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Vacuum Vs. Mechanical secondary

Discussion in 'The Garage' started by Dunc03, Jan 6, 2005.

  1. Dunc03

    Dunc03 1/2 ton status

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    I looking to get a Demon carb for my GM crate motor. The one I'm looking at is the Crate demon for the 350 HO. It comes in vacuum or mechanical secondary. What are the advantages and disadvantages to these two types of secondary. The vehicle stays on the highway for the most part. I'm just wonering what would be the better setup. The vacuum carb is about $50 more than the mechanical. Is it worth the extra money.

    The setup is 350/700r4/np208/3.42, and it sits on 33,s

    Thanks for any ideas.
     
  2. shane74

    shane74 1/2 ton status

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    I personally like the mechanical secondaries better. Once it's set, it's there all the time. No vaccum lines to crack or go bad. Then again, I'm a mechanical n-gin-ear type guy, so I'm a little biased.
     
  3. 84_Chevy_K10

    84_Chevy_K10 Banned

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    Mechanical secondaries have little or no place on a truck. Go vacuum. Especially since you're way undergeared for the tires you're running. You'll be much happier, I think.

    And get a Qjet. :grin:
     
  4. rcurrier44

    rcurrier44 1/2 ton status

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    Demons arn't a very good off road carb so don't be surprised if it gives you trouble the fiew times you go wheeling.

    But at the track they work very well.

    The only time a mechanical secondary carb is of real benifit is when you are running a setup that is so agressive that you are not getting a good/consistant vacume signal. I would go with the vacume setup.
     
  5. Dunc03

    Dunc03 1/2 ton status

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    GOT A Q-jET

    I actually have a Q-jet now, and when I hit the gas the damn thing just wants to die out. The reason I'm going with the demon is because I lack the tuning ability to make an emissions carb run on a high performance engine. Actually if I could find the right power system spring I'd keep it, but GM discontinued the one I need. So I'm going to try the demon as an alternative to going injected. Maybe injection later.
     
  6. 1-ton

    1-ton 1/2 ton status Premium Member

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    I think you should go with vacuum secondaries as well. Vacuum secondaries are better for a street driven vehicle. Mechanical is better for racing because, as stated already, mechanical secondaries are for very high performance vehicles with very little intake manifold vacuum, due to very large camshaft profiles.



     
  7. motorheadnelson

    motorheadnelson Registered Member

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    Ditto. Heavy street rigs especially with automatics like vacuum secondaries. You can get a spring kit to tailor the secondary opening. Better off road, also. Mashing the throttle with mechanical can either cause a bog or too much power. Vacuum allows what the motor can handle at the time.
     

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