Designed for use in the popular and hotly contested SCCA Trans-Am racing series in the Plymouth AAR ‘Cuda and Dodge Challenger T/A, the engine’s most striking feature was the use of three 2-bbl Holley carburetors on an aluminum intake manifold. Chrysler engineers designed a special block for the AAR/TA engine which featured extra-thick main webbing to allow for 4-bolt main bearing caps. The previously mentioned forged crank, rods and pistons were carried over. Compression remained at 10.5:1, while the hydraulic camshaft was also the same (.430” intake, .445” exhaust) grind used in the standard 340. The cylinder heads had special, widened intake ports that were made possible by relocating the intake pushrods. Another unique aspect of the AAR/TA 340 was a fully adjustable valvetrain, with 2.02” intake and 1.60” exhaust valves. Chrysler severely underrated this screamer at 290 horsepower. This was, not coincidentally, the same rating applied to Chevy’s Z/28 302 and Ford’s Boss 302, both of which were also Trans-Am “specials”. In competition form and destroked to the SCCA-mandated 305 cubic inches, the AAR/TA engine produced around 440 horsepower.
The bean-counters got to the later versions of the 340. While the engines still made good power, some of the components weren’t quite as strong as on earlier models. Of course, this made them less expensive to produce, and the manufacturers were starting to see the writing on the wall with respect to emissions and insurance regulations. The 360 replaced the venerable 340 in 1974, and actually made use of many of the 340s components.
Mopar’s 340 is one of the all-time great small block engines. In a nice, light A-body with a 4-speed, the screamer small-block would humble some of the best-known big-inch muscle cars of the day – which makes the 340 one of the legends of the muscle car era.
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