Small Block Mopar Engines

The un-Chevy...

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.

318 Polysphere Engine
318 Polysphere Engine

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...

1964 Plymouth Barracuda
1964 Plymouth Barracuda

(Image: Yzukerman under Creative Commons)

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


Mopar 273 ready to be rebuilt
Mopar 273 ready to be rebuilt

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.

Built 318 Small Block Mopar
Built 318 Small Block Mopar

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.

Small Block Mopar 340 Six Pack
Small Block Mopar 340 Six Pack

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.

Small Block Mopar 360
Small Block Mopar 360

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. How to Rebuild the Small-Block Mopar (S-A Design) 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.

Block Selection

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...

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Please Sign my Guestbook - I appreciate all comments and feedback 13 comments

joanhall profile image

joanhall 6 years ago from Los Angeles

Your lenses are an excellent example of using Squidoo to write about what you know and share your knowledge with like-minded people. Even though I know zilch about cars, I'm giving this lensography an Angel blessing and will feature it on my SquidAngel At Your Service lens.

glenbrook profile image

glenbrook 6 years ago Author

@joanhall: Thanks Joan, I really appreciate it.

mistyblue75605 lm profile image

mistyblue75605 lm 4 years ago

Nice subject. Thanks for the info...squid liked and completed my quest! lol :)P

SoutheastCylinderHead 4 years ago

Good article, you definitely know about MOPAR Engines. The 340 six-pack was an unsung hero on the street racing scene when I was much younger.

anonymous 4 years ago

I have a stock 1990 360 tbi,converted to carberation, 518 trans..It came out of a 1990 dodge ram350 1 ton van lwb. what do you rcomend for a proper fit on the cfm for this engine. we are having tunning diffaculties with an edelbrock 750 (1411). seams to large to us. the chassis is a 1995 ram 1500 ,

glenbrook profile image

glenbrook 4 years ago Author

@anonymous: With stock cam and compression ratio, around 600 cfm would probably work better. What intake manifold are you running?

anonymous 4 years ago

i have a 66 coronet with a factory 2 barrel poly motor,will a factory 4 barrel intake fit with no problems and all intake ports will line up?thks

glenbrook profile image

glenbrook 4 years ago Author

@anonymous: If the 4-bll intake is for the poly 318 it will fit. If it's from an LA engine it won't.

anonymous 4 years ago

@glenbrook: this is what the ad says.i hope hes right!Factory 4 barrel intake manifold for 277, 301, 313, 326 and early (wide block) 318 Mopar engines from 1956 through 1966. These engines are also referred to as a Poly or Polysphere.... thks for the help glockr

anonymous 4 years ago

@glenbrook: and he wants $500 for it!

mowug1776 profile image

mowug1776 4 years ago

great article, I've often wondered about putting a 440 or 426 hemi in 1964 barracuda ( just for kicks). I have two different styles of 318 in.³ one in 1977 Dodge halfton and the other in a 1964 one ton. I also have a 77 half ton with a 360. All three are great engines. At this point I am trying to restore all three so that they are operable. Although I do love the large block Mopar. My 77 with the 318 gets roughly about 20 miles to the gallon highway.

anonymous 4 years ago

How about Poly's

opatoday profile image

opatoday 3 years ago

This is just Amazing Thank You

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