Vacuum secondary or double pumper?

Fuel and Air Systems

  1. MWFan

    MWFan Well-Known Member

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    Planning to upgrade from an Eddy 600. What would you do, 64 Polara, 440, 9.4/1 comp ratio, Magnum exhaust manifolds, Mopar aluminum dual plane, 484/284 Purple cam, 452 heads, 354 Dana, 727 pushbutton, shift kit. 750 DP or vacuum secondaries?
     
    Last edited: Jul 12, 2019
  2. 66383

    66383 FBBO Gold Member FBBO Gold Member

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    Street driving.....I'd say vacuum secondaries. Racing, DP IMO
     
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    • steve340

      steve340 Well-Known Member

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      Vacuum secondary for street/strip in my opinion.
       
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      • MWFan

        MWFan Well-Known Member

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        It may go to test n tune once or twice...but its definitely a street cruiser. I have a habit of being too conservative. I have been thinking vacuum secondary, just wanted input from people with more experience than me. That would be almost everyone here...

        Thx, Bernie
         
      • 33 IMP

        33 IMP Well-Known Member

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        3.91 up gear, dp. 3.23 down, vs. 3.54 gear could go either way, i would decide based on camshaft and converter. Under 3000 converter, vs.
        Edit: for your combo i might try an 830 vacuum. More air available without opening the secondarys, then if they do open, it will be controlled by demand, wont over- carb.
         
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        • Cojohnso1

          Cojohnso1 Well-Known Member

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          Sounds like a 750 with vac to me. I try ed my 850 DP on my 440 with simular build. Replacing 750 just to see? No noticeable increase in performance. But was more temperamental driving around. Especially if not fully warmed. And a small drop in gas milage. My GTX is a 4 speed. I can only guess an auto would be even more temperamental?
           
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          • Johnpat

            Johnpat Well-Known Member

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            I'm running Street Avenger vacuum secondarys750cfm on my
            other car 427 vet.
            Love it after tuning a Little
            Street driven mainly
             
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            • Cranky

              Cranky Moderator Staff Member FBBO Gold Member

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              TQ all the way!! Once you overcome tuning one, you'll love it! Best fuel mileage plus performance.....
               
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              • RJRENTON

                RJRENTON FBBO Gold Member FBBO Gold Member

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                Gentlemen,
                IMHO...Vacuum secondaries....the engine decides when to add the extra air/fuel and how much. Double pump carbs have their place....but just not here. You have a heavy car and needs to be allowed to get the engine in its best torque point b4 adding more fuel. Vacuum secondaries sense air flow and reacts accordingly. Just my opinion of course.
                Bob Renton
                 
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                • moparedtn

                  moparedtn FBBO Gold Member FBBO Gold Member

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                  Agreed. 750 vac sec. Maybe 800 in the TQ/Edelbrock type.
                   
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                  • BSB67

                    BSB67 FBBO Gold Member FBBO Gold Member

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                    My choice would be a DP without question. I've done a lot of carbs on both 383s and 440s. A 4779 on a slightly warmed up 383 or on a near stock 440 is better than any other carb I've tried on a dual plane intake.

                    I'd also pick an 800 AVS before a Holley vacuum carb.
                     
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                    • RJRENTON

                      RJRENTON FBBO Gold Member FBBO Gold Member

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                      Your comment "...better than any other carb I've tried on a dual plane intake".....how did you determine what was better and by how much? Did you do dyno testing or elapsed time trials? Or what or how did you make the determination? Hopefully, not by the "seat of the pants" measurement. Just curious......
                      FYI...The ORIGINAL Carter AVS, not the Edlebrock clone, is a secondary "on demand" carb that has an adjustable secondary air valve which reacts to air flow requirments, just like a vacuum secondary Holley. Mopar used a 750 CFM 4160 series Holley # R4668 on a 1971 383 HP application with either suto or 4 speed trans and A/C , it has vacuum operated secondaries. What about the six barrel / six pack application....absolutely vacuum operation: 355 CFM center carb and 500 CFM end carbs. Even the 2 x 4bbl Hemi used on demand carbs using counterweight secondary velocity air valves to control the secondary air flow....again similar to on drmand vacuum operation. Even the 400 HP and 435 HP 427 Corvette engines used vacuum operated carbs......so who is correct? I'll vote for the engine designers.....just my opinion of course.
                      Bob Renton
                       
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                      • BSB67

                        BSB67 FBBO Gold Member FBBO Gold Member

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                        Track data.

