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The Mopar 273 Small Block

Updated on December 30, 2016
Commando Mopar 273 engine
Commando Mopar 273 engine | Source

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.

Why Build a Mopar 273? - Some good reasons to keep your 273...

In an age when more is better and too much is barely enough, some might ask why 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 happen to think there are some very good reasons to build one.

  • 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 it's 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.
  • 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.
  • Budget Considerations. If you rebuild the 273 you already have, you save the cost of purchasing another core to rebuild. Also, the larger engines won't work well with the smaller intake and exhaust manifolds of the 273, so replacing those would be additional expenses as well. If you're going up to a 360, you'll also need a new torque converter or flywheel, since the 273 is internally balance, while the 360 is externally balanced.

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. Either of these books 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

Things to consider...

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 hypereutectic 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 its 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.

Mopar 273 Piston Availability

In the past, finding affordable pistons for a 273 rebuilt was a challenge. No more. Egge Machine Company has 273 pistons availble in 2 styles, low deck (9:1 compression ratio) and high deck (10.5:1 compression ratio). Prices seem a little high - $428 - but they're the only game in town. Check them out at www.egge.com

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, through 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.

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    • profile image

      anonymous 7 years ago

      I have just purchased a 1968 Dodge Dart out of California, with a 273 ci motor, with the smallest of small transmissions (904) and rear ends (7.25).

      My initial craving was to produce a Hemi looking Dart. Without the high cost of a Hemi.

      Of course I've been searching high and low to replace the complete drive line with a more aggressive small block set-up. But with the recession in full swing, I've been contemplating an expensive build-up with the 273 & 904. Only major change is the rear end. Not much information out there with this build up.

      The limited edition Dart with 275 HP would suit me fine for now. If there are any 273 mopar finatics out there, I would greatly appreciate your imputs.

    • glenbrook profile image
      Author

      glenbrook 7 years ago

      [in reply to Steve ] Your biggest challenge with rebuilding the 273 is going to be finding pistons. If you want to go as fast as possible for the least dollars, a 360 is what you want. Pretty easy to get 450 HP out of a 360 and the core is a lot cheaper than a set of 273 pistons. A built 904 will handle the power OK (it's better than a 727 for racing IMHO), you're right about needing to replace the 7.25 rear end. If you do decide to rebuild the 273... let the rest of us know where you found affordable, quality pistons.

      Cheers,

      glockr

    • glenbrook profile image
      Author

      glenbrook 7 years ago

      Hi Steve,

      Any 360 you find will need some work done if you want to go racing. You don't necessarily need to spend a lot of money. If you read car magazines (esp Mopar-oriented mags) you'll see a fair number of fancy cars with wheel tubs, cages, pimped up engines with big carbs and fender-well headers, etc that only manage to run high 12's in the 1/4 mile. In 2003 (I think) Car Craft put together a budget built 360, stuck it in a 68 Barracuda, and ran 11.70's with it. The important thing is how well your combo works together, not how much money you spend. If I can find the link to the Car Craft article I'll post it here.

    • profile image

      anonymous 7 years ago

      glockr....I haven't fired up my 273 yet so I can't say how my 64 cuda will perform but I can share a couple of things I did...new cam pistons rockers lifters intake and soon exshaust....but the big thing was I put on a set of 318 heads.....bigger valves so it can breath better but even better....less volume then 273 stock heads....with the cam durtation figured in, the math says about 9.5/1 compression......give it enough gas and it should spank that cuda....

    • glenbrook profile image
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      glenbrook 7 years ago

      @anonymous: Hi Michael,

      Where did you get your pistons and what cam are you running? When you get your 64 going hope you'll post on how it runs. I really like the early Barracudas and Valiants.

    • profile image

      BGriz 7 years ago

      glockr,

      I am restoring a 65 Dart GT w/ 273 as a daily driver. I also prefer good mileage and smooth idle. My cam was worn so changed to 0.422/0.444 hydraulic. A little worried too much lift since more than HiPo, but claims "RV/Torque". I now see Rhoades "variable lifters" ($116) that give less lift at low rpm, similar idea to variable valve timing. What do you think? I may try later. I have a Holley Projection w/ O2 feedback and Crane XR700 ignition. It wasn't hard to counter-sink the holes on a later Edlebrock 4-barrel intake to fit. I'll post mileage once I'm driving.

