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BRINGING IT ALL TOGETHER.... A's, G's & E's


3 posters

    carburetor confusion

    softesttouch
    softesttouch


    Number of posts : 64
    Location : montrose,colorado
    Registration date : 2010-10-22

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    Post by softesttouch Thu Oct 16, 2014 2:03 pm

    my 1966 gmc has a 6 cylinder 230ci and has a carter yf carb, but since ultimately i am looking for max cfm for that carb, i am trying to discern exactly which carter yf it is........i have a gmc maintenance manual printed in 1964 that states the carter carb for the 6-banger is the 3821S, BUT in 1964 the engine was only a 194ci, whereas by the year of my van (1966), the engine was a 230ci. did that carb likely change with the engine change, or is it probably the same 3821S? is there a way to look at my carb and tell exactly which one it is?
    kookykrispy
    kookykrispy


    Number of posts : 1533
    Location : Helendale, CA
    Age : 50
    Registration date : 2009-05-22

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    Post by kookykrispy Thu Oct 16, 2014 2:22 pm

    I came across a source that stated that the Carter YF is 215CFM. I remember I had a carter YF on my old '66 sport van. Two club members has a YF, both factory equipment: on a 66 sport van, and also on a 67 G10. Most likely the same carb as you have.
    softesttouch
    softesttouch


    Number of posts : 64
    Location : montrose,colorado
    Registration date : 2010-10-22

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    Post by softesttouch Thu Oct 16, 2014 3:13 pm

    okay, so based upon all the great info you've posted, the calculator tells me that for the 250 stroker i'm building, max cfm (at 4400rpm--I keep coming across that number in old gmc/chev van spec charts) needed is about 270...............well beyond the 215 you found the carter to be capable of. that sounds like a significant impediment. choices are going back to your suggested dual carb, or......is there another simple 1 barrel that would fit what I've got and give me the cfm's im needing? I am excited about the 250 stroker (looking into the 307 pistons) but it will all be for naught if the whole system is bottlenecked by carb intake diameter.
    Twinpilot001
    Twinpilot001


    Number of posts : 6186
    Location : spokane ,Wa.
    Registration date : 2009-09-28

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    Post by Twinpilot001 Thu Oct 16, 2014 3:16 pm

    Twinpilot001
    Twinpilot001


    Number of posts : 6186
    Location : spokane ,Wa.
    Registration date : 2009-09-28

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    Post by Twinpilot001 Thu Oct 16, 2014 3:17 pm

    softesttouch
    softesttouch


    Number of posts : 64
    Location : montrose,colorado
    Registration date : 2010-10-22

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    Post by softesttouch Thu Oct 16, 2014 3:35 pm

    looks serious.....i don't think air flow will be the limiting factor with these!
    kookykrispy
    kookykrispy


    Number of posts : 1533
    Location : Helendale, CA
    Age : 50
    Registration date : 2009-05-22

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    Post by kookykrispy Thu Oct 16, 2014 4:33 pm

    softesttouch wrote:okay, so based upon all the great info you've posted, the calculator tells me that for the 250 stroker i'm building, max cfm (at 4400rpm--I keep coming across that number in old gmc/chev van spec charts) needed is about 270...............well beyond the 215 you found the carter to be capable of.  that sounds like a significant impediment.  choices are going back to your suggested dual carb, or......is there another simple 1 barrel that would fit what I've got and give me the cfm's im needing?  I am excited about the 250 stroker (looking into the 307 pistons) but it will all be for naught if the whole system is bottlenecked by carb intake diameter.

    Yes. Take a look at this thread:

    http://www.inliners.org/ubbthreads/ubbthreads.php?ubb=showflat&Number=48397&PHPSESSID=75a737a96b0d6edf523ea88b148dc22f

    You will note that Rochestor B series carbs or Rochestor Monojet carbs have different size throttle opening and venturi sizes. Both of these factors increase CFM flow capability.

    If you can find one of the large throttle & venturi size Rochestor BC carbs that is referenced here, that would be able to flow enough:

    Next - the carb I find on early 292's, I think it was also used on the "HiPerf" 230/155hp in 64.
    196cfm
    273cfm
    1-9/16 vent
    1-3/4 throt
    Jet #70 to #72

    Another idea is to run an 2bbl to 1bbl adapter, so you can use a rochestor 2bc or other 2 barrel carb of your choosing.

    http://www.streetsideauto.com/p/transdapt-2025/

    carburetor confusion 2025
    softesttouch
    softesttouch


    Number of posts : 64
    Location : montrose,colorado
    Registration date : 2010-10-22

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    Post by softesttouch Fri Oct 17, 2014 8:33 pm

    i found several Rochester B on ebay. I just need to make sure i end up with the one I need AND make sure it's no taller than the level of the engine housing. looking good!
    kookykrispy
    kookykrispy


    Number of posts : 1533
    Location : Helendale, CA
    Age : 50
    Registration date : 2009-05-22

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    Post by kookykrispy Fri Oct 17, 2014 9:53 pm

    The rochestor B was one of the factory carbs. It is the same height as the monojet or carter YF.

