Small Block Mopar Engines
Building a great running small block Mopar is easy - as long as you know what parts to use and have a machine shop that's knowledgeable about the finer points of Mopar power. Running a small block Mopar also makes a statement. Nothing against Chevy, but they're more than a little... overdone. To see what I mean, just go to any big car event - say Hot August Nights. You'll see TONS of Camaros, tons of Tri-Fives, lots of Chevelles and Novas, and most will be powered by the ubiquitous small block Chevy - most likely a 350 with the obligatory Edelbrock dual plane intake and a Holley carb. If it's a really crappy day, you might even see a Ford Mustang or a Plymouth Barracuda "powered" by a small block Chevy (stop for a minute to ponder just how wrong that is). If you want something that really stands out you need a Mopar. If you are thinking about building a Street Machine, don't just go with the flow. Think Small Block Mopar.
Pre-history of the Small Block Mopar
Before there were LA's there was the Polysphere...
In 1967, a 318 version of the LA engine was introduced. It soon replaced the 273 as Chrysler's "bread and butter" V-8 choice. Saddled with low compression and a factory 2 bbl limit for most of it's production span, it never gained a performance reputation. Properly modified, though, it is easily capable of producing 375 to 400 streetable horse power. It also has a well deserved reputation as one of the most reliable engines ever produced.
How to Build Big Inch SB Mopar Engines
In the Beginning - 1964 - birth of the LA-series Mopar small block...
The modern small block Mopar (aka the LA - for Light An engine) was introduced in 1964 with 273 cubic inches and made its debut in the Dodge Dart and Plymouth Valiant. The new LA engine was based on the earlier A engines and most short block components will interchange. The new small block Mopar cylinder heads were quite different though - smaller, lighter, and with a wedge-shaped combustion chamber. The LA engine was about 50 lbs lighter than the earlier A engine and only about 50 lbs heavier than the Mopar Slant Six.
Rebuilding the Small Block Mopar
The Mopar 273
The small block Mopar LA engine family began life in 1964 with 273 c.i., a 2 bbl intake system, and 180 HP. In 1965, a 4 bbl version was introduced. Besides the 4 bbl carb, it also featured higher compression and a hotter cam, producing 235 HP. An even hotter version was available in 1965, producing 245 HP with the help of a solid lifter cam, 700 cfm Holley carb, and factory steel tube headers. In 1966, a special version of the 273 was available in the "D/Dart" producing 275 horse power. No other production Chrysler small block achieved the magical 1 HP/cubic inch - not even the vaunted 340.
Building a Mopar 273 today would almost have to be a labor of love. The main problem with building a 273 is the lack of affordable pistons. A set of cast, low compression pistons for the 273 will cost about $300 if you can even find them (by comparison an equivalent set for a 318 or 360 only runs around $100). An alternative would be custom forgings which cost $800 and up - more than most people would want to spend, especially on an economy type rebuild.
The Mopar 318
In 1967 Mopar introduced an LA small block with 318 cubic inches. The Mopar 318 soon replaced the 273 as Chrysler's "bread and butter" V-8 choice. Unfortunately the 318 was saddled with low compression and a 2 barrel carburetor for most of it's production life, so it never gained a reputation as a performance engine. Properly modified, though, the 318 can easily make 375 to 400 streetable horsepower.
In my opinion, the 318 is the bast all-around small block Mopar. Its small displacement means you can get great gas mileage, but it's big enough to make good power. It also has a well deserved reputation as one of the most reliable V8 engines ever made. If you are looking to build an engine that puts out 300 to 375 horsepower, the 318 is probably your best choice. Cores are easy to find and cheap, aftermarket speed parts are easy to find, and lots of people know how to get good power out of it.
The Mopar 340
The Mopar 340 was introduced in 1968 and instantl became Chrysler's premier performance small block. The 340 came with a 4 barrel carburetor (it was never offered in 2 barrel form), forged steel crankshaft, 10.5:1 compression ratio pistons, and was factory rated at 275 horsepower. It reached its peak of development in 1970 with the 340 Six Pack, a special version featuring 3 Holley 2 barrels mounted on an Edelbrock aluminum intake manifold that made 290 horsepower. The Six Pack only lasted 1 year and was only available on the AAR Cuda and Challenger TA. In 1972, compression was lowered to 8.5:1 with power dropping to 240 horsepower. In 1973 (the last year of production) the forged crank was replaced with a cast piece. The 340 can be built into an excellent performance engine but it's almost impossible to find a good core because of the low production numbers.
The Mopar 360
The Mopar 360 started life as a "smog motor," but after 340 production stopped it took over the small block performance mantle for Chrysler. While it always had potential, it never offered what could be considered excellent performance from the factory. It makes a great foundation for a hot street engine, though. With careful aftermarket parts selection and good building techniques, it can be made into a very strong runner.
Rebuilding a small block Mopar is just as easy as building any other American V8 engine - as long as you have the right information. has everything you need to know about rebuilding small block Mopar engines. It covers both LA series small blocks and the later Magnum engines. If you're rebuilding a small block Mopar, this book is a must-have. How to Rebuild the Small-Block Mopar (S-A Design)
Choosing a solid engine block...
Picking a small block Mopar engine block isn't as easy as other makes. The first thing to consider is engine mounts. The 273 and 318 blocks use different engine mounts than the 340 and 360 blocks. Also, some time in the early 1980s Chrysler changed the engine mount style. If you're running a different year or displacement block than what your car came with, chances are you'll have to buy or fabricate adapter mounts. Not a deal killer, but something to be aware of. The other thing to be aware of is that earlier blocks tend to be cast a little thicker and therefore are a bit stronger. Early blocks can take a 0.030" overbore, but later blocks should be limited to 0.020". I know from experience that the mid-80's and up 318 blocks are prone to cracking between the center head bolt hole and the water jacket. It is an easy repair, but adds about $100 to your machine shop bill. Earlier blocks don't have this problem, and I don't know if the Magnum engines do.
Small Block Mopar Heads
The key to high performance...
Up until the 302 and 308 "high swirl" heads, small block Mopar heads were basically junk - at least for high performance. If you're on a budget, the bast factory LA_style heads are the 302 and 308 castings that came on mid 80's 318s and 360s. Magnum heads work even betterm but you'll also have to change your entire valve train, intake manifold, and valve covers to convert an LA engine to Magnum heads. It would be easier and cheaper to buy a set of aftermarket heads from Indy Cylinder Heads. For an in depth discussion of small block heads, check out the following link...
More by this Author
The Mopar 273 was Chrysler's first LA small block V8. It was introduced in 1964 with a 2-barrel carburetor and made 180 HP.
Building a 318 engine step-by-step with resources, recommendations, and suggestions from experience.
Tips and resources to build a small-block Mopar 360.