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The Mopar 273 Small Block - Should You Build One?

Glenbrook is an online mechanics writer, who enjoys rebuilding and modding classic Chrysler cars.

Chrysler 273 LA Small Block

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. In 1965, a high-performance version called the Commando was introduced. The 273 Commando had a hotter cam, 4 barrel carb, and made 235 HP. In 1966, a limited-edition racing version of the 273 called the Super Commando was offered. The Super Commando was equipped with steel tube headers, a 700 cfm Holley 4-barrel carburetor, a high lift mechanical camshaft, and made 275 HP. Production of the 273 spanned 6 years, lasting through the 1969 model year. The low-end version was replaced by the Mopar 318, while high output versions were replaced by the Mopar 340.

The engine in the picture below is the 2-bbl version of the 273 in my 66 Plymouth Barracuda. I wasn't sure what to do with it since I'm replacing it with a 318. The more I think about it, the more I want to rebuild it. In spite of the small size, the Mopar 273 is a good engine. As the first engine in the LA series, it's also an important piece of Mopar history.

Who In Their Right Mind Would Build a Mopar 273?

In an age when more is better and too much is barely enough, some might ask why they should even bother with a 273. Even a lowly Mopar 318 adds 45 extra cubic inches, and it's easy and fairly cheap to build a small-block Mopar all the way up to 408 cubic inches. So why bother with a 273? I can think of two reasons - (1) your car came with a 273 and you want to keep it original, or (2) you want something different.

  • Keeping it Original. If you have a 273, chances are it's what your car has as original equipment. Whether you feel keeping your car original increases its value, or you just like the idea of keeping it as the factory intended, a 273 can provide good performance and economy. Aftermarket intake manifolds that fit the early versions of the Mopar 273 are difficult to find, but if your intention is to keep it original, that won't be an issue for you.
  • Something Different. If you're building a Mopar 273 just to have something different, it can be done. Keep in mind that it's going to be expensive, and the small bore size of the Mopar 273 really restricts the intake valve size, which in turn really cripples the performance potential of the littlest small block Mopar.
  • Fuel Economy. Since the Mopar 273 is the smallest member of the Chrysler LA family, it also has the best fuel economy potential. The 318 has an excellent reputation for fuel economy, and since the 273 is 14% smaller, it should be able to get even better fuel economy than the 318. If you try this, I'd recommend replacing the stock 273 heads with late-model 318 high swirl ("308") heads.

Rebuilding a Mopar 273

To Rebuild Your 273 You'll Need Correct Specs and Information...

Rebuilding a Mopar 273 isn't difficult... IF you have the correct information. You can find many books that will provide you with the specifications and techniques you will need to rebuild your Mopar 273 or any of the LA Series small block Mopars.

Challenges to Building a 273

If you decide to build a 273 Mopar, there are a couple of challenges you'll face. Egge Machine has solved the piston availability problem for the 273 - if you don't mind running cast pistons. Also, at around $300 a set, the Egge 273 pistons cost about 3 times as much as a set of equivalent TRW pistons for a 318 or 360. If you want to go high-end, Ross will make you a beautiful set of custom forgings, but the almost $900 they charge is an awful lot to spend on a 273. If you want to run hyper eutectic pistons in your 273, you're out of luck because they aren't available for the Mopar 273.

The second challenge is developing power in a performance application. The 273 can definitely make good power - the problem is that because of the small displacement you have to spin it really fast to get there. Also, the small bore size restricts the valve sizes you can run, which in turn limits the flow of air into the engine, which in turn limits the amount of power the engine will make. Does this mean that building a 273 is a waste of time and money? Not hardly, you just need to be aware of what you're getting into if you decide to build one.

Economy with Performance: Where a 273 Can Really Shine

Not every car needs to be a street racer. When I was in high school, my sister had a 65 Mustang with a 200 inline six that could burn the tires at will. My 64 Valiant station wagon with its 225 Slant Six also performs OK for a driver and gets good mileage as well. The 273 Mopar is quite a bit bigger than either of the sixes I've driven and should offer excellent performance in the right car. It's also quite a bit smaller than the next-in-line Mopar V8, so it should be able to deliver excellent economy as well.

My Mopar 273 Experiment

Never let a good engine go to waste...

I just picked up my 273 from the shop that is installing my new 318 and handling the 5 speed conversion on my 66 Barracuda. I've been trying to decide what to do with it - strip it for parts (the 273 has a forged crank that will fit a 318), try to sell it, or throw it away... In the end, I decided to keep it. My garage space is limited though, and I can't afford the luxury or storage space of just keeping something for the sake of keeping it. So I'm going to rebuild it - if it can be rebuilt. The valley looks horrible. Lots of black gunk like maybe it never had an oil change. I'm not sure about the bores, either. I am, however, an optimist. I got it mounted on a stand today and will start evaluating it over the next week (my wife is out of town, so what better way to spend quality time in my Man Cave?).

Assuming it's rebuildable, the only challenge would be finding affordable pistons. Both Summit Racing and Performance Automotive Warehouse list Mopar 273 pistons. Summit's ever-shifting "estimated ship date" is currently listed as November 13, and I haven't called P.A.W. yet to see if they have them in stock. If I can find pistons and the block will clean up with a 0.030" bore though, I'm going to do it. It will be a performance with economy build, with the emphasis on economy. That means I'll be reusing as many of the stock parts as possible, including the cylinder heads.

Using the stock heads throws another twist into the mix. These are early-style LA heads, so current aftermarket intake manifolds won't fit without modification. So... my choices are to see what I can do with the stock two-barrel manifold or modify a modern four-barrel manifold to fit the heads. Either choice is interesting to me. I have a Holley 350 cfm 2 bbl that I've been dying to try on something, so that option would be fun. OTOH, it would also be fun to see what kind of improvement (for both power and economy) could be gained by upgrading to a modern 4 bbl manifold and carburetor.

More Information

Probably the best place to get more info on the 273 is at For A Bodies Only. They have a great tech section in their forum and lots of knowledgeable 273 fans.

Performance With Economy - Getting Performance AND Economy From your 273

This book is out of print, but it is still available from several resellers through Amazon. If you work on older cars and care about both performance AND economy it is well worth your time to hunt down a copy of this book. I have a copy of this book and it is probably one of the top 3 books I own in terms of how useful it is. It's also written in a very easy-to-understand style with clear examples. Some of the information is a little dated but most of it is still very relevant today if you're working on an older (carbureted) car.

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.