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Any thought's on polishing the upper and or lower area of a carbs venturi's?

Discussion in 'The Hokey Ass Message Board' started by Littleman, Apr 1, 2009.

  1. Littleman
    Joined: Aug 25, 2004
    Posts: 2,614

    Littleman
    Alliance Member
    from OHIO, USA

    I know like head port work...their's the camp that claims polished finish and the other camp claim a not so refined surface is better......for I believe fuel atomization ect..........But what about the upper and lower venturi area of a carb ?.......Like an old 94....I was thinking of polishing the upper tapered area that leads to the venturi bore and soda blast the lower portion that tapers back out to the butterfly base..............Or you could polish the whole inside........but would that lead to the fuel possibly beading ?.........Thanks, Littleman Dave...........I know it's a little much...but what the hell...It could be worth 1/2 a tenth...hahaha?....anyone have any experience w/ this?
     
    Last edited: Apr 1, 2009
  2. Littleman
    Joined: Aug 25, 2004
    Posts: 2,614

    Littleman
    Alliance Member
    from OHIO, USA

    Anyone have any thought's ?..........Thanks, Littleman
     
  3. zman
    Joined: Apr 2, 2001
    Posts: 16,558

    zman
    Member
    from Garner, NC

    On my roadrace bikes we used to polish the air only side, once it passed the slide we left it as finished. Can't say it helped or didn't, but it sure was pretty.
     
  4. fab32
    Joined: May 14, 2002
    Posts: 13,988

    fab32
    Member Emeritus

    The only way to judge any alteration to the airflow of a carb is to put it on a flow bench, before and after alteration. Same goes for drilling jets. Your only kidding yourself if you think you can consistantly drill a jet and get repeatable results. When I worked for GM one of the quality control jobs I had was checking the flow of the jets we made for the 2CG carbs. A scratch in the bore of a jet could change the flow as much as 5-10 cc's of fuel/test time. Same with altering the venturi. Just hand sanding the parting line where the bottom and top of the die met would put the airflow off the chart.
    Just another application like cylinder head modification. They do that work in conjunction with a flow bench. If the changes upstream of the heads are not consistant why bother with precision flowed heads.

    Frank
     
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  5. Littleman
    Joined: Aug 25, 2004
    Posts: 2,614

    Littleman
    Alliance Member
    from OHIO, USA

    My flow bench is the DragStrip and the ET ticket at the other end along with a whole bunch of enthusiasm........I jet to what the plugs show me they need.......I almost put my new engine on the dyno this time, but it cost a few more bucks than I had.........and it really does not compare to doing the real thing at the track, well at my level anyway's...I do drill my jets track side, but do them another way when at home and not racing a clock at the track..My carbs are not all jetted the same as well....I have tested different ways to drill the jets and have assembled a measured set of drills and reamers and gauge pins I use..I have also seen some of the crap they sell new, like a pair of jets in the same pack that pin different from one another and w/ burrs on top of it....You can measure anything along with flow.......I find most people get caught up too much in theory or what he or she did and most of the time never end up doing anything in the end.......I do it and if it works it work.....if not I look at it as an exercise......such as altering my venturi's...it's machining that I can control and maintain the same measurements and results........But I am wondering if anyone dabbled with polished internals of carbs....and what they may have stumbled upon......I could go down the much easier road and go injection....but what's the fun in that ?.........To me doing this kind of stuff is the nuts and bolts of HotRodding....before I started I pinned and measured each carb.....not two of them matched, some where close but off in other areas, now they are closer than not by doing nothing.....This is the good stuff, nothing like being so enthused about doing something and machining into the wee hours only to wake up a few hours later to go to work.....If I had a flow bench...I would never get any sleep !.......Last summer I had some ideas to alter my squirters-size and angle of the squirt.........the ET slip improved w/ good plug reads.................I will start polishing the carbs upper area tomorrow night......Thanks for the info, Littleman
     
  6. shock
    Joined: May 25, 2006
    Posts: 223

    shock
    Member

    .....If I had a flow bench...I would never get any sleep


    If you used a flow bench thoughts on polishing venturis would be of what worth to you ?.......shit it might prove it a waste of time.
     