    I have 4 of 'em, but they are all 1.5" throttle size
    kookykrispy
    kookykrispy


    Number of posts : 1533
    Location : Helendale, CA
    Age : 50
    Registration date : 2009-05-22

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    Post by kookykrispy Fri Oct 17, 2014 10:05 pm

    Since you are looking specifically for the rochester with the big throttle bore and large venturi, You might also call these guys, and simply tell them exactly what you are looking for:

    http://www.thecarburetorshop.com/Carbsaleapplication.htm

    I note that they have a #7027009, which according to this ebay listing, is correct for 1967 292 truck, so this might be the big 1bbl carb you are wanting

    http://www.ebay.com/itm/63-64-65-66-67-CHEVROLET-GMC-TRUCK-292-NOS-ROCHESTER-1BBL-CARBURETOR-7027009-/371115582137?pt=Vintage_Car_Truck_Parts_Accessories&hash=item56683662b9&vxp=mtr

    The ebay carb is NOS and costs a staggering $499.  Ouch.  

    For that price, you could have a 2x1 or 3x1 multicarb setup with a Offy intake.
    kookykrispy
    kookykrispy


    Number of posts : 1533
    Location : Helendale, CA
    Age : 50
    Registration date : 2009-05-22

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    Post by kookykrispy Fri Oct 17, 2014 10:25 pm

    One more note:  usually the 4 barrel intake and carb does not fit well in the early van doghouse.

    If you are considering a multicarb setup, you can also consider a offenhauser 3x1 intake

    http://www.speedwaymotors.com/Offenhauser-5414-1963-75-Chevy-6-Cylinder-Triple-Carb-Intake-Manifold,7003.html

    Run the center carb as the primary, and then the outers as the secondaries on progressive linkage.  Spendy, but pretty cool, and I'll bet it would be a good performer.

    I have one of these in my stash that I intend to use one day on a 292 project.  However, that will require that I modify the doghouse lid to fit the front carb. I think if you ran a 230-250 engine, it would all fit under there. The 292 is about 1.5" taller than the other engines.

    carburetor confusion 5605414_L
    softesttouch
    softesttouch


    Number of posts : 64
    Location : montrose,colorado
    Registration date : 2010-10-22

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    Post by softesttouch Fri Oct 17, 2014 11:04 pm

    it's all scarcity vs. abundance, supply and demand, how bad I want it, etc.....but what would you expect to pay for a rochester like i'm looking for?
    kookykrispy
    kookykrispy


    Number of posts : 1533
    Location : Helendale, CA
    Age : 50
    Registration date : 2009-05-22

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    Post by kookykrispy Sat Oct 18, 2014 12:07 am

    Yeah, whats funny, is I used to just chuck 1bbl carbs in the trash because they were so plentiful! I used to have so many of them, lol. I'm honestly not sure what other places charge for a core carb, hopefully not too much, but I guess they are becoming rare? Ugh. I would just call the number in that carb shop link above and see if they have a 1-9/16" venturi, 1-3/4" throttle Rochester B carb, and how much they want for it. Hopefully the price will be reasonable, heck its still just an old 1bbl carb! You can rebuild these single barrels yourself, its really easy and the kit is only about $30.

    You also might consider the Monojet. I actually prefer the Mono. Its a great carb with good drivability. Get one of the earlier non-smog versions, or simply plug & seal all the additional smog fittings etc. if you have to use a smog era one.

    To muddy up the waters even more, here is an article describing how the CFM's of 1bbl carbs are usually not measured the same as a 4bbl.

    http://www.candsspecialties.com/ratings.html

    Another thing to consider is how often are you ever going to actually rev the engine out to 4400 rpm? Going to a 250 crank will bump the torque up at all the RPM's, and so will running flat top 307 pistons. You'll get better performance all through the power band, not only the top end. With that in mind, ask yourself do you really need this carb? Is an additional 10% more airflow really going to matter that much? If you really want the extra airflow, maybe consider a multicarb setup. Then you know for sure you'll have plenty of air to your engine.
    softesttouch
    softesttouch


    Number of posts : 64
    Location : montrose,colorado
    Registration date : 2010-10-22

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    Post by softesttouch Sat Oct 18, 2014 7:59 am

    you've made a very good point. this isn't intended to be my every-day, weaving-in-and-out-of-traffic, haulin'-ass-to-work vehicle. this is gonna be my sunday-driving baby. you keep mentioning the monojet, and I will check it out. also, maybe the thing to do is just rebuild my original carter yf for $35, and see what happens. if the performance is adequate, it's a done deal. if not, you have given me numerous options to consider, and I have really learned a lot through this thread. many thanks for your great input.

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