Setup for 750DP on this 408

Fuel and Air Systems

  1. 70DusterBob

    70DusterBob Well-Known Member

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    Here's what's in the 408:

    · HP & Torque: 445 HP / 500 FT LBS
    Compression Ratio: 10.1:1
    Aluminum Heads: Eddy RPM's
    Flat Tappet Cam
    Forged Pistons

    Block:


    Cylinders honed on computer controlled machine to within .0002 straightness and roundness

    4.000" Bored .040" over

    Rotating Assembly:

    · New Cast steel crankshaft
    4.000" Stroke
    OEM type 6.123" connecting rods w/ 150,000 psi bolts
    Forged pistons
    External

    Cylinder Heads:

    · Aluminum Cylinder Heads - 63cc chamber
    2.02" intake/1.60" exhaust valves
    171cc intake/77cc exhaust runners

    Cam Specs:

    · Cam Type: Flat Tappet
    .545 Intake .545 Exhaust
    241 Intake / 247 Exhaust duration
    @ .050 - 110 degree lobe separation

    Ignition Timing:

    · 34 degrees total at 2500-3000 RPM


    I need to know how to set up the jets, the power vavles, whether or not to put 50cc acc pumps on it, which cams, anything else that would prove helpful as a starting place to run it at.
     
  2. 318willrun

    318willrun Utube channel 318willrun

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    Is it a single plane or dual plane intake?
     
  3. 70DusterBob

    70DusterBob Well-Known Member

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    Eddie air gap, dual.
     
  4. 318willrun

    318willrun Utube channel 318willrun

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    just a wild guess off the top, I'd start with 73 jets primary/82 secondary with a 10g power valve.
     
  5. 70DusterBob

    70DusterBob Well-Known Member

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    Should I need the 50 cc acc pump?
     
  6. 318willrun

    318willrun Utube channel 318willrun

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    you'll not know until it's together and running. Only your motor will know what it wants for jets, nozzle size, accelerator pump size and cam size, and power valve.
     
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    • Demonracer

      Demonracer 71 Demon 00 Ram 16 Chrysler 300S 05 Caravan FABO Gold Member

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      What he said^^^^^.
       
    • 70 Buster 340

      70 Buster 340 Carbon Footprint FABO Gold Member

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      What carb was on it for the dyno pulls, there is your baseline.

      You didn't say the intended use, street, street strip or drag only
      A 50cc pump 'can't hurt' ... you can adjust the delivery volume/time with cams/nozzles

      BTW: sounds like a real nice piece.
       
    • cudajames

      cudajames FABO Gold Member FABO Gold Member

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      I have the same engine with 16 initial and 34 total - all in by 2500 I went with an 850dp - rejetted mains to #74 My afr gauge usually around 14.6
       
    • 70DusterBob

      70DusterBob Well-Known Member

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    • 70DusterBob

      70DusterBob Well-Known Member

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      Yeah I thought of the use after I posted. Street, mainly highway. Have the afr gauge, will try to maintain 14.6. It was sitting while down for repair and the acc pumps dried up. Something is clogging a passage, need to rebuild it. Afr was bouncing between 11 and just over 14 on the highway. It was flooding fuel when decelerating. To a stall when I stopped. Got it started and home, will clean soak the carb before assembling again.

      It is a really nice engine. Has 3" pipes all the way. It got about 9mpg, hope that was due to the flooding.

      Although it is mainly a cruiser, I love to take off too.

      Thanks
       
    • 70 Buster 340

      70 Buster 340 Carbon Footprint FABO Gold Member

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      You sure don't want to wash off those precision honed walls.
       
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      • 70DusterBob

        70DusterBob Well-Known Member

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      • 70DusterBob

        70DusterBob Well-Known Member

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        I have carb cleaner, you just leave it in there so long, not too long. Used it before with no issues. I only put the metering blocks and the bowls in it. But I know that stuff is super strong. One sniff and you can tell.

        Ordered the 50cc acc pumps, I am familiar with changing the shooters, jets, and cams. Just wondering where to start. I got some good advice, will follow.
         
      • Mattax

        Mattax Just the facts, ma'am FABO Gold Member

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        @70 Buster 340 is talking about the flooding.

        A. Check the fuel level running at idle. Adjust as required. Check it again after test run.
        B. Then tune for best performance. Use doesn't matter except for drag strip focused cars - and even there only a little - mostly because runs are always somewhat cold compared to temperatures on a long highway drive.
         
