Chryslers Classic 340 Small Block V8

1970 Dodge 340 Cubic Inch V-8
1970 Dodge 340 Cubic Inch V-8. Photo by Mark Gittelman

In the mid 1960s Chrysler identified the need for a high performance small block engine. The 1963 Chevrolet Corvette 327 Fuelie engine produced 375 HP. Chrysler's 273 Commando V-8 and the 318 cubic inch small block weren't ready to challenge the Chevy's on the street.

This is unfortunate, because Dodge and Plymouth had several light weight, compact cars in the lineup. The Dodge Dart Swinger and the Plymouth Barracuda needed something small and powerful under the hood.

Here we'll talk about one of Chrysler's most successful V-8 engines of all time. Discover the first year for the classic 340 CID V-8. Find out why this engine is much more than a bored out 318. Review compression ratios, carburetor options and advertised horsepower ratings.

First Year for the 340

By the middle of 1967 Chrysler's Mound Road engine assembly plant in Detroit, Michigan started cranking out the 5.6 L 340 CID V-8. These completed power plants would find their way into the new 1968 models coming out in September 1967. The factory rated the first engines coming off the line at 275 HP at 5,000 RPMs. You could gain another 15 HP by selecting the 3 two barrel carburetor options, known as the six pack. This is quite a step up from the previous year’s 318 rated at 200 HP at 4,400 RPMs.

The Last Year for the 340

After a six year run Chrysler pulled the plug on the 340. Officially 1973 was the last year they mass-produced the engine.

However, the replacement 360 CID motor had a special performance version in 1974. The parts that made it high performance turned out to be leftovers of the 340 build. The cylinder heads and high-rise dual plane intake manifold allowed the 5.9 L 360 to achieve reasonable performance. Dodge installed a few of these left over performance motors in the Lil Red Dodge Express pick-up truck.

340 V-8 What's Inside

Let's start from the bottom end and work our way up. In 1968 and 1969 the 340 used a forged steel crankshaft. The 273 Commando and 318 LA series before it used a cast-iron unit. Chrysler also utilized forged connecting rods to help hold the engine together up to its new 5,000 RPM red line. A High lift camshaft is rotated by a standard double roller timing chain and gear set. They also upgraded the push rods to forged components.

Many believe it's the cylinder heads that really made the difference in this engine. High flow heads with large 2.02 intake valves facilitated the use of large CFM carburetors. Another major difference between the 60s engines and the ones built in the 70s is the compression ratio. With increasing emission regulation and the elimination of leaded fuels, compression began to drop in 1970. In fact, it would fall from 10.5 to 1 in 1968 and 1969 to a miserable 8.5 to 1 for the 1972 model year.

My Thoughts about 340 Engines

Throwing out horsepower numbers rated by the factory in the late 60s and early 70s should be taken with a grain of salt. On the street, a Dodge Dart with a 340 can hold its own against a third generation Chevy Nova Super Sport with a 350 HP 327.

The cars weigh in at virtually the same curb weight. Yet the Nova has no real advantage despite its 75 HP advantage on paper.

My first car was a third generation Dodge Charger. It came with a 318 two barrel rated at 180 HP. It ran a despicable 17.5 second quarter-mile. I replaced the worn out engine with a 360 CID police interceptor engine. Nevertheless, the car still ran in the low 17 second range. After a couple of years of driving the car up and back to school I began project 340.

I rebuilt a 1969 340 V-8 with factory original parts. I never had the car tested on a dynamometer, but expected results near the factory 275 HP rating. The first run yielded a 14.50 in the quarter-mile. I later got the car to break into the 13 second window by adding a Mopar 8 3/4 rear differential with a 3:55 gear ratio.

For me the lesson learned is, if you want to go fast with a Mopar small block, don't waste your time with anything except the 340.