4 Barrel Carb or not?

Discussion in 'The Garage' started by skidxr, Oct 24, 2013.

  1. skidxr

    skidxr Excuses

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    I have an old (1978) Minnie Winnie class C motorhome on a Dodge 1 ton van chassis with a 360 motor. It currently has a 2 barrel carb on it and I'm wondering if it would be worth it to install a 4 barrel carb and manifold. I'm looking for more pulling power. It already sucks down the gas so mileage really isn't a concern.

    Thank you...
    #1
  2. uraberg

    uraberg whosaberg?

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    The question is, do you want pulling power at low rpms or at higher rpms. In a simplistic view, this is the difference between a 2 and a 4 barrel carb.

    You might be able to better tune your carb, or look into a 4 barrel progressive.
    #2
  3. ttpete

    ttpete Rectum Non Bustibus

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    What you have is a 35 year old vehicle that is probably overloaded when packed to travel. Weigh it ready to go on a trip and compare that with the GVW plate on the door jamb. It eats gas because you've got your foot in the carburetor most of the time. I'll bet you get around 6 or 7 MPG, and that's not unusual for pushing a square box that probably weighs 5 tons or more down the road.

    I don't see where a 4 barrel carb will be worthwhile. Holley makes a 500 cfm 2 barrel carb, and you might keep that in mind. But you'll need someone to set it up and jet it properly. That 360 is just too small for the application. It should have had a big block 440 in it with enough torque to cruise easily.
    #3
  4. gravityisnotmyfriend

    gravityisnotmyfriend Long timer

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    I"ve got a 1978 Ford Econoline Camper. It's got a 351 with a 2 barrel. My mechanic told me that I'd actually get better gas mileage if I put a 4 barrel on it. He says that the 2bl restricts too much airflow. If I had a 4 bl I wouldn't be sticking my foot all the way in the carb so much.

    The guy is pushing 80 and has been turning wrenches all his life. He's never been wrong when it's come to any car problems I've taken to him, so I take his advice pretty seriously.

    I rarely ever drive that rig, so I'm not too terribly bothered by the 2 bl carb, but that's one seasoned mechanic's advice.
    #4
  5. JonnyCash

    JonnyCash turd polisher

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    I think you'd do better with a progressive 4bbl carb, as your mechanic says. In most of your driving, you'd be running on 2 small venturis, which works better for a light load, and then for acceleration or hill climbing, you'd have the big secondaries in reserve. Would it be worth the cost, I have no idea, because I don't know what it would cost.
    #5
  6. skidxr

    skidxr Excuses

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    Thanks all.. I figured I would do it if it was a no brainer. I was just thinking about turd polishing when I noticed your status Johny.. To funny.
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  7. kubiak

    kubiak Long timer

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    if i remember correctly get a 4 barrel spreadbore carb. smaller primaries and big secondary bores. it will run on the primary bores cruising around getting better mpg then if you need more power floor it and the big secondary bores open up. i would look for a small cfm 4 barrel like a 450 to 600 though.
    #7
  8. concours

    concours WFO for 41 years

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    Changing to a four barrel would be a lateral move. That 2 bbl flows all the air/fuel that engine needs at the speeds it's being used at.

    Many, many myths stated above. Spend the money on beer/fuel.
    #8
  9. Motornoggin

    Motornoggin Two-Bit Throttle Bum

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    A 4bbl conversion would help. Might not notice a huge difference, but if the 2bbl is old and out of tune, it might make a pretty big difference.

    A cam change to a modern dual pattern cam would help even more, but that entails a LOT of work, especially in a van cab...

    I say go for it, you can buy an intake and carb for between $500-$600. If you're equipped to do the work yourself, it won't cost a lot more than that. Also, make sure everything else is up to snuff, ignition, plugs, wires, etc... Not going to do you any good if it's not tuned up. A '78 will have a low compression engine too, might bump the initial timing by 2-4 degrees and maybe even play with the curve. Would improve response and maybe even help fuel economy.

    Exhaust; what kind of shape is it in? Coated headers would help. Doesn't have to be loud with good mufflers.
    #9
  10. RVDan

    RVDan Long timer

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    Often switching to a 4 bbl will provide more even fuel distribution resulting in better fuel economy and mid range power
    #10
  11. ragtoplvr

    ragtoplvr Long timer

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    if it does not have it you need a dual exhaust with at least 2 inch pipe or a super single with 2.5 inch diameter pipe, good big tube muffler. Glass packs are too loud for that hard working a motor. Big muffler, silence without backpressure.