                        We also replaced the 780 on a factory L78 with a 4781, it picked up a couple tenths and mph too. Not a great example as those cars had so much more potential than the typical Mopar, but you brought it up. As if its hard to pick up the performance of a factory set up. Not an opinion.
                         
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                        • RJRENTON

                          RJRENTON FBBO Gold Member FBBO Gold Member

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                          The original Holley 780 CFM R3310 model 4150 was and still is a great carb. Out of curiosity, I'd like to see what your base line testing data was and the incremental changes made and their coverall effect. I'm always looking to improve my efforts as I have extensive carb tuning experience and would be helpful to add to my data base.....rather having to reinvent the wheel, do to speak.
                          Bob Renton
                           
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                          • moparedtn

                            moparedtn FBBO Gold Member FBBO Gold Member

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                            Yep, the 3310 almost seems like it was made for the 440 street engine right out of the box.
                            I had some old time Mopar guys tell me that in the early 80's and I took their advice on a 440 car I had then.
                            It's been the "right" carb on several 440's I've had ever since - probably going to wind up on the current one,
                            too.
                            Your radical/modified 440 may vary, of course. :)
                             
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                            • MWFan

                              MWFan Well-Known Member

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                              Thanks all for your input. Since this is a street cruiser and not a race car, I likely will go with the VS carb. Hoping for a noticeable power increase from the Eddy 600 with good driveability, not necessarily the fastest 1/4 mile time.
                               
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                              • 383man

                                383man Well-Known Member

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                                Both can work fine. Myself I like the DP carbs on all my builds. But I have run vac sec carbs with good results also. If your good with carbs then I like the DP as they are easy to fine tune if its needed. But if you don't like to work on your carbs the vac carb may be more forgiving for you. Many like the vac sec on heavy auto street cars and they work fine but I have had good results with DP on them also. Good luck to you on which ever you go with as either should work fine for you. Ron
                                 
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                                • 66Satellite47

                                  66Satellite47 FBBO Gold Member FBBO Gold Member

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                                  Your moderate motor/heavy car combo would probably be much happier with the vacuum carb. My low CR 2 BBL cam 383 liked the 3310-1 Holley many years ago. A little tuning and away you go. A more radical motor may like the DP. The DP's can be made to work great even for street aps, just takes more tuning effort. Fuel economy depends mostly on your right foot.
                                   
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                                  • BSB67

                                    BSB67 FBBO Gold Member FBBO Gold Member

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                                    Kudos to you. That is exactly what I would ask. Despite not being from Missouri, I'm a show me guy too.

                                    Data, maybe some somewhere. But at some point you need to choose what you want to believe based on the source. I'm fascinated by how there can be a ground swell of miss information that cannot be unravelled.

                                    Generally I don't talk about the road I've traveled in my hot rodding history to get where I'm at today. I'll just hit a few highlights.

                                    Almost all my experience is on street cars. Probably over 1000 track passes with my own stuff, and that pales in comparison to all the street racing I did. Along with that, there was a core group of us, usually 4 or 5 other guys that were doing the the same thing, kinda of a competition to out do each other on a week to week basis. I would change camshafts on Saturday mornings. We tried and traded carburetors all the time. All the: is a Holley better or a Carter, is big better than small, is vacuum better than DP was tested and concluded 40 years ago. But even so, today I've still got about 12 carburetors sitting around here, including a 3310-1 as you know is actually a 780 with the down leg secondary booster and rear metering body.

                                    The stuff I post always comes from real personal experience, or observation paired with experience.

                                    At the risk of sounding arrogant, when I go to the track, most folks that come by are very surprised what my cars run considering what they are.

                                    Take it for what it's worth.
                                     
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                                    • PurpleBeeper

                                      PurpleBeeper FBBO Gold Member FBBO Gold Member

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                                      3310 series Holley 750 vacuum secondary.....my 2-cents
                                       
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