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70 BARRACUDA HIGH RPM @HWY SPEED

Transmission and Drivetrain

  1. temsinc

    temsinc Member

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    I have a numbers matching 70 Barracuda, 318 w/mild cam, Edelbrock 650cfm 4 barrel carb, Edelbrock RPM Air Gap intake, 340 Aluminum Heads, 905 AT. She's a little torque monster but I am having a few issues:

    1. Can't seem to dial in the carb, its brand new and has never ran correct. It falls flat when I put my foot into it, got to feather the accelerator to make her go. Im considering converting it to EFI with the Fitech 30003.

    2. Secondly, I find that at low RPM, I loose my brakes most likely due to low vacuum from the mild cam. Looking at possibly going to a hydroboost kit.

    3. At 3000rpm I barreling down the Hwy at 60mph. Any suggestions?
     
  2. tonysrt

    tonysrt Well-Known Member

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    Did you check timing? Make sure your getting full advance. If you have a manifold leak you'll never get it running right. Is this a motor with just those parts installed? Motor ran OK prior to parts installation? If so then retrace your parts installation. I put a 4bbl manifold and 1406 Carb and engine ran terrible. I thought it was Manifold leak but when I took it apart found all pushrods bent and distributor advance plate was loose. Fixed those 2 problems and stock 318 runs great.
     
  3. Adam

    Adam Well-Known Member

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    Try adjusting the accelerator pump for more squirt...

    A mild cam should still have enough vacuum for brakes. Put a vac gauge on your eng and take a reading. I agree with tonysrt, probably a vacuum leak around the manifold, vacuum hose to booster, or internal booster. Spray small amounts of carb cleaner around the edges of the manifold, valley corners, etc. while idling and listen for a change in rpm.

    You can try larger diameter rear tires, a taller gear ratio, or overdrive trans. There is a lot of info on these topics in the forums, waiting for you...
     
  4. Chryco Psycho

    Chryco Psycho Well-Known Member

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    Eddy 1406 carb correct ?
    I have spent hours trying to tune these pieces of crap , they belong in the trash & are the worst possible choice for a carb .
    Fitech will work far better even though it is a throttle body not port injection system .
    Often the booster may have an internal leak is the brake line a single line , if anything is teed into the line brakes will suffer , hydroboost is a great system if you have power steering
     
  5. temsinc

    temsinc Member

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    Thank you all for the sound advise. I will start with looking for an intake leak etc. What is a good "taller" rear gear ratio for Hwy use?

    P.s. I forgot to mention I have an MSD IGNITION AND ROTOR...the rotor was just replaced and the tech could not get the car dialed in....$600 later (oh that's Canadian pesos). He claimed to have set the timing and I do believe he looked for a vac leak as well.

    The Eddy seams to be a real POS, everything I described above is how I purchased the car btw.

    Just want the old girl to run top notch and stop when I need her too lol. Thank yall again. Ciao.

    I don't know what I did loading the pics below, just meant to upload the two, none the less, there is my 70 Barracuda...she turns allot of heads here up in Medicine Hat, Alberta, Canada. Arrivederci!

    Regards,

    Darcy
     
    Last edited: Apr 15, 2018
  6. temsinc

    temsinc Member

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  7. moparlee

    moparlee Well-Known Member

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    If you want a nice highway cruising gear, go with the 2.76 gear. You'll run lower rpm's and get better gas mileage. Nice '70 Cuda!
     
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  8. Chryco Psycho

    Chryco Psycho Well-Known Member

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    sounds like you have 3.55 gears now , 3.23 are the next step or 2.76 for mostly highway but it sure changes the off the line performance .
    Nice Cuda !
     
  9. tonysrt

    tonysrt Well-Known Member

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    I have a 1406 on a stock 318 in a 74 Duster with 2.76 gears and it runs pretty good. When I 1st put on Manifold and carb, I had problems but not carb related, timing and bad pushrods. The freaky thing was that it ran ok with the 2 bbl, so you never know what you'll run into with 40 plus year old cars.
     