  7. Littleman
    Joined: Aug 25, 2004
    Posts: 2,614

    Littleman
    Alliance Member
    from OHIO, USA

    I just enlarged the venturi's.so cleaning them up is the next step !.......increased area= more air flow= give it more fuel..........= potential what?.............= speed/hp.....Littleman
     
  8. saltracer219
    Joined: Sep 23, 2006
    Posts: 639

    saltracer219
    Member

    The shape of the venturi is very critical. If you can make a gauge so you can size them all the same that will help. The relationship of the booster to the venturi is also very critical. I have had some experience with NASCAR , circle track and drag race Holleys. Without a flowbench available , just remove the flashing and polish the bores with a fine scotchbrite cross pad. Trying to do more than this, like changing the venturi shape without a flowbench, is not usually real sucessful.
     
  9. Littleman
    Joined: Aug 25, 2004
    Posts: 2,614

    Littleman
    Alliance Member
    from OHIO, USA

    Thanks for the info and taking the time to respond !...I did machine a plug to size all of them the same......we shall find out soon......The plan is to get the new combination running the # it's going to run and consistant...Then swap out the venturi altered center 94 carb bodies and see what the ET slip state's........To get different results w/ a flow bench....you first need to alter it as I did to see what the change was...it is for the most part what I am doing minus the flowbench, but the track is my flowbench......the ET slip is my data...too many people do more bench racing than anything........I spent last night working on a set of six squirters.....I knife cut the tops of them......If one would say I waste my time.....then I would say they possibly do not get it........Littleman.........is HotRodding dead?...........I will add...I am having fun doing this if nothing else !..
     
    Last edited: Apr 2, 2009
  10. Bruce Lancaster
    Joined: Oct 9, 2001
    Posts: 21,683

    Bruce Lancaster
    Member Emeritus

    There is an old magazine article by Dave Vizard that is the ONLY thing I have ever seen on internal air flow work in carbs...go buy his book on carbs and manifolds.
    He thoroughly flogged a Q-jet with flow numbers after each bit of work. There is a BIG bottomline: Anything that improves flow through the car WITHOUT enlarging the venturi is free flow that does not diminish venturi signal and cause overcarbed driveability problems. Just like the work of canny racers who improve 750 Holleys to flow like an 850 without the overcarbage...
    He did a lot of polishing and removal of mold marks and sharp corners upstairs, did the traditional slabbing of the throttle shaft below, and got very useful numbers out of the primaries...slabbing was the biggest. He then went on to bigger throttles, another big step...and note that there is a bigger throttle body available for 94's!
    He also reworked the huge secondary side...I think the Qjet went over 1,000CFM.
    Book also contains a racing flog of a stock Chevy manifold, again with some universally applicable ideas.
     
  11. Littleman
    Joined: Aug 25, 2004
    Posts: 2,614

    Littleman
    Alliance Member
    from OHIO, USA


    Thanks for the info Bruce !.........Do you happen to know what is the size of the throttle butterflies and venturi's on the larger 94's you speak of ?.....my venturi's measured .935'' Dia. and I opened them up to 1.003, and reramped the tappered area below.......I already milled the throttle shafts last year and was running them..I even made my own thinner brass butterfly's....I will look for this book....I have already done the machining so their's no turning back......I have to try what I have...if it works ..great...if not I have plenty more carb body's and am alway's looking for more.........Thanks again, Dave
     
  12. JeffreyJames
    Joined: Jun 13, 2007
    Posts: 16,588

    JeffreyJames
    Member
    from SUGAR CITY

    For a second there Dave I thought you started crossing the line into how a car looks instead of how it performs. I should have known better.

    That's not saying that your cars are not works of art and as beautiful as they are fast.
     
  13. Bruce Lancaster
    Joined: Oct 9, 2001
    Posts: 21,683

    Bruce Lancaster
    Member Emeritus

    I don't know much about later variants...and there are several families of them. I have a couple large Y-block types, will look...some of these use the big booster type inner venturis made as part of nozzle bar.
    There are Ford post-flathead ones through 1956
    there are other-make ones, International and GMC. I know that the last flathead league stock car racers in Connecticut used the internationl main bodies...
    Then pure aftermarket variants, like the bug spray.
    My collection is almost entirely 1937-48 variants, biggest is just the 1" V-12 model
     
  14. Littleman
    Joined: Aug 25, 2004
    Posts: 2,614

    Littleman
    Alliance Member
    from OHIO, USA

    Thanks again for the info everyone !...Littleman
     
  15. FEDER
    Joined: Jan 5, 2003
    Posts: 1,269

    FEDER
    Member

    How about try this. Make a base that your carb will bolt to. Put a piece of tube the same size as your intake manifold inlet on the bottom of the flange. Bolt the carb to it and hook up a shop vac to the bottom. Then take a vacume guage and run a hose from it and stick it down the top of the carb say a half an inch and see what happens.
    You can play around with hose placement for readings. Cutting the hose at a long taper may help or You could fab a metal tube to use. The more vacume You pull the more air You flow. May or may not work but wouldnt take too much time to experiment with.
    FEDER
     
