building 273..or not

Mopar Performance Issues

  1. Youngthrill

    Youngthrill 69 GT

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    so i plan on beefing up my 69 dart gt 273...i i have a spare 273 i want to start building but i have some questions want to achieve decent hp..im know 273 anrt the best producing motors but hey i have it so ill work with it..

    so ill be using stock crank,it has forged pistons but the block isnt bored and the pistons dont have a dome?? just 4 valve crest's like stock 2b pistons.not sure what thats all about any ideas?

    thinking of comp cams 4'8/4'9 cam lift and like 260 duration...

    i have a original 4 b intake not sure if i should use it or go with a performer...its heavy as hell..and 625cfm demon..the block I'm building is stamped 10-6-66 so I believe its the motor that falls from 66-69 273..the pistons I have I think produce 9.1 ???what came to use for this set up

    is this build worth it...any ideas on hp torque..new to mopar but damn is it addictive...kind of what to do a 273 just for kicks is it worth it..??thanks fabo
     
  2. Djakken

    Djakken Well-Known Member

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    It's worth it.
    I was in the same position, switch 273 with a larger small block, or rebulid? Chose to keep the 273, the reason is that I want something different. I'm in the middle of the rebulid right now. My recipe is as follows:
    - Edelbrock D4B intake, 4 bbl dual plain
    - Edelbrock 1406, 600 cfm intake
    - Comp Cams cam part # 20-246-4, dur @ .015 270/270, 224/224 dur @ .050
    - Electronic ignition
    - Domed pistons, comp. ratio of 10.5:1
    - Spitfire headers
     
  3. BillGrissom

    BillGrissom Well-Known Member

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    The 273 is fun because it can spin faster. Also should give better mpg for a regular driver. It has other advantages in the adjustable rockers and forged crank. Indeed, people use those parts to upgrade later small blocks.

    If you just care about time slips at the drag strip, you would go bigger, but then you go BB and change the entire drive-train, including rear end. Even for a 360 SB, you probably need to upgrade or rebuild the transmission and a bigger rear-end. Even for strictly drag racing, there is more pride in winning with a 273 or even a slant six.
     
  4. Darter6

    Darter6 Well-Known Member

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    Several years ago a guy was racing a 68 4 door dart with a 273. It was street driven and was running in the 12's. Do a search for factory ratings on compression and see the difference between the 2bbl and 4bbl engines. If the bores are good, you may want to use the pistons you have.
     
  5. hemichuck

    hemichuck Well-Known Member

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    The 2 bbl motors had flat tops with 4 valve notches and about 9:1 comp. The 4 barrel motors had domed piston with 10.5 comp. The HiPo's also had a slightly larger cam that was a solid lifter cam.The 1969 motor that you have is Low comp. and has the hydraulic cam so if you want performance your going to start at square one.The early 4 barrel HiPo manifold you have more than likely has a different bolt angle than your motor but the Holley street dominator intake is almost identicle to the old 273 HiPo with the later bolt angle and they are considerably lighter.Your 1969 heads are probably the open chamber versions (like 318's). The early HiPo heads with the odd bolt angle were a closed chamber design.Just a few of the differences to keep in mind.
     
  6. hemichuck

    hemichuck Well-Known Member

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    Another thing to ponder is later 273's had cast cranks like 318's
     
  7. ir3333

    ir3333 Well-Known Member

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    ..sounds like fun
    ..this little engine is low on torque so you will need hi compression pistons and your cam choice will be critical...keep the duration low and be conservative with the lift
    ..a good converter and a tall gear...you'll have to spin it to make power.
    i'm no expert so the advice of a good builder will be critical
     
  8. toolmanmike

    toolmanmike Moderator Staff Member FABO Gold Member

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    Why not build it. They're fun. tmm
     
  9. Youngthrill

    Youngthrill 69 GT

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    I plan on rebuilding the 904 and upgrading to a 8 3/4 with 3.91 gears ...any can suggestions? ??not sure if I should go. 30 over or stay stock any input
     
  10. Djakken

    Djakken Well-Known Member

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    I have the same thoughts, the problem is to find a 8 3 / 4 rear axle with sbp, SureGrip and 3.23 ratio.
     
  11. hemichuck

    hemichuck Well-Known Member

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    You might check the availability of aftermarket pistons before moving forward. If you can find one that you can zero deck thats what makes these motors perk up.
     
  12. 65TerrorCuda

    65TerrorCuda Well-Known Member

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    Stay small on the carb and intake and you will be happier. Electronic ignition and recurved dizzy(faster curve/less mech advance) make a huge difference.
    I switched from 2.7x gears to 3.23's and really didn't notice any seat of the pants difference. Hope this helps

    In hindsight, building a shortblock 318 with the KB399 flattop pistons would be better HP vs $$ but uhhh... less head gasket sealing area? Lol. Too bad those pistons weren't around ten years ago
     
  13. ValiantRacing

    ValiantRacing Well-Known Member

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    273 has forged crank
     
  14. 67valiant 100

    67valiant 100 go fast or go home

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    '68 & '69 had cast cranks, hydo lifters, and single piece rocker shafts. They also never hipo 273 engines those years too.
     