  10. moparleo

    moparleo Well-Known Member

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    Get a baseline. Check initial timing with vacuum advance disconnected and carb vacuum port plugged. check idling manifold vacuum. You say it is a numbers matching car with everything on the engine changed. What has the previous owner been able to tell you about the running issues ? Open chamber heads ? Stock 318 shorblock with 340 heads, RPM intake, 4 bbl carb, "mild cam" (what does that mean)Lift, duration c/l. Std. torque convertor ? Rear end gear ratio. You really need to know exactly what you have to make educated changes and adjustments. Torque monster but falls flat on acceleration ? Get more info before you start throwing money at the "problems" Here are some calculators for tire and gearing ratios.
    Wallace Racing - Calculate Speed for given RPM, Rear Gear Ratio and Trans Gear Ratio
     
  11. Steve340

    Steve340 Well-Known Member

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    A faulty brake booster will cause a loss of engine vacuum. You could try disconnecting it and see how the engine runs. Another one that can cause problems is the vacuum modulator if the car is an automatic.
     
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  12. moparleo

    moparleo Well-Known Member

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    I think only GM had a vacuum modulator.
     
  13. DetMatt1

    DetMatt1 Well-Known Member

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    Mine had drivability issues last year and it turned out at least some of it was a leaky booster.
     
  14. Railroadrider

    Railroadrider Member

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    FWIW, I put a 2.76 in our '70 318 way back in the early 80's. The car originally had 3.23. I went from 18 mpg (only when I was attempting to get all I could out of a gallon) to 20 using those same throttle/driving inputs.
     
  15. Don Gould

    Don Gould Member

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    Quote "He claimed to have set the timing and I do believe he looked for a vac leak as well."
    That's scary... WHERE did he set it? According to the original specs? Did he find a vac leak? What is the vacuum level at idle?
    Where is the Vac line connected Passenger or Drivers side?

    Quote 'The Eddy seams to be a real POS"
    So does this surprise you? They're just a visual copy of an AFB, there we're 270+ different AFB's made all very specific to the application... So Edelbrock decided that 3 or 4 would get the job done? No consideration for changing fuel formulations or aftermarket upgrades. If Carter/AFB thought they could keep up to the industry and maintain the high quality standards of their name and still remain competitively priced do you really think they would have sold the design? Eddy doesn't make those carbs they are only the marketing agent.

    Quote: "318 w/mild cam"
    Mild? what do you consider mild? a 230 duration at 50 is mild to me and a 270+ duration at 50 would be what I consider a radical bump stick. Lets get some real numbers at 50.

    Quote:"Secondly, I find that at low RPM, I loose my brakes"
    Sounds like it's probably timing to me? So lets get some facts, where is the timing set at Idle with no vac line connected (initial).
    Where's the total timing?
    What RPM does it all come in at?
    Where does the timing go to when you connect the vac line to the Distributor?
    Is this a stock distributor or aftermarket, if after market what brand?
    What coil are you running?
    What is a "MSD IGNITION AND ROTOR" R2R? Street Fire? 6AL? Distributor? Control Box?

    Quote:"Edelbrock RPM Air Gap intake" nice intake, we never use them on any engine smaller than a 388/340 with RPM range to 7,000, never on a 318 at 5500.

    Quote:"340 Aluminum Heads" So your using a head with at least 10CC more in the combustion chamber so you dropped out .5 Compression so it was probably a 8.1:1 motor now it's maybe as low as 7.5:1. Do some math and see where your really at.

    So what I see is possibly too much cam (unknown) for the compression, too large of an intake to maintain air velocity to help scavenge the combustion chamber, too large of Valve (2.02/1.60 I assume) for the air volume so you have very low velocity over the intake valve.

    Get us real numbers and possibly we can get it tuned well enough to drive decent.

    Trust me EFI is not your solution
     
  16. cudamark

    cudamark Member

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    What do you have for an exhaust system? If it's the stock 318 manifolds, that can cause a big bog on acceleration. On the brake issue, we need to know what the actual intake vacuum reading is before doing anything. It's a good indicator on what might be your hesitation problem too. I'd run a compression test too....with a real pressure gauge, not, an electronic "guess" type.