72 slant six upgrade

Slant 6 Engines

  1. dragonrider

    dragonrider Active Member

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    I have a stock motor and I am wanting to upgrade/improve the motor. One for better performance and 2 for better gas mileage. It has stock points which I am going to totally switch out to electronic. Then come the intake upgrade....? Without having to switch cams and do headwork.... I was going to go with the offy 4 or the Offenhauser Dual Carburetor Intake Manifolds 5041 series which runs 2 1 barrel carbs. BUT I have not had anyone give their thoughts about it. I will add headers at a later date with 2.5 pipe and an X pipe added. But for now the ignition and intake carb set up are my questions. Any thoughts???
     
  2. dragonrider

    dragonrider Active Member

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    forgot to add that this an automatic.
     
  3. RustyRatRod

    RustyRatRod Bla de blizhibliz de blatde blizi bla bla FABO Gold Member

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    If you do all that, do it for the cool factor. You won't add a substantial amount of power or increase mileage dramatically.
     
  4. CultClassik

    CultClassik Well-Known Member

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    Agree, and I'd bet you'll get worse mileage with anything but a 1bbl carb, but I've never tried. If you're set on keeping the six, factory elec ignition is cheap and will be better than points at least.
     
  5. sargentrs

    sargentrs Well-Known Member

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    I'm getting 20mpg with my 225 /6. All I've really done is replace the carb with a stock Holley 1945 (reman) and swap to GM HEI electronic ignition. That and a good tune up and fine tuning the timing and carb.
     
  6. Dustert73

    Dustert73 Stripping bolts since ‘10

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    Never ran a offy dual carb setup, but that setup looks great on a slant with the right air cleaners.
     
  7. RustyRatRod

    RustyRatRod Bla de blizhibliz de blatde blizi bla bla FABO Gold Member

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    And that's around the best they will get give or take about 5MPG. There are those that say "my slant gets 30 blah blah blah" but either they are stretching the truth or they don't know the correct way to measure mileage. There was really only one package that got that kind of mileage from a slant. Those were the "light" cars. The Feather Duster and the Dart Light. They came with aluminum and lightened body panels and 4 speed OD transmissions. The automatic equipped cars got around 25.
     
  8. Badvert65

    Badvert65 Long Time Mopar Nut

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    The dual carb intake (at least the one I have) does not have a provision to bolt to the exhaust manifold. You would either need a header or cap off the factory exhaust manifold. I haven't installed my dual carb manifold as I am going to modify it to run dual two barrel carbs instead of the one barrel ones.
    -Matt
     
  9. dragonrider

    dragonrider Active Member

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    Thanks for the help. My one barrel is sucking the gas, so thinking the better the breathing the better the gas mileage? As a 4 gets better than a 2, as long as you stay out of it. Then a 4 should be better than a 1? and with headers that would also help?
     
  10. Princess Valiant

    Princess Valiant Duster specialist FABO Gold Member

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    wow ....that is great mileage....I am getting 16 MPG in a 68 dart with 225/833 OD and 2.76 open. with electronic ignition upgrade from a 75 dart sport.

    I think the engine has never been apart but still does not use oil. I have been told that I might be a lead foot too.

    But 16 is the absolute best I have recorded to date. :???:
     
  11. nm9stheham

    nm9stheham Well-Known Member

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    No, not really any correlation between carb barrel numbers and mileage. The Dart Lite's and Plymouth Feather Duster's got the high 20's on the interstate at 70 mph with a 1 BBL carb (with the manual trans); I know since I drove one for most of a quarter million miles. Better gas mileage for a given throttle setting and speed is a matter of better combustion efficiency, lower engine losses, and/or fuel mixture. This can be due to:
    - Better fuel-air mixing due to a lot of factors
    - Better fuel-air distribution due to a variety of factors
    - Leaner fuel-air mixture at the most common driving RPM's
    - Lower engine speed due to different gear or trannie (the Lites and Fethers Dusters had a 4 speed overdrive manual trans); that lowers the engine RPM's and that lowers the engine pumping losses
    - Larger exhaust improves exhausting the spent gases and makes the combustion cleaner and more efficient; it also helps cylinder filling which helps power.