      This is my first small block. I have a Newport w/ 383. I also like the slant 6. I had a 69 Dart 225 for 18 yrs until stolen. Those are sleeper slants on youtube, mostly turboed & some even inter-cooled. A straight six is perfect for turboing. Maybe I'll try that on a slant if I ever get play time. I have a small turbo from a Mercedes diesel.

    • profile image

      anonymous 7 years ago

      I too am rebuilding/restoring the 273 in my 66 Dart this winter. It is an hp motor and I worked to keep as close to stock as possible. The block got a +.030 bore and Egge Machine has both low and high compression pistons. I got the 10.5/1 pop-ups like the originals. I ordered a Isky E-4 cam. It's a solid lifter cam with .260 lift and 425 duration.

      (real close to the stock HP cam) The crank got a .010/.010 turn and the whole thing got balanced. The Egge pistons and pins are lighter than the stockers so a balance was necessary. Most of the short block work has been done and next comes the heads. I have a shop nearby that specializes in Mopar cylinder heads. I will have them go through my heads and port match and bowl blend. They will probably install stainless valves and set them up with new springs. I am going to use the original intake and AFB carb and also the original dual point distributor. My desktop dyno program figured 322 Hp @ 5000 rpm.

      I will be happy if I get over 300 and I would like to dyno it if possible. Mike

    • glenbrook profile image
      Author

      glenbrook 7 years ago

      @anonymous: Hi Mike, thanks for the info on the Egge pistons. I'd looked on their web site last summer and couldn't find the 273 pistons. I went back today and downloaded their latest catalog and sure enough they have them listed. Managed to find them on the web site too. Just might have to get a set. Now I'm glad I held onto my 273.

    • profile image

      anonymous 7 years ago

      glockr I want to correct my post. The E-4 cam is a 260 duration and .425 lift. The Egge pistons are really nice pieces. My machinist was impressed with the quality and consistency. (they were all within .0003 of the same size and very close weight-wise when he balanced them) Mike

    • glenbrook profile image
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      glenbrook 7 years ago

      @anonymous: Hi Mike, thanks for the update and the info on the Egge pistons. I've decided to get a set as soon as I sell some of my Slant Six stuff. Did you get the 9:1 or the 10.5:1 pistons?

    • profile image

      anonymous 7 years ago

      @anonymous: I got the 10.5/1 pistons. I didn't have any ping problems before and hope with ported heads and a fresh rebuild that won't be an issue. I can always use a thicker head gasket if needed. Mike

    • profile image

      anonymous 7 years ago

      I have a 66 f/s , 4 spd baracuda 273, some one has put a egr 4bl manifold on. I understand there is a way to drill the intake to fit the heads, if this is true what's the trick, thanks DB

    • profile image

      anonymous 7 years ago

      @anonymous: The egr manifold is obvilously a late model unit. It doesn't really belong on a 66-273. You need a factory 66 -69 273 intake or an old Edelbrock LD4B. No redrilling is necessary unless you're trying to fit a 64-64 273 intake on 66 and newer heads. Mike

    • profile image

      anonymous 6 years ago

      Hey, thanks for all the info. You mentioned it's difficult to find an aftermarket intake manifold for the 273, but do you know any place where i could get one? the parts for the water hose are thrashed and can't be removed (trust me i've tried).

    • profile image

      anonymous 6 years ago

      offenhauser makes 360* 4 barrel intakes dual plane and most of the non egr inakes will fit with a touch of work i have a 300hp 273 in my dodge truck they will spin up pretty hi and they sound good and pull pretty hard with a decient cam i can't remember what cam i have in mine i think it is a isky the motor is out of a 65' dart has minor port work 30 over and the later model truck rods for more strength and biger rod bolts the 273 also came stock with adjustable valve train they run cooler and have thicker cylinder walls i pull mine to almost 7 grand a lot it is a good motor and is different everybody kind of gives me a look when i tell them i have a 273 instead of a 318 or 360. also check paw and cambell enterprises they have a lot of nice mopar stuff also try enginekits.com for pistons and as always wiesco will make a piston for anything a resonable price but unless your boosting of spraying your engine cast piston will do just fine. im glad to see other people running 273's hope yall have good luck with yours

