little 'ol 273

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six-seven "S"

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I have a '67 Barracuda Form S notchback with the stock 273 Commando, Ed. Performer intake/ Holley 570 St. Avenger, 8 3/4, 3.23, dual exhaust. Just got the go ahead from the boss (wife) to get the engine rebuilt. Anyone have advice on what I could do to add performance? Maybe get up to around 300 hp. Please, don't tell me to get a 360 - I went to a MOPAR guy out here not too long ago, he told me to ditch my engine and couldn't offer any other advice. I would like to keep what I got. Any advice from you guys would be much appreciated..... (I'm pretty new to this stuff, so go easy on me)
 
You could get some liteweight pistons installed at zero deck to raise the comp. A set of 302 heads that are prepped and have a closed chamber for a good quench. And a very good modren cam ground with the small cubes in mind. Headers and a electronic ignition syatem. All the things I planned to do to my 273, but didn't.
These things should get you close to 300 horse.
 
bobscuda67 said:
You could get some liteweight pistons installed at zero deck to raise the comp. A set of 302 heads that are prepped and have a closed chamber for a good quench. And a very good modren cam ground with the small cubes in mind. Headers and a electronic ignition syatem. All the things I planned to do to my 273, but didn't.
These things should get you close to 300 horse.
Click to expand...


Get a 360.:poke: Just joking. LOL

If it were me. I would build it like bobscuda67 said. With mabby a set of 360 1.88-in intake valves and some mild porting work on the 302 heads.

I think it is 85 and up 318 two berrel heads that have hardened valve seats in them allready for unleaded fule.
 
300 hp in a 273 is only 1.1 hp/ci. bobscuda67's adivce should get you close. If you do any port work to the heads it should help alot as well.

I think a Comp Cams XE262H would work well. If you want to stick with a solid cam, the smallest they offer isthe 270S.

I ran the numbers in CamQuest for the 270S

273 0.030 over

flat top pistons, zero deck, 0.040 thick head gasket

302 heads stock flow and valves (flow numbers from Shady Dell Speed Shop which I think are a bit low on the exhaust side becasue they didn't use flow tubes )

9:1 compression with 62 cc combustion chamber (302 heads vary alot but are advertized at around 63 cc)

dual plane high flow intake (e.g. RPM Air Gap) - would need to gasket match heads

500 cfm carb

small tube headers and mufflers

299 hp @ 5500 rpm
325.5 ftlb @ 4000 rpm

the trick will be getting pistons for zero deck build, replacement slugs will be further down the hole and might require more shaved of the heads to get compression up to 9:1 needed for the 270S
 
Does anyone make a off the shelf modern liteweight flatop piston for a 273?
Years ago the only way is to have a set of customs ones made.
 
The only pistons I could find for the 273's is from Egge Machine. I'm sure
the performance piston manufacturers could make a set but hold on to your wallet. Egge does have the low compression and the high compression pistons available. toolmanmike
 
six-seven "S";361250 said:
Thanks fellas. I'm gonna have to print this off and find an interpreter :read2: ..... You guys rock!!!
Click to expand...

Guy who built my 273 use to race stock eliminator with a 65 Dart GT 4 gear car. There's a lot you can do it';s all boils down to money. What are you going to do with the car?
 
I want it to be a street ride with a little bit of balls.... Not planning on taking it to the track or anything like that. Just want to keep the stock appearance and hopefully not spend a ton of cash...
 
I have a 273 in my Valiant, all I did was bolt on a set of magnum heads and put a 455 cam in it, and since it has 1.6 rockers, it made it bigger yet, 4.85 ish if I remember right. Aluminum intake, 600 eddy, and I ran the magnum exhaust manifolds to keep it simple, the thing runs real good, and it was cheap. I just re ringed it along with new bearings, thats all.
I notched the cylinders for the valves, magnums have bigger valves. Dont know if it was needed, but did it anyways, cant hurt.
I bet if I had headers it would really run, but I didnt want the hastle and the ground clearance issues.
Love my 273, wouldnt have it any other way.
 
Just an observation -

One thing about 273 stock pistons - the wrist pins are insanely heavy, compare them to a late model 318. If you dont mind rebalancing the motor I'd look into getting some 318 wrist pins shortened to use with the 273 piston. I suspect mopar used these heavy wrist pins to add weight to the rotating assembly and allow them to get away with using a stock style bob weighted 318 crank. If you did this - it would add alot of rev potential and durability to the motor with very little changes. You would not have to use mallory metal unless I wrong.

I would imagine a cam similar to a 340 stocker might be a good choice - I'd look into getting some higher compression pistons as well. Use the closed chamber heads from the original motor or some #302 castings - you probably dont need to put bigger valves in. If you do, you should probably notch the top of the cylinders to make the best use of the larger valves as well. Definitely a mild bowl porting and port matching for sure on the heads.

Have fun sorting thru these ideas !
 
Looking forward to it! Thanks again. Does anyone happen to know of a good place to get all of this done in Southern Ca.? I can do some basic bolt-on work, but I think I'm gonna leave the rebuild to the Pro's.... (Not to mention, I'm limited on garage space!!)
 
six-seven "S";361338 said:
I want it to be a street ride with a little bit of balls.... Not planning on taking it to the track or anything like that. Just want to keep the stock appearance and hopefully not spend a ton of cash...
Click to expand...