    I would not expect better mileage with a larger carb but it all depends on the carb and a bunch of other things. Your 1 BBL sucking the gas means either the 1 BBL has a problem (that can very likley be fixed) or you have a heavy foot.
     
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    • Badvert65

      Badvert65 Long Time Mopar Nut

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      My 79 Volare wagon (super six automatic w/2.91 gears) got 30 highway mpg. It was a slug, but got great mileage.
      -Matt
       
    • dragonrider

      dragonrider Active Member

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      The carb does have some problems as well as the ignition. Once it get the ignition upgrade done I will work on the carb problem. I USED to have a lead foot but that was with my 72 charger S/E with a 440 mag and slapstick. ....LOL
       
    • bigus1949

      bigus1949 Well-Known Member

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      dragonrider. a few pics of the swinger
       

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    • bigus1949

      bigus1949 Well-Known Member

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      J C Whitney has the /6 intakes
       
    • bigus1949

      bigus1949 Well-Known Member

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      the /6 headers are on the binghamton, ny craigslist
       
    • Veryfastdart

      Veryfastdart FABO Gold Member FABO Gold Member

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      Figures
      I just bought a car there last week!
       
    • CichliDart

      CichliDart Well, where is it now?

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      I am fairly sure they do not carry them anymore. They no longer list them on their site and I recall reading here on FABO that JCW had a closeout sale and a lot of members scored them.

      There is always FABO and ebay.

      At the moment ebay has the Aussie 2 and 4 bbl intakes, an M1 2 bbl(factory), a two 1 barrel intake, and an Offy 4 bbl intake.

      Also a 1 barrel intake with draw through turbo set up.
       
    • RustyRatRod

      RustyRatRod Bla de blizhibliz de blatde blizi bla bla FABO Gold Member

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      No. It doesn't. You're doin it wrong.
       
    • 65 Dartman

      65 Dartman FABO Gold Member FABO Gold Member

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      If it's an Offy dual one barrel, it will bolt to a stock manifold.
       
    • dragonrider

      dragonrider Active Member

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      nice car and a very clean engine. I will look into the headers at that price.
       
    • dragonrider

      dragonrider Active Member

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      are you going to be running the Clifford set up? With the webers and headers.
       
    • a12

      a12 Well-Known Member

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      I appreciate your honesty :burnout:
       
    • Darter6

      Darter6 Well-Known Member

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      I agree with Rusty,driving slants from the 60's to present day one thing they were never known for was for fuel mileage. Most averaged 14 to 16 on a good day.Flat land areas may have gotten better.Rear axle ratio makes a difference.Talking A bodies early slant cars with 170 engines usually had 3.23 gears.225's on the average had 2.93.Depending on the terrain you drive you need to gear for those conditions. For me out west roads are mainly flat with speed limits in the 65-75 range .I've gone with 2.76 with great results being a max of 20 mpg for the roads traveled around here.Any engine will benefit from better breathing in and out.
      So the question is what is the condition of your engine.? First check compression, if the cylinders vary more than 25 psi you may be chasing your tail looking for performance and better fuel economy.
      If you find it to be healthy,Then a intake and exhaust change will help you to reach your goal.Along with a good tune including valve adjustment. Have fun with your project and thanks for wanting to work your slant.
       
    • Jeff Lemon

      Jeff Lemon Well-Known Member

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      Rusty is correct . I added Clifford intake, headers , 390 Cfm Holley and total electonic ing. and a Dist. built by Johnny Dart from Cal. he is on this site. Yes it is a little faster but very smooth and fun. Used Lokar linkages and 2.5 single exhaust with a flowmaster. Johnny Darts Dist. was an outstanding addition just smoothed out everything.
       
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