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6 carb or 8 carb log manifold?

Discussion in 'The Hokey Ass Message Board' started by oldskoolflyer13, Aug 30, 2010.

  1. oldskoolflyer13
    Joined: Mar 29, 2009
    Posts: 274

    oldskoolflyer13
    Member

    Thinkn of getting a weiand log manifold for my 331 hemi....question is...for the street is it gonna be ok? I have a choice between 6 or 8 carbs...and 3 or 4 bolt..whats the better way to go? You would think that a carb per cylinder allows better tuning...but I do know that mulit setups require tinkering. what carb would be best?

    Questions

    Good for street and performance or not?

    6 or 8 carb set up?

    which carb?
     
  2. LSGUN
    Joined: May 26, 2007
    Posts: 1,326

    LSGUN
    Member
    from TX

  3. oldskoolflyer13
    Joined: Mar 29, 2009
    Posts: 274

    oldskoolflyer13
    Member

    the thread is full of lots of issues and good info.....but kinda skips around what im looking for....like pros and cons
     
  4. strombergs97
    Joined: May 22, 2006
    Posts: 1,888

    strombergs97
    Member
    from California

    Pros, looks good..Cons, you'll have to run all the carbs, 6 strombergs is 930 CFMs thats 460 CFMs each side..Unless you have a very strong engine and lots of experience in tunning the carbs, I wouldn't run them . A 331 would need about 500 CFMs.. If is was an open plenum intake you could run progressive linkage..Think about a 3x2 or 4x2 intake..
    My thinking..
    Duane.
     

  5. LSGUN
    Joined: May 26, 2007
    Posts: 1,326

    LSGUN
    Member
    from TX

    From your post it sounds like you don't have much knowledge with multi carb setups. It's a lot harder than most think to get an engine to run correctly let alone be streetable. You should state the specs on the engine, if you think you can slap a 6x2 on a stock 331 you're waisting your time.

    If you search you can find quite a few threads packed with info. on setting up a 6x2. As Duane said, you're probably better off with something more tame by the sound of it. Perhaps a Weiand 2x4 or if you have the cash, maybe you can find something like a Cragar 4x2 intake. It's worth the headache though, nothing looks more bitchin' than a 6x2 sitting on a Chrysler Hemi, just make sure the engine earns it.
     
  6. strombergs97
    Joined: May 22, 2006
    Posts: 1,888

    strombergs97
    Member
    from California

    OK, oldskoolflyer13, here is the answer to your problem..It will perform well and look sooooooo coooooooool..I also have a 4x2 log intake..
    Three 97s will give you 450 CFMs just right for that 331..
    Duane.
     

    Attached Files:

  7. I would run the 4 bolt base because they are more plentiful. Rochestor 2Gs are good carbs.

    Its a log manifold so its just a matter of how much you want to spend for carbs etc. You can block off the carbs you don't want to use.
     
  8. Back in the day, a lot of guys ran blocked-off carbs to get the look, i.e. there maybe six deuces on the log, but only the centre pair worked.

    You could go to a pair of progressive linkages for each side, but it would still be overcarburated. Really you need to look at a fairly hot cam and headers to make a six or eight jug log work properly.

    You'll also need to learn how to balance them to make the system work properly. I've had more than four decades of experience with multicarb set-ups, everything from a pair of 97s on a blown flatmotor to four 2BBl Webers on Ferraris. Getting the carbs set up right can make the difference between making HP and having an unreliable POS.
     
  9. 73RR
    Joined: Jan 29, 2007
    Posts: 6,582

    73RR
    Member

    As said, getting all 6, or 8, to work seamlessly will be a major ordeal. Once attained, you'll love the sound as much as the look.
    Is it too much cfm? Probably not, unless the 331 is a stocker. There are plenty of 302-327-350 out there with 780 Holleys on top...but yeah, its boring.
    Give some serious consideration to your throttle linkage design. You will need to open all carbs (fuel distribution issues) slowly but you'll also want to have control under your foot (considerable pedal travel) so you can feather it if needed....alot of pedal travel but not too much butterfly action.
    Check with Scooter, he has similar plans.

    .
     
  10. oldskoolflyer13
    Joined: Mar 29, 2009
    Posts: 274

    oldskoolflyer13
    Member

    This is my first venture on multi carbs....not slapping them on a stocker. I appreciate those who have taken time to respond and really appreciate those that have put some good info in there.
    ,
    Engine plans are to punch her out, healthy cam but not over cam'd, light head mods..not sure of valve sizes, lake headers

    a lot of people say weiand dual quad and some say 6x2...im just tryn to find out what would be best performance wise...by trade im a aviation mechanic....i can learn. Just getting the game plan together...gather parts ...and get going. Pile parts for engine here...body over there...chassis over there....kinda like doing phased aircraft maintenance.

    will a dual quad perform better or a tuned 6x2?
     