Talked with my buddy and the stock replacement forged piston is made by Ross, part# 57989 and figure on paying $700 - $900 for a set. You are going to pay about the same for the Egge cast piston. Is your motor getting tired? If you are lucky you may get away with a clean-up hone in the cylinders. If you want i'll keep an eye out for a set of TRW forged replacements. Not made anymore but they are out there. Saw two sets at Spring Fling. Buddy of mine bought one of them and the other went quickly. you can always go with the 2 barrel flat top which would give you 8.8CR and with a little head work you could get that 9.1 cr.
 
hi, the stock 920 head will out flow the 302. also, 920 has a closed chamber.
the 273 head responds well to sst nail head valves. also, 920 head has more port velocity, which is needed to fill cylinders faster. you can do some mild bowl blending ,remove all sharp edges, this helps flow greatly!! if so desired, cut down 360 valves to 1.84 and 1.56 diameters. the 920 head responds very good to this size. the360 std size valve doesn't as good have good port velc.
Isky makes avery nice solid lifter cam, grind is the E 4, 260/218 dur, .425 lift, on tight lobe centers, 108 lca. it does work very well in a273!!!
 
I have been working on the 273 setup in my '65 Dart for a while now. Other than the fact that I need to keep the stock engine for class racing, it would be MUCHO cheaper to go to a 318. A 300HP 318 would be easy and you may find one already done. If you decide to do your 273, be prepared to have some pretty deep pockets.
 
+.030 Egge pistons are $340 for the 10.5/1 engine Mike
 
hi, hardened seats are not required. installing sst valves is the answer. if the motor is used in a truck or hauling heavy loads, then yes. another question, how can a 273 cost more?? they use same bearings, gaskets, cam/lifters, timing set, crank, rods, cast pistons cost bout the same!! only difference is bores size.
 
Here's what Mopar did to get 275 hp out of the 273 back in 1966 in the D Dart program.


(from a Mopar tech bulletin)
The "D/Dart" features a modified 273-cubic inch engine with a special four-barrel Holley carburetor. Other features include: A special Camcraft camshaft (284 degrees with .495 intake and .505 exhaust), Racer Brown valve springs, a modified, full-breathing intake manifold, a low-restriction air cleaner, and a Weber clutch. Other standard items are: a heavy-duty 4.86:1 Sure-Grip 8-3/4 inch rear axle, free-flow exhaust headers by Doug of California, a four-speed manual transmission,

I did a rebuild on a '66 Dart Charger 273. Had a very hard time finding the domed pistons in either stock or +.030 sizes. I don't know how well 302 heads will work with domed pistons. The 302 has the smallest combustion chamber of the lot and will not require notching the block for bigger valves.

The original manifold on the 273 4bbl was a single plane cast iron design. It should yeild more top end power. The problem with most aluminum single planes on the aftermarket is they are designed for the larger port heads.

Not sure you can make it to 300 with this motor. Good luck.
 
Man, I didn't expect to get this kind of response to my question... Awesome!! I really need to do more research than I first thought. My pockets aren't too deep, but I'm willing to drop the cash when needed - What do you guys think this will cost me, realistically? I want to make sure that I get the job done right. Also, I heard that the D- Dart was purposely underrated at 275 hp, but was more than likely 300+... Anyone else hear anything about that?
 
perfacar said:
hi, hardened seats are not required. installing sst valves is the answer. if the motor is used in a truck or hauling heavy loads, then yes. another question, how can a 273 cost more?? they use same bearings, gaskets, cam/lifters, timing set, crank, rods, cast pistons cost bout the same!! only difference is bores size.
Click to expand...

Yes, gotta point there. 318 and the 273 are pretty much the same engine except bore.
 
six-seven "S";363539 said:
Man, I didn't expect to get this kind of response to my question... Awesome!! I really need to do more research than I first thought. My pockets aren't too deep, but I'm willing to drop the cash when needed - What do you guys think this will cost me, realistically? I want to make sure that I get the job done right. Also, I heard that the D- Dart was purposely underrated at 275 hp, but was more than likely 300+... Anyone else hear anything about that?
Click to expand...




http://www.seriousviewers.com/D-Dart/ddart.htm
 
When you put all the D/Dart parts on the 273, you might get the extra 40 HP. The D/Dart race teams blueprinted the engines to get the extra HP out of them. The car had headers that went into a special y-pipe that had the header adapters already on it. It also came with 4.86 gears. They ran my D/Dart with 5.30's back in 1966 and were in the high 12's - low 13's at 105.
The D/Darts all had closed chamber 920 heads with 1.87 intakes and 1.50 exhausts. This head was also used on the 1966 w/cap engine. The 920's also came with 1.78 intakes.
 
1967DartGT said:
The advantage of the 302s is the hardened seats.
Click to expand...
advantage after 20+ years? not likely. more advantagous is the Heart shaped chamber, closed chamber, and they have a thicker
deck to allow one to mill the bejesus outta them. theres also the vastly superior exhaust port, and raised roof on the intake
runners.
to the OP,
basically to meet your goals you need 9.5:1 or greater compression, a very good dual plain intake like the LD340 or EdelBrock
Performer RPM ( i wouldn't bother port matching them), BIG CAM.. solid, around 520 lift and at least 286 adv.duration.
holley 750 VAC.SEC. Carb, and 1 5/8ths headers.
with the heads cleanup the runners, put new 1.88/1.50 valves, then port the pocket up to the top cut on the seat. chamfer the
bore on the intake side. this should get you pretty damn close to 300 ]crankshaft horsepower. anything you do above and
beyond this is gravy.
273 are awesome little engines, but you gotta remember it will take alot of RPM to make decent horsepower. or disregaurd everything
and you can just give it a 150hp shot of NOS.. lol!
if yah really wanna freak some minds.. sleeve it, stroke it, and it will still have all the 273 coding on it.
cheers.
 
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