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Technical Chevy 6 cyl dual carb set up ?'S

Discussion in 'The Hokey Ass Message Board' started by bkrpop, Nov 14, 2014.

  1. bkrpop
    Joined: May 14, 2009
    Posts: 37

    bkrpop
    Member

    I'm swapping out an original 216 from my 52 chevy to an original 235 out of a 62 impala. I;m considering running a dual carb set up on the 235 and I have NEVER run dual carb on anything before so I would appreciate any help I can get.
    I see dual carbs selling as "primary" and "secondary". Should I run something like this or, what I was thinking, I could run the smaller 1bbl Rochester from the original 216 as a "primary" carb and the slightly large 1BBl off of the original 235 as a "secondary" carb.
    If this setup is do-able, would a progressive style linkage or a simultaneous linkage be better? I would think in my un-knowledgable opinion that progressive would be best. Also, would both carbs need to be choked? Again I would think only the "primary" would need a choke.
    Thanks for any advise, info, tips and pix.
     
  2. need louvers ?
    Joined: Nov 20, 2008
    Posts: 12,912

    need louvers ?
    Member

    On a dual carb set up, I wouldn't try to run them progressive. There would be no reason to. That means you no longer have to be concerned with primary and secondary carbs.

    Grab two matching 216 or 235 carbs, mount them, synch them, tighten up the linkage and be done with it... Also be ready for many times more seat of the pants power, as most straight sixes are woefully under carbed to begin with.

    About "synching" - That is the act of getting the carbs to open at EXACTLY the same time. An easy way to get there before bolting them to the manifold is to close the curb idle screw until the screw just touches the linkage. Ten, take a .010 feeler gauge and insert it between the butterfly and the carb body, adjusting the idle screw to just touch the linkage again. Do that with both carbs, then bolt them on. You'll be close enough to get it up and rolling with just that. A 30.00 Synch tool off of E-Bay will also be a good purchase, too.
     
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  3. As will a hose to your ear
     
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  4. jcmarz
    Joined: Jan 10, 2010
    Posts: 4,636

    jcmarz
    Member
    from Chino, Ca

    216 Carbs will only work on a 216 intake. 235 Carbs for 235 intake. And because of the way the Carb linkage is set up, can't use progressive linkages.
     
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  5. HUSSEY
    Joined: Feb 16, 2010
    Posts: 628

    HUSSEY
    Member

    I don't know what kind of backlash I'm going to get from this but how about three carbs with two dummy carb? You get the look without all the headache.
     
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  6. Inked Monkey
    Joined: Apr 19, 2011
    Posts: 1,539

    Inked Monkey
    Member

    I love my carbs from Tom Langdon. Bolt on and go!
     
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  7. need louvers ?
    Joined: Nov 20, 2008
    Posts: 12,912

    need louvers ?
    Member

    I'm not entirely sure why multiple carbs are considered a "headache"... About the only thing "weird" about running them is synching them. Once you understand it, the accounts for about 5 minutes of the car's life. After that, keep stuff clean, make sure your fuel pressure is regulated and you'll have no further problems than you would with one carb.

    On a straight six, I'd never consider running ANYTHING BUT multiple carbs.... Unless it's s turbo!
     
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  8. joel
    Joined: Oct 10, 2009
    Posts: 1,486

    joel
    ALLIANCE MEMBER

    2 carbs and split ex. manifold; can't beat it.
     
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  9. Road Runner
    Joined: Feb 7, 2007
    Posts: 1,242

    Road Runner
    Member

    Before you go with 2x1 carbs, you should first install dual headers for exhaust, like Fentons.
    Extra carbs don't add much power, when the engine can't breath with single exhaust.

    I got two 1bbl Carter W1 574s on my daily 235 (see link) and it's the simplest, most reliable carb combination I found.
    The trick is to go with 2 smaller 216 carbs for a street 235.
    Larger carbs are too much and run too rich, unless you have a bigger cam and do other high-rpm mods to the engine.
    To fit a 216 2x1 intake to the 235 you can either enlarge the intake ports to 235 size, done by a machine shop, or you can also go with 216/235 adapter rings. Both options cost about the same.

    You can find good cheap Carter W1 574S model cores all over the place and there are places online that sell quality carbs kits.

    The commonly available Unisyn tool is alright, but inaccurate.
    Get a small motorcycle carb balancer with dial and adjust at part throttle with equal numbers for both carbs.
    The smallest adjustment makes a big difference.
    And perfect balance between the two carbs is really noticeable.
     
  10. gir431
    Joined: Mar 25, 2007
    Posts: 70

    gir431
    Member

    I've been running two Holly-Webber carbs on an Edmunds water heated manifold with Fenton headers for 25 trouble free years. Regardless of what configuration you run, you must heat the carbs otherwise you will have cold running issues.
     
  11. IMG_20141115_142445.JPG I'm looking at running three on my Holden six, which is an Australian smaller copy of the Chev.
    I'm worried it'll be over carbed, so thought about running the centre one only.
    Would rather run all three, and thought I may get away with it by running smaller jets.
    I'm using Aussy Strombergs.
     
    Last edited: Nov 14, 2014
  12. Road Runner
    Joined: Feb 7, 2007
    Posts: 1,242

    Road Runner
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    3 carbs are in theory ideal for a straight 6 with 3 intake ports.
    3 carbs generally help the engine breath better at high RPM, but don't perform too well for a street driven engine, unless each carb is rather small or a 2bbl carb.
    And for a street engine we need a heated intake, especially during the colder months.

