what to do with my 273

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spol46

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I have 67 barracuda with low miles and it has a 273 I want to keep all the numbers matching but want to get some horse power out of the 273. I have most of the externals parts but need some insight on what to do with the internals. Also what kind of power am I going to be looking at.

Or should I store the 273 and just start with a 340.
 
It depends on what your trying to do, if you want to keep the 273 then add the 318 heads as they are a bigger port runner than the 273 and the valve is the same size. Clean up the bowls and do a good valve job and you should be fine. You may want to step the cam up to something in the 220 @ .050 range and .450 lift, this with a 4 bbl and you'll have lots of fun.

BJR Racing
 
I have a 273 in my 67 fastback and it's a great little motor.
I had the heads cleaned-up and put a solid .509 purple shaft cam 292 duration and new springs, the cam is a little big for this stock motor but, it really sounds nice.
it has low first gear 904 trans and 2500 converter ,391 suregrip 8 3/4 , headers,
flowmasters
I give the stock 5.0 Mustangs a run
if you just want somthing to cruise and have fun with and sounds good
 
I sorta wonder the same questions. Although I have a 340 on a stand, collecting parts waiting to be rebuilt, I've found an original date code correct 273 Commando, already rebuilt, for $1000 that would drop right into my car and make my car a numbers matching car! I'm not sure what I want to do now.....

How much horsepower can you expect to get from a 273?
 
I think 300 plus a little isnt hard to get. I'd run the "302" heads, and stay small on the cam. You can then run any later intake. A std Performer would be cool. Paint it, run an AVS, and all the commando stuff.
 
Hey there!
As far as your motor goes, if im not mistaken, the 273 is basically a 318 with a shorter-stroke crank. Going off this assumption (BJR, you seem to be one of the resident gurus around here so correct me if im wrong), if youre really set on making power without an engine swap (which I think is pretty cool btw), you COULD swap in that stroker crank that MP sells for the 318 (basically a 318 crank with the same stroke a 360 crank). There shouldnt be any more block clearancing involved than there is for the 318 & youll make a lot more power without having to run an exotic cam/head. From there, id go with a set of ported 318 heads with the bigger valves. a match-ported Edlebrock Performer intake (I also recommend having the intake runners on the manifold port-matched to each other for equal air velocity as well), top that off with a 700cfm or so vacuum secondary carb, maybe a stock hi po 340 cam or a nice roller (maybe a Comp Cams xteme energy stick) so you can a nice smooth idle (can you say, SLEEPER!) with a converter to match, a good set of long tube headers (NO shorties!) matched up with a good free flowing exhaust. I recommend AT LEAST a dual 2-1/2" set up with a good X pipe (NOT an H pipe, trust me) & a pair of 2 or 3-chamber Flowmasters (depending on how much you wanna advertise. Then, of course, top yer motor off with yer "273 Commando" air cleaner & valve covers & youll have a nice little sleeper there!

A quick note on trannys, I DEFINITELY recommend swapping in a low gearset like Bill P recommended. I did the same on a Duster I used to have & it really made a difference off the line. Plus the torque youll be getting from this motor set up will carry you through the bigger swing between 1st/2nd absolutely NO problems.

For the rear end, 3.55 Sure Grip. nuff said there. Combo that with a set of Cal Trac bars & youll be all smiles as you SMOKE 99% of all the local 5.0s, Camaros & rice burners @ the stop light 500. Plus youll be doing it with 1/4 of the noise & a dead-smooth idle. (imho anyway!)
 
I heard that I could use 360 small valve heads instead of the 318.
 
A 273 block has a stock bore of 3.63", compared to a 318's 3.91" bore. They share the 3.31" stroke, same as the 340. And a forged crank was standard on 273 from '64 thru '69.

I would stick with the smaller 1.78/1.50 valves to reduce shrouding. A pair of 302 swirl port heads and a small port single plane intake like an old Eddy Streetmaster 318 are what I would be looking for. Combine that with a mechancal cam like the purple shaft 276° with .490" lift and it should be a screamer with 3.91 or 4.10 gears.
 
greazerlou and gotdart,
I agree with both of you, but as gotdart has stated they share the same stroke and different bores. I also agree with gotdart as the smaller heads will benifit the littler engine more, but I would use a hyd. cam instead of the mech. type as the torque would be higher due to less overlap.
904s come with a lower gear than 727s stock any way, so this is a plus to start with. The rear gear will just make it that much better. Both have very valid and good points.


