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Thread: Is Dual 750's too much?

  1. #1
    396_WAYS_TO_SPIT
    I looked around and I have 2 holley vac sec 750's identical. Is this too much carb. I pulled off my heads and I just found out I have a .60 455 olds. I will be going bigger on the cam. I have the tunnel ram. I have some carbs. I really dont want to buy new carbs because I have these 2 already and they are in very good condition(1 brand new).
    thanks for the help guys,396

  2. #2
    Hotcrusader76
    396_WAYS_TO_SPIT:
    I looked around and I have 2 holley vac sec 750's identical. Is this too much carb. I pulled off my heads and I just found out I have a .60 455 olds. I will be going bigger on the cam. I have the tunnel ram. I have some carbs. I really dont want to buy new carbs because I have these 2 already and they are in very good condition(1 brand new).
    thanks for the help guys,396Those two carbs are just fine. They will need the idle circuit to be leaned out some but otherwise you should see great results.
    Also consider having the vacuum canisters simeased (SP?) together. This way the secondaries open up at the same rate off engine vacuum. You can do this by tapping the tops of these two canisters with some hose or braided line. Easy modification!
    Otherwise invest into some 660 Holley's. They rock!
    Call me if you need anything...
    ~Ty
    [ November 15, 2002, 07:29 PM: Message edited by: Hotcrusader76 ]

  3. #3
    396_WAYS_TO_SPIT
    Thanks ty, I will be getting hold of you when the motor goes back in.
    396

  4. #4
    Blown 472
    Why would you want to run a carb designed for idle or wot, that is all the 660 is good for.

  5. #5
    gnarley
    Hotcrusader76:
    Those two carbs are just fine. They will need the idle circuit to be leaned out some but otherwise you should see great results.
    ~TyTy Don't you think that 1500 CFM on a naturally asperated 455 Olds + .060 about 470 CID that can probably only turn about 5000 RPM is a bit on the fat side??? I sure do & think it will be on the lazy side & just suck the fuel! Don't you think that a better choice would be around 1000 CFM or even less? The throttle responce will still be a bit lazy even then.
    How To Calculate CFM:
    Engine size (CID) x maximum RPM / 3456 = CFM
    CFM @ 100% volumetric efficiency = 679.97

  6. #6
    HM
    Some people may have forgot that Holley Vac Secondary Carbs are quite dialable.
    396, since you already have the carbs, no need in wasting money when you have carbs that can be totally dialed in for your olds. I am sure Ty can give you more specific pointers, but you can change the springs on the secondaries so that they come in late, early, or not at all - making the dual 750's act more like dual 375's.
    I am running dual 750's DP's on my 350 Chevy. Granted I have a blower making 12 lbs boost and a GIGANTIC roller cam, but, the dual 750's run really nice in general. I also had the benefit of dialing the carbs in on a Dyno.

  7. #7
    cyclone
    I ran dual 750HP's on my naturally aspirated 455 Olds and it ran perfectly. Those carbs will be fine.

  8. #8
    hack job
    gnarley:
    Hotcrusader76:
    Those two carbs are just fine. They will need the idle circuit to be leaned out some but otherwise you should see great results.
    ~TyTy Don't you think that 1500 CFM on a naturally asperated 455 Olds + .060 about 470 CID that can probably only turn about 5000 RPM is a bit on the fat side??? I sure do & think it will be on the lazy side & just suck the fuel! Don't you think that a better choice would be around 1000 CFM or even less? The throttle responce will still be a bit lazy even then.
    How To Calculate CFM:
    Engine size (CID) x maximum RPM / 3456 = CFM
    CFM @ 100% volumetric efficiency = 679.97i run two 750 dp s on my noramly asperated ford they seem to work fine!
    in fact most builders will tell you to run the 4779 or the hp version of the same carb. they are one of the best carb out there! wink

  9. #9
    gnarley
    [QUOTE]Originally posted by hack job:

    i run two 750 dp s on my noramly asperated ford they seem to work fine!
    in fact most builders will tell you to run the 4779 or the hp version of the same carb. they are one of the best carb out there! wink

    It's probably a 460 ??? They have huge intake runners & need CFM to make them work so I am told, but how do Olds 455's react to that much CFM? do the heads work well with that much? Sure you can do it but what works the best?

  10. #10
    Hotcrusader76
    The point here is....he wants to use his existing carburetors so that no more costs are encured with his investment. Now because I am a simple person, I could work those 750 VS enough to where to he will run great.
    I also supply my vacuum secondary customers with extra springs so they may dial in the best time to open the secondaries.
    For a Jetboat application....660's are the best. For someone running a simple Big block, there would be no complaints with one of TPC Racing's 660 Carburetors.
    Funny thing is I could even get him set-up with Dominators for that Olds, but why pay the cost to de-tune those suckers to work.
    To be continued...

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