    Jet sizes, within small margins, help adjusting for ideal fuel/air mix ratio, altitude and ethanol/gas mix, but a too small jet in a too large carb or the other way around messes with the venturi effect required to get ideal F/A ratio.
    More than one carb slows intake air speed for each carb and jet size alone doesn't compensate.
     
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  13. need louvers ?
    Joined: Nov 20, 2008
    Posts: 12,912

    need louvers ?
    Member

    Ya know, there is a blanket statement that has already been repeated a few times in this thread that I need to dispel. You NEED a heated intake... Ever see what a heated intake does to fuel on a 120 degree Phoenix day? I'm not trying to make you guys that are repeating this feel bad, but our climates in this country vary quite wildly, and in some of them you just flat don't want manifold heat! Just think about where you are before you let someone tell you that you have to have anything.
     
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  14. jcmarz
    Joined: Jan 10, 2010
    Posts: 4,636

    jcmarz
    Member
    from Chino, Ca

    Right on. The factory manifold uses a butterfly that closes when it reaches a certain temp so it's not intended to constantly heat the intake. It's only to help in cold weather starts. Chevy V8s had a exhaust valve on the passenger side for the same purpose. How many of us threw them out when we installed headers?.
     
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  15. bkrpop
    Joined: May 14, 2009
    Posts: 37

    bkrpop
    Member

    I probably should have notes that I already have Fenton dual/split exhaust. My (again un-knowledgible) thought on dual carbs was based on the basic 4bbl, small in front and big in back. 2 of the same makes sense too though. I also wondered about fuel pressure, would I need an adjustable regulator? Or two regulators? I don't want to get into a debate about heated intakes, I'm concerned w dual carbs. I personally ran the 216 w/out the manifold heated and never had problems and doing donuts in the snow. Lol any major differences between Fenton dual intakes and Offy other than Offy's look cooler and cost more? Thanks for all the advise and tips guys!!
     
  16. need louvers ?
    Joined: Nov 20, 2008
    Posts: 12,912

    need louvers ?
    Member

    One regulator set at about 3-5 psi will be just fine for both carbs.

    The deal with the heated manifold is that so many of the manifolds had water passages at both ends to take the heater hoses. People insist you need them, so in the summer here I spend quite a bit of time helping people with vapor lock problems and poor fuel mileage, hard starting and other issues caused by heating things. I don't mind the business, but when folks start arguing that isn't the problem 'cause so and so said it's how it needs to be, it just gets old.
     
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  17. belair
    Joined: Jul 10, 2006
    Posts: 8,018

    belair
    Member

    Contact Tom Langdon. He is a Chevy 6 cylinder guru. He can answer all you questions, and has all parts you need. He is honest, knowledgable, and will get you squared away. I doubt there is a lot of difference in the Offy and Fentons. Pick the one you like best or that Tom recommends. I have a Thickstun, and it will take some doing to make it work. If you live in colder climates, you may need to heat the manifold to keep the carbs from freezing up. I have never needed the heat.
     
  18. bkrpop
    Joined: May 14, 2009
    Posts: 37

    bkrpop
    Member

    Is tom Langdon on the hamb?
     
  19. Dave Downs
    Joined: Oct 25, 2005
    Posts: 843

    Dave Downs
    Member
    from S.E. Penna

    On the subject of heat to an in-line manifold, it is not about hot or cold weather or about 'better starting in cold weather'. It is about humidity more than temperature (actually a combination of both) causing ice to form in and on the carb. The inline engine is more prone to this problem because the manifold hangs on the side of the engine and does not get the heat that a 'V' engine does to the manifold. Piston aircraft engines used in light aircraft (most are 'flat' 4's or 6's) have up-draft carbs mounted under the engine with little engine heat available.

    Live in Arizona where it is dry - no heat needed, live on the coast of Washington with high humidity it is necessary.

    Read this for more info: http://en.wikipedia.org/wiki/Carburetor_heat
     
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  20. Road Runner
    Joined: Feb 7, 2007
    Posts: 1,242

    Road Runner
    Member

  21. So if you live somewhere that is colder but quite dry is there a need for the heat?
     
  22. He is not, but I am, and I work here at Stovebolt with Tom. So, you can hit us up through me, or by calling us, or going to our website. Any way is fine. Were on Facebook too :)
     
  23. These are two often confused issue. Carb Icing is what you are referring to, and why jet planes have carb heaters. Otherwise the venturis would eventually close up .
    Intake heat, although similar in nature will not matter whether it is humid or not, or any ambient temperature. Read the tech article, and understand that in some extreme cases, you need BOTH carb heat AND intake heat. Typically, everyone driving a carbureted vehicle needs a form of intake heat. From the factory, this was addressed with the exhaust, where the exhaust mated to the intake and was modulated with a heat stove. As people transition to headers, this functionality is lost, and needs to be replaced. A great easy way to accomplish this is water heat. You get a flow, from an inlet and outlet, so the temperature maintains consistency, and you won't have the manifold refrigeration issue.
     
  24. Gman0046
    Joined: Jul 24, 2005
    Posts: 5,482

    Gman0046
    Member

    If it were me , I leave the stock 235 alone and save the money. An extra carb will make NO appreciable difference in performance.
     

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