    I like the AFB carb, easy to jet, good fuel atomization. 360 jetting and correct aluminum manifold and air cleaner are easy to find. You should be able to find a stock type closed filter housing with snorkel that will make things a lot quieter.

    As stated changing to a good cam will help a lot too. Pretty big PIA in most motor homes.

    And you will never ever save enough gas to begin to pay for this.

    Rod
    #11
  12. troidus

    troidus Long timer

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    Put a 5.9 Cummins in it. More work, but more satisfying when you're done.

    If you do the 4bbl, use a spreadbore. The smaller primaries will help off-idle response and part-throttle fuel economy as long as you can keep the secondaries closed. Make sure it's a vacuum secondary carb, not a mechanical one.

    I wouldn't put dual exhaust on it. You want exhaust velocity to keep your low rpm torque up. If you still have a cat, you may want to make sure it's not clogged.
    #12
  13. broncobowsher

    broncobowsher Long timer

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    So true! But as originally stated, doesn't care.

    Getting the right mix and good atomization are needed for best power, best economy, and actually do a pretty good job at running clean emissions as well. The 2-barrel can be good. A 4-barrel generally can be better. The trick is actually getting it tuned right. I know a lot of people who can tune so it runs good, but when checked with a good wide band exhaust sensor they are always off. Tune with a wide band and it gets better. More safe power on less gas.

    You may want to try that with the stock 2-barrel carb first. Many heavy duty applications were set to stupid rich for "engine cooling" under heavy loads. That is if the stock 2-barrel isn't wore out already. Sloppy throttle shafts, melted boosters, delt with lots of this crap. Time for new carb, might as well make it a 4-barrel.

    Good RV cam and sufficient exhaust are also good upgrades.
    #13
  14. RidingAgin

    RidingAgin Been here awhile

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    I second this advise, although not 80 yet.... :clap

    Having a clean new rebuild will make a difference IMO. Good luck to you.
    #14
  15. red83gt

    red83gt Adventurer

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    If u want all the benefit from a 4bbl carb on your motorhome you will need to swap out the camshaft..The 360 came in both 2 and 4bbl versions.The 4bbl has a different cam to allow for more flow in and out of the heads..My suggestion would be to get an edelbrock performer intake,cam and carb.These pieces work real good together and provide good low rpm torque between 1,100 to about 4,000 rpm,,about where your real world driving range in a motorhome is..Your mileage might increase a smidge,but you will pull hills much easier and accelerate better in traffic and such..and 600 cfm carb is as big as you need to go.I wouldn't rule out a holley carb with this set up either,its a little cheaper..I prefer the holley,,(easier to work on)the edelbrock carb looks like the old Rochester quadrajet but its better than a quadrajet.Now lets talk headers,,LOL,actually a duel exhaust with 2 inch pipe from your stock maifolds will be sufficient,exit out the sides in front of your rear wheels,,sound will bad ass!!just my .02.
    #15
  16. concours

    concours WFO for 41 years

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    This thread reads like an old J.C.Whitney catalog... "more power" "faster passing" "lower ET" "higher top end" "stronger mid range" "better MPG" "cooler running" "deep, mellow sound" :1drink
    #16
  17. Baroquenride

    Baroquenride Relaxing at the beach

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    +1
    #17
  18. concours

    concours WFO for 41 years

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    One more time, the 2bl carb is NOT the restriction limiting horsepower (at these "working engine", NOT racing speeds). A cam (the right one) would most definitely help, but combustion chamber design is also a limiting factor. The dual exhaust thing is also waaaay overblown, (again at working truck revs) Someone mentioned timing advance curve... VERY relevant to power output AND economy, but with a FULLY LOADED motorhome, the conditions for engine destroying detonation would be very close at hand. It would have to be very carefully monitored. Knock sensors on modern engines have helped us forget about this once serious danger. A lightly loaded passenger car gives more leeway.

    Summary, you could spend $2000 and 20 hours in mods, and have 3 more HP.
    #18
  19. Wasser

    Wasser Spilt my beer

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    +1

    Its the heads and low compression pistons in that 360 that are the road block. The heads have small valves and very restrictive ports.

    You could put the biggest bumpstick, a 1150 CFM double pumper and dual 3" exhaust on that tired LA series 360 and maybe notice a tiny improvement.



    The OP would be better off saving up some coin and getting a 360 crate motor from Mopar Performance.
    #19
  20. Baroquenride

    Baroquenride Relaxing at the beach

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    You're absolutely right. In my previous post I was thinking he was asking for better fuel economy and depending on driving habits and type of carb etc, could be obtained with a 4bbl. However, in re-reading the original question, that wasn't what he was looking for.
    #20