  16. Jmountainjr
    Joined: Dec 29, 2006
    Posts: 858

    Jmountainjr
    ALLIANCE MEMBER

    I've seen the mid-1950's Holley 2100 with 1 1/16" venturi - however they were four bolt bases and not three bolt. The IHC model used a cast iron base and top with a normal main body - the one's Bruce referred to above. With the right collection of parts it wouldn't be that hard to build a three bolt carb into something that's bigger on the inside than the outside would lead you to believe.
     
  17. Bruce Lancaster
    Joined: Oct 9, 2001
    Posts: 21,683

    Bruce Lancaster
    Member Emeritus

    The one International I have seen up close had a body still bearing 21-29 marks, identifying it as a normal '42 Ford piece! Since it is much bigger, the reuse of those outside molds is a real touch of stealty.
    Upper and lower pieces of the IHC are so strange it is hard to recognize the familiar middle piece!
     
  18. Bruce Lancaster
    Joined: Oct 9, 2001
    Posts: 21,683

    Bruce Lancaster
    Member Emeritus

    Found an ECG...this is a circa 1955 carb.
    Mine is clearly a mongrel, but I the main body at least is ECG...throttles are about 1 3/8 inch, and would need a lot of manifold hogging! I think venturis are 1 1/16, and it has the big booster type secondary venturis on the nozzle bars. I think this makes it a 2110 type. There is an outside vac passage apparently for auto choke that will require plugging and some grinding if you want it to look like an earlier carb.
    I pretty much use 59A carbs, and I have some at least of all the earlies and '49-51 types. Anyone have a good list of late and post flathead carbs of this family?
    There are Holley listings and some manuals (including the IH) on the Old Car manual Project, but the Holley list would need some flogging and additional info for our use.
     
  19. Curly
    Joined: Jun 26, 2003
    Posts: 1,162

    Curly
    Member

    Above the butterflies.... polish till you see yourself like in a mirror. Key here would be not remove too much material and they are all the same size.

    I'd blast below the point of fuel entry.

    I used to do this with my 2 stroke bikes. I used to raise the ports (transfer ports) effectively changing intake timing (if I had a cam it would be the same as the intake valve opening sooner and increasing the duration) I polished the piss out of the exhaust, intake, intake manifold, carb venturi. I noticed it ran great wide open but at lower RPM's it would hesitate and forced my to work the throttle a little more than before the changes, not much but still noticable.

    I talked to someone about this, figuring that I had raised the port too much and he was a pro mechanic. He suggested that I texture from the point of fuel entry in the carb all the way to the point it entered the cylinder. He claimed the problem I was having was pooling/puddling of fuel due to the fact that the surface was too smooth causing "fuel droplets" to condense and no longer being atomized it would pass these droplets into the combustion chamber causing a momentary rich condition.....keeping the fuel suspended in the air is the ticket and this could be done with the proper texture.

    It also worked for me the same way when I graduated to building Harleys.

    As others have said....doing it all with a flowbench would be the cat's ass. I think you'd be shocked if you matched all carbs on a bench and the checked your flow again after they were mounted on the intake!!!!!
     
  20. 4tford
    Joined: Aug 27, 2005
    Posts: 1,596

    4tford
    Member

    I don't know about the carb but I had my intake coated inside and outside at process coatings which smoothed the intake runners for a better fuel flow. If porting helps by smoothing the runners why not smooth the whole runner with the coating which also helps with reducing heat in the intake. It's on my 392 hemi 4X2 intake.
     
  21. FAB32 - "Just hand sanding the parting line where the bottom and top of the die met would put the airflow off the chart."
    Put the airflow off the chart good, or bad? Did it improve airflow, or impede it? That's about the only place I would fool with the inside of the carb...
     
  22. Littleman
    Joined: Aug 25, 2004
    Posts: 2,614

    Littleman
    Alliance Member
    from OHIO, USA

    Really it all comes down to.....''You really do not know unless you try!''.......So that's what I am trying...Theory has never stopped me in the past, you never know what's on the other side......Thanks for all the info and help!.... Littleman
     

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