    • profile image

      anonymous 6 years ago

      @anonymous: u can also swap on late model magnum heads it pretty easy u have to swap out lifters and pushrods and head gaskets but u get 160-190cc runners depending if rt's or just magnums and 60 cc chambers and a lot better valve covers and valve train and with the new gas u can run a little more compression and more fuel and if u run a carter/edlbrock u should put a phernolic spacer to help against hydrolocking cuz this ethenal gas is a nightmere on the old stuff and remember if your running pre 74 heads the werwe designed for leaded gas and u need to install hardend seats or they can get beat up and come out of the pocket and trash a good motor quick

    • profile image

      anonymous 6 years ago

      @anonymous: Offenhauser has 64-65 4-barrel intakes. Otherwise look on e-bay or hang around forabodiesonly.com and ask if anyone has one. They surface from time to time. toolmanmike

    • profile image

      anonymous 6 years ago

      Just an update. My HP 273 is in and burnin' gas. It runs good with just a few hundred break in miles ion it. I am fighting carb problems. The original carb has sloppy throttle shafts and is causing vacuum leaks. Otherwise it runs pretty strong. Mike Weidner Here's a link to my build. http://www.forabodiesonly.com/mopar/showthread.php...

    • aka-rms profile image

      Robin S 6 years ago from USA

      Great info!

    • Andy-Po profile image

      Andy 6 years ago from London, England

      Excellent lens. Very interesting. I wish I had more time to work on my cars' engines.

    • profile image

      anonymous 5 years ago

      a great carb option is a rochester 375...right off a old pontiac...you'll almost think you have a 4barrel. this is an old hot rodders swap that i have seen a few times and was always impressed. it will also help with the commen cold natured aspect of start ups

    • profile image

      anonymous 5 years ago

      My 68 dodge Coronet 500 runs a LA 273 engine, so far the best ride car I ever had,

      very enjoyable car to ride,smooth and fun driver,not to mention very reliable engine.

      Long live for the 273 dodge engine if you have one keep it.

      if i want a loud ride I just take out my 71 b body 440

    • profile image

      anonymous 4 years ago

      Ok I have a 273 2 barrel on my 67 dart I want to go up to a four.barrel and have had a time finding the.intake manifold if I buy an original 67 4 barrel intake will it fit right on the block no problem?

    • profile image

      anonymous 4 years ago

      @anonymous: 273, 318, 340 are all LA motor so the intake for any of these motor will fit. There are a number of after market intake that will work also. Edelbrock come to mide. There RPM preformer for small block will work fine for your aplication

    • profile image

      antoniow 4 years ago

      Interesting lens, well done!

    • profile image

      anonymous 4 years ago

      @anonymous: Actually, the 340/360 had larger ports. The Performer RPM will not work well on a 273/318 out of the box. You really should do your research before giving out bad advice.

    • profile image

      anonymous 4 years ago

      @anonymous: I guess if old hot rodders = cars under 100 RWHP. Anytime I hear "old hot rodders trick" I cringe - it typically comes from people that haven't done it, heard it from somebody their cousin's brother's wife's sister's daddy knows, etc.

    • glenbrook profile image
      Author

      glenbrook 4 years ago

      @anonymous: That's correct - putting a manifold designed for the 340/360 heads onto 273/318 heads creates a "step" where the large port on the manifold connects to the small port on the head. This kills intake flow and hurts performance. I'll also add that I don't think it's a good idea to run the 340/360 heads on the 273 or 318. The larger ports on those heads don't have good intake velocity on the smaller engines so low rpm torque really suffers.

    • glenbrook profile image
      Author

      glenbrook 4 years ago

      @glenbrook: One more thing - I think the best intake for the 273/318 engines is the Weiand Action Plus. It's a nice high rise dual plane with ports that are the correct size for the 273/318 heads. A regular Performer (not RPM) also matches the small port heads.