BJR Racing
 
what years were the 302 castings made and which cars or trucks would be good boneyard candidates? What would be the best intake that would not have hood clearance problem too? thx.
 
the 273 head is the one to use. it will flow about 158 to 160 CFM @25 " test.
the 302 flows less in the curve vs the 273 head. at .500 302 is little better.
the area from .050 to .400 is where the valve spends most of it's time. this is when the motor needs all the flow it can get. this is on a 920 casting head. the 360 valves are shrouded by the bores, causes flow loss.
 
Or - do what Im doing - drop a 318 in it and hang all the 273 stuff on it. Looks just like a 273, but its 45 ci bigger. My 318 is .060 over so its actually a 328, 55 ci bigger.

Lots of choices on a 318 too. You could put a late model 318 roller hydraulic motor in it or put an earlier 318 in it and run a hydraulic cam in it. Think of a 318 as a small 340, but use the smaller heads. In any event use closed chambered heads to get the CR up. With stock pistons the closed chamber heads give you about 9:1.

Personally if I did it again, I think I'd use the early closed chamber 273 heads refitted with 1.60/1.88 valves, pocket ported, and gasket matched. I used a set of the 302 heads and they'll be fine too, but the intake ports have a huge funky bulge in them from the pushrod, lots of grinding to get that bulge trimmed down. The earlier 273 heads dont have that issue.
 
I'm dropping my 273 for a built-up 318. Going to bag up the 273 because its the orginal motor. I think I'm better off keeping it unless the car got written off or something. Did a rebuild on the 273 so it a pretty good tight motor, besides I would never get my money back from the rebuild....(Cost more to rebuild then the 318 ) :wack:
 
GotDart said:
A 273 block has a stock bore of 3.63", compared to a 318's 3.91" bore. They share the 3.31" stroke, same as the 340. And a forged crank was standard on 273 from '64 thru '69.

I would stick with the smaller 1.78/1.50 valves to reduce shrouding. A pair of 302 swirl port heads and a small port single plane intake like an old Eddy Streetmaster 318 are what I would be looking for. Combine that with a mechancal cam like the purple shaft 276° with .490" lift and it should be a screamer with 3.91 or 4.10 gears.
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IMHO stay way from the 302 swirl ports. My bare bone 273 heads outflow the swirl ports (158 CFM @ .450) Adding a good Stainless valve, bowl blending and back cutting the valves should get me into the high 160's which is plenty for the little 273
 
I also thought that the 65 273 heads were closed chambers, weren't they? Oh, buy they way I'm running a 65 forged 273 crank in my 340 with mallory weight added of course. I wished now that I could of went a stoker crank, but..........

Lee
 
moparlee said:
I also thought that the 65 273 heads were closed chambers, weren't they? Oh, buy they way I'm running a 65 forged 273 crank in my 340 with mallory weight added of course. I wished now that I could of went a stoker crank, but..........

Lee
Click to expand...
They are closed chamber but aren't the intake bolt pattern slightly different on the 64 - 66 heads? I heard that the 67 head is the only head with the closed chamber but has the later style intake bolt pattern, any truth to that?
I put a poly 318 crank in my 340.
 
I'm almost positive that the heads I had were closed chambered and yes it took the first two years intakes cause of the intake bolt angle. Not sure on the 66 and up as far as the closed chamber goes. As far as I now the 66 up took the regular angle intake bolt and had bigger wrench heads on them also.

I think that Mopar Performance and a 318 head with 360 vavles and claim it could make something like 50 horse difference on a 318. Same small port just with a little bigger valves.

I would think that same trick with the 273 closed chamber heads and a zero deck piston would make a killer little 273. I would bet a stock 340 cam with the above sinero(spelling) would be like wow.

Lee
 
My 66 273 has closed chamber heads with the later style intake mounting. I think its the 65 and older heads that had the different intake flange.
 
heres my 65 273,,,,the edelbrock intake is for 64,65,,,,,,also have the 4bbl commando intake for it,,,,hhmmmmmmm,,,which one to run,,,,going in my 66 Valiant Signet convertible commando car

MVC-010S.JPG
 
With that intake I'm sure you'll have to cut a hole in your hood! I'd use the commando intake.

I just threw a pair of '66/67 273 heads in the garbage! I needed the shelf space...I tried to give them away a few times but nobody wanted them. No valve train, just bare heads, I guess they're too expensive to rebuild, anyhow they are landfill now.

I hope I don't wake up one day in the future and realize I need them and find they're going for $500 on ebay!
 
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