  11. Littleman
    Joined: Aug 25, 2004
    Posts: 2,619

    Littleman
    Alliance Member
    from OHIO, USA

    Real soon my engine is going on a dyno...first w/ run s will be w/ a tuned four barrel and then swapped out to my six-two setup to have real data to compare...should give some real good data........The fastest my six-two's have been was 10.37 on nitrous thru all six.....they have run 10.80's on carbs w/ no power adders.....my goal is a 9.99......I ran my 327 w/ a very mild cam, like 221 dration @ .050 and 464 lift.....w/ stock 2.02 camel hump heads and w/ 10.34 compression..w/ straight linkage....it ran 12.20's after I learned to tune it and drove it to work.....It can be done if you want it....Littleman
     
  12. 73RR
    Joined: Jan 29, 2007
    Posts: 6,582

    73RR
    Member

    Go easy with the boring bar. You'll get more from the right cam and 10:1 compression than the few additional cubes. I'm not sure if you indicated which 331 you have but skip the head mods on the later big port units. You have more than enough port for 331 inches in street trim. 51-53 heads? Different story.

    "Perform" means different things to different people. In my little world I like the 'performance' of a single 4 like the 'ol 3310, very flexible, easy to tune and they make good power on a number of displacements. A good all-around carb.
    Some will demand a 2x4 for the looks and additional cfm on a big inch engine, and some want the 4x2, 6x2, 8x2 for the cool factor.
    Performance 'under your foot' is dependant on having a properly functioning assembly. One carb is one to tune/set up, dual fours is twice as many to detail, and eight carbs? It will likely be an all day chore.

    Many of us will be waiting for details on Littleman's dyno runs.

    .
     

  13. Tunning is key whether you got one carb or a dozen. If you are not willing to invest the time to tune than a single carb is the only way to go.

    Like Wildcat I've been around multi carbs or injection as long as I can remember. My first multicarb tunning experience was a pair of SUs. The old man said they were pretty hard to screw up. If you didn't grow up with more than one the learning curve can be huge. Take your time and learn to make it work you'll be as happy as a duck in mud. If you don't want to learn to tune one unless you get lucky and have a friend that knows you will never be happy with the set up.
     
  14. scootermcrad
    Joined: Sep 20, 2005
    Posts: 12,374

    scootermcrad
    ALLIANCE MEMBER

    I don't have too much to add that hasn't already been said. I think in general, Hemis like to breathe. Your plans to open it up a little more will certainly allow more CFM and I would think your plans to setup a 6x2 is probably more than OK and an 8x2 will really depend on the specs you come up with for the cam and everything else. There is some equations out there that will help you to determine what will REALLY work. If you don't already have the Complete Chrysler Hemi Engine Manual by Ron Ceridono, I suggest you get it right away. There is a whole section on the math involved for this very topic as well as a great example of setting up a multi-carb intake for your Hemi. If you have it already, then you know the section I speak of.

    Keep in mind that the design of these manifolds were for racing applications and not for street applications. There are plenty of people running them just fine, but just something to keep in the back of your mind.

    I'm setting up an Offy 6x2 with Holley 94's right now and I'm planning on starting with a straight linkage with a "non-linear" throttle arrangement that will hopefully help control the CFM's on the street. In other words, the butterflies will open gradually at the beginning and then open more drastically as more fuel is needed. Not sure if it's going to work, but I guess we'll see... I guess you could call it a "Progressive Throttle" arrangement.

    DAVE! I seriously will be looking for your data on this!! PLEASE keep us posted! I think this may clear up a ton of "speculation" on this topic. Important, in my opinion!
     
    Last edited: Sep 1, 2010
  15. Jmountainjr
    Joined: Dec 29, 2006
    Posts: 1,364

    Jmountainjr
    ALLIANCE MEMBER

    will a dual quad perform better or a tuned 6x2?

    I think there is a lot of variables that could influence that answer. In my opinion for a street car, the performance of a 6x2 is most influenced by the intake manifold. Some older styles intended for drag racing don't have very large balance tubes so do not run that good with a progressive setup. Others have too much volume, so you have isssues simular to running a tunnel ram on the street. With six carbs, you need to keep the air velocity through the carbs fast enough to get good metering. Sometimes you can improve that with 1" or 2" carb spacers. I happen to like 6x2 and I'm willing to invest the sweat equity - straight linkage vs. progressive, power valves (or not), jetting, etc.- into it to get it passable. A final note on total CFM. 2 bbl carbs were CFM rated @ 3" of vaccumn and 4 bbl carbs are rated @ 1.5". So you need to take that 930 CFM mentioned above and use about 71% of it (660 CFM) to put it into 4 bbl "speak" when you are comparing back and forth. If you don't like working on it, run the 2x4 - less work but it just won't look as cool!<!-- / message -->
     

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