    • profile image

      anonymous 4 years ago

      I,m changing a 273 with a 383 (sold to me that way) is the engine cradel and motor mounts a problem if so how to do it

    • glenbrook profile image
      Author

      glenbrook 4 years ago

      @anonymous: It depends - if it's a B or C body you should be able to get factory mounts for the 383. If it's an A body you might need to get something fabricated but the engine should fit fairly easily. If it's a 63-66 A body you might have problems. In those cars a small block barely fits.

      You'll also need a new transmission (if it's an automatic) or bell because the bolt pattern is different between the small block and big block Mopars. If you have a 7-1/4 rear end in the car it might not last very long behind a big block so it would be a good idea to upgrade that too.

    • profile image

      anonymous 4 years ago

      @anonymous: how do i check the rearend to see what package i have

    • profile image

      anonymous 4 years ago

      @glenbrook: Hi Glocker. I have a 1966 barracuda with the 273 engine and can't seem to find the Weiand intakes for a 273. I see them at summit racing for the 318. Wonder if it will fit. How would I find out if it would fit?

    • glenbrook profile image
      Author

      glenbrook 4 years ago

      @anonymous: @Sheeza66... I have the intake off my 318 right now so later this week I'll set it on the 273 and see what doesn't line up and let you know. I _think_ the only difference is the bolt angle... if so all you'd need to do is spot-face the manifold so the bolts mate correctly. Probably cheaper than buying an intake made for the early 273 and you also get a better manifold.

    • profile image

      anonymous 4 years ago

      I'm rebuilding my 273 ,bored .030 over ,found pistons and gaskets ,cam bearings ,everything I need but it got pretty expensive. But I'v got a 65 barracuda. Anyway I got it about finished ,but we can't find the rocker arm assembly. Now I have to spend money to replace it Its hard to find with solid lifters. I'm trying to find out if the rocker assembly from a 318 will work in place of the 273 rocker assembly.

    • profile image

      anonymous 4 years ago

      will the 318 rocker arm assembly work on the 273

    • glenbrook profile image
      Author

      glenbrook 4 years ago

      @anonymous: The 318 rocker arms aren't adjustable so they won't work with a solid lifter cam. It would probably be cheaper to buy a hydraulic cam than it would be to buy adjustable lifters and matching push rods.

    • profile image

      anonymous 4 years ago

      @anonymous: Ron, If you need 273 parts, there's a large 273 following on forabodiesonly.com

      You should be able to find what you need there. toolmanmike

    • glenbrook profile image
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      glenbrook 4 years ago

      @anonymous: Thanks for the tip Mike. My comments section won't allow html but I put a link just above.

    • profile image

      ChickenGutz 4 years ago

      Great and informative too. Thanks

    • profile image

      anonymous 4 years ago

      I had the thought of stroking the 273 to 300 or 302 with the 3.58 stroke crank from a 360 and using 302 casting or magnum heads and a little boost super or turbo try that on for size

    • profile image

      anonymous 4 years ago

      @anonymous: I know this is an old post, but also know finding parts can take a long time. I have a 273 D4B Edelbrock aluminum hi-rise manifold that will work on your motor. I believe the bolt holes have been elongated to fit the newer heads but can easily done if not. This manifold fits the early 273's because of the bolt angle change. You can reach me at: hweinberg1212@comcast.net

    • profile image

      anonymous 3 years ago

      @anonymous: nick g

      I have a edlebrock high rise manifold with a edlebrock 4 barrel carb and chrome air cleaner that came off a 273 1966 valiant that will fit your dart.

    • profile image

      anonymous 3 years ago

      @glenbrook: In addition to the 340/360 ports being too big, the combustion chambers are too big and the block has to be ground (clearanced) so that the intake valves won't hit. The 273 heads are closed chambered heads and are very efficient for the bore size. They can be port matched and the bowls cleaned up for more flow. Check out my 273 build thread. Just Google " toolmanmike 273 build thread".

    • profile image

      anonymous 3 years ago

      Just a correction on your opening statement. In 65 the HP273 was introduced with 235 hp etc,etc. Plymouth called it Commando 273 and Dodge called it Charger 273. In 66 there was a 275 horse version of the 273 available in the Dodge line only. It was only available in the D Dart and was a factory built car to compete in the NHRA D-Stock classes. toolmanmike

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