        Last edited: Mar 21, 2020
      • 70 Buster 340

        70 Buster 340 Carbon Footprint FABO Gold Member

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        Right... flooding the cyls with fuel washes the oil off the cyl walls and causes excessive wear.

        The 11-14 bounce and flooding on decel sounds like it could be a bad power valve or even a mismatched/bad/shrunk metering block gasket.
         
      • Mattax

        Mattax Just the facts, ma'am FABO Gold Member

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        Tuning for Performance.
        This requires systematic trial and error to improve performance. Performance defined as power, torque and engine efficiency.

        Start at the idle and work up.
        Idle and off idle are your foundations. If its crappy at idle then the engine is going to have to clear up before it can respond to additional throttle.
        Performance here is going to be demonstrated by running fairly clean exhaust output and how little throttle is needed
        (manual) to get into first gear without stalling.
        (automatic) lose the least rpm when placed in drive. Alternatively have the best vacuum at a given rpm in drive.
        Work with initial timing, idle speed screw (transfer slots), and idle mixture screws.

        Next confirm off-idle has good performance by very slowly accelerating from stop with no hesitation. This test minimizes the role of the pump shot and focus on the idle circuit's begining of transition.
        If that's good, then test more normal acceleration (for public streets) from stop to make sure the pump shot is not too much or too little for this basic job.

        Then you can test out steady driving at various speeds. The fuel ratio at steady interstate highway speeds is determined by main jet and its air bleeds. Local highways is partial or completely idle circuit (transition slot, idle feed restriction and idle aiir blleed).
        If its too lean, it will surge. Slow down and take it back to garage. Increase primary jets.

        If you have access to the strip or dyno you can test wide open throttle in 3 or 4th. AFR is controlled by the jets plus power valve channel restrictions. Change jets for the best mph through the lights.
        If primary jetting for best power is different than jetting for best interstate highway mpg, adjust the power valve restrictions.

        All the above tests are effected by timing. If you change timing at a given rpm and condition, then retest before change fuel mixture for that condition.

        Once all that is tuned, then concentrate on transition conditions. They are:
        opening the throttle quickly from low rpm (pump shot).
        power valve opening point.

        Reality is you may have to go out of sequence. You will almost certainly have to make repeats. How many repeats depends on how much interest and persistance you have.

        Good luck!

        A little more about AFR for different conditions
        Power Valve Selection: The Definitive Answer
         
        Last edited: Mar 21, 2020
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        • mderoy340

          mderoy340 Well-Known Member

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          30cc pumps are fine. Orange cam #1 hole front and rear 33 nozzles. My brothers 408 60' is 1.48 with this setup. A stroker pulls a lot of signal thru the booster.
           
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          • 70 Buster 340

            70 Buster 340 Carbon Footprint FABO Gold Member

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            Rule of thumb ..from what I can still remember... lol
            30cc - dual plane, longer stroke, higher vacuum and booster signal/airspeed works fine
            50cc - single plane - kind of invert to above and if your convertor is too tight.
             
          • 70DusterBob

            70DusterBob Well-Known Member

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            Oh, so that's what you meant. I thought you were referring to over cleaning the carb, lol. Yeah, I didn't think of that. It ran good for 15 miles, then I hit first doing about 20mph and it super sucked the intake. I think that blew out the power vavle, or sucked something into a passage. After that it was problematic with the fuel. Started irratic, then got to flooding in about 10 miles when decelerating. I will keep that in mind if it happens again, but it shouldn't.

            Thanks
             
          • 70DusterBob

            70DusterBob Well-Known Member

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            Went ahead and ordered the 50cc pumps. do you know if I can use the 30 cc pump cams with it? the kit comes with two cams, a different lever, and the housing.
             
          • 70DusterBob

            70DusterBob Well-Known Member

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            Right, I have to keep the fuel level low because of the idle. I will have to keep an eye on that and adjust x necessary
             
          • 70DusterBob

            70DusterBob Well-Known Member

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            Will give that a try, that's a great 60'
             
          • 70DusterBob

            70DusterBob Well-Known Member

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            My guess was the power valve. It's been sitting 10 months. Had gas on it but emptied 10 months ago. Could be the meter block gasket. I'm replacing everything to be safe.
             
          • 70DusterBob

            70DusterBob Well-Known Member

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            will do
             
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