  15. dibbons

    dibbons Well-Known Member

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    The 273 potential is there. I put a 4 speed in a 4 door 1965 Valiant and ran a best E.T. of 12.72 at about 108 MPH. The car weighed about 2960 lbs and used a 4.56 rear end with 10 inch slicks. The other equipment and specs were: bored .060 over (282 CID)with 10.5 pistons (TRW), 312 duration cam with .580 lift (ISKY), Holley 600 CFM double pumper on a Tarantula manifold (Edelbrock), cool can in fuel line, Holley electric fuel pump, Cyclone fenderwell headers, stock heads ported and polished with a dremel tool, bearing clearances set at factory maximums, super stock leaf springs, relocated battery, VW front tires, Chrysler electronic ignition, manual steering and brakes, old orange flex-a-lite competition cooling fan with the stock radiator, and engine components balanced. After a short burnout in plain water (using second gear without a linelock) the car was launched at 6000 RPM and shifted at 6000 RPM with a trap speed on the best runs about 6400 RPM. This was taking place at Fremont Raceway back in the late 1970´s. The car was street legal and street driven until it was sold to the Renteria brothers in 1980 who then spent a few million dollars turning it into the quickest 4 door Valiant in the history of the world. I guess I could consider myself the grandfather of it all, after having purchased the car for $125 with a burned valve back in 1973 or so. Please continue the 273 tradition of blowing away bigger motors.
     
  16. RedFish

    RedFish Well-Known Member

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    My opinion... Build what you already have. If you went out and bought a 318, 360, whatever, the 273 will probably lay somewhere in your way until it goes to scrap.
     
  17. 273

    273 Well-Known Member

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    Dibbons nice 273 it show as long your willing to gear and spin it the potential there.
     
  18. 273

    273 Well-Known Member

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    Dibbons what heads did you run any mods ?
     
  19. seabee

    seabee FABO Gold Member FABO Gold Member

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    I'm in the process of rebuilding my 273, per the guidance of Justin (1wild&crazyguy). It has the eddy performer intake and 1406. Here's the cam sheet and some head pics.
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  20. 72bluNblu

    72bluNblu FABO Gold Member FABO Gold Member

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    Really depends on what you want to do with the car, as has already been mentioned. If you want a strip car the 273 is not your best option, you can make a lot more horsepower for a lot less money with a 318 or 360.

    But, if you want a driver you can get plenty of power out of the 273, and it will get better gas mileage to boot. Most moderate modern rebuilds can get a horse per cube, there's no reason why you couldn't get close to 300 hp out of that 273 and still have a very streetable engine. Up the compression (although I wouldn't go over 10:1 in CA with our fuel), get a more modern cam grind, keep a small port intake like the Street Dominator and a 600 cfm carb, go electronic ignition and get a set of headers. 300 hp in an A body will get you in the low 13's on the 1/4, maybe even the high 12's depending on your set up, traction and driving ability. Plenty of fun for a street car.

    I see you're in Berkeley- if you do decide to build something else, I have a complete, running '74 318 I don't need. Should probably be rebuilt, it smokes a bit on start up because of the valve guides but it was running when it was pulled. I also have a '74 360, complete, partially torn down but all there. Its high mileage with a couple low compression cylinders (rings), but its std and would be a great core. You can PM me if you're interested.
     
  21. 273

    273 Well-Known Member

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    seabee thats a nice cam choice i think you'll be happy just remember go with a little more gear than you would with a larger engine, lots of highway driving 3.23 mixed driving 3.55 intown only 3.91 street strip 4.10's my choice would be 3.91's.
     
  22. joes68340s

    joes68340s Well-Known Member

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    Dibbons I remember your car and still see it around at sac. I also ran a tired but nasty 273. Hipo pistons stock heads, 340 TQ intake and carb, 4.30 gears, auto. I always think about doing it again.
     
  23. dodgetkboy78

    dodgetkboy78 EDELBROCK HEADS SUCK!

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    Seabeas cam is very close to my favorite 273-318 cam from ISKY. 273's love smaller duration, same on both sides cams in the 260* range.

    I can get you my ISKY specs if you so desire.
     
  24. ValiantRacing

    ValiantRacing Well-Known Member

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    Have you seen the harmonic balance on a 68 or 9 273, it does not look like a 360 or am i missing something.
     
  25. OldmanRick

    OldmanRick Well-Known Member

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    360 balancers are larger/thicker because of external balancing....IIRC
     
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