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Holley choke horn removal?

Discussion in 'The Hokey Ass Message Board' started by Mr. Sinister, Jun 27, 2011.

  1. Mr. Sinister
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    Mr. Sinister Member

    Hey guys. I've been considering removing the choke plate on my 670 Street Avenger (vacuum secondaries) to maybe get a little more flow (I never use the choke). Then it got me thinking, why not mill the entire choke horn down? I read somewhere that this can be good for 30cfm of airflow. My engine is right on the edge of where I'd need to step up the carb size from my research, so instead of ponying up the dough for the next size up, I thought maybe this would be a good way to go. I've also found my engine prefers a vacuum secondary carb over a double pumper.
    My question is: Is this a good idea, and is it even worth it on a vacuum secondary carb? I've done some research on the 'net and have seen no real drawbacks to doing this, but I haven't seen anyone do it on a vacuum secondary carb.
    Thoughts?
  2. Mr. Sinister
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    Mr. Sinister Member

    I should add that I run a slightly dropped base 4x14 K&N X-Stream (filter media lid) filter.



    [​IMG]
  3. Mr. Sinister
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    Mr. Sinister Member

    Generic pic of a Street Avenger:

    [​IMG]
  4. wingman9
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    wingman9
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  5. Bucksnort
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    Bucksnort Member

    Yep,you can do that.But not a huge fan of the avenger.Have a fondness for the double pumpers myself.Guess in Md.you can get by w/o a choke most of the time.Cheaper than buying new carb but,of course,you gotta completly disassemble to make sure all the shavings are out.
    Used to mod 4224's all the time for tunnel rams,cut the choke horns with a hacksaw and blend with a Dremel.All backyard stuff.Decided one day to buy a pair of high zoot,everyone is running them carbs from a big outfit.Those did not run any quicker than my home built ones on my M/P.
    Little more info on motor,car?
  6. Mr. Sinister
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    Mr. Sinister Member

    I've seen those things, but not much on how well they work.
    What do you think about just removing the choke plate? I keep mine wired open and it looks like a real restriction, especially as air moves across the top of the carb, basically cutting the back half of the primaries off from maximum airflow.
  7. porknbeaner
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    porknbeaner Member

    Someone told me that the choke horn or air horn has a lot to do with how your idle circuite works or the proper function of your idle circuite.

    K&N stub stacks make a lot of difference they fit under your air cleaner so no one will see it.
  8. Deuces
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    Deuces Member

    Ditto!!!!!
  9. Deuces
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    Deuces Member

    I'd leave it on there... 'Cause when you think about it, it actually helps with the low end torque till the secondaries kick in.. Just get yourself a Stub-Stack and drop it on there...
  10. Larry T
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    Larry T Member

    About the only difference you'll see with a milled air horn is when you look at the carb.
    Nuther vote for Sub Stack, if you're really trying to improve the air flow. But I don't think you'll feel any seat of the pants difference there either.
    Larry T
  11. borntoloze
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    borntoloze Member

    I've done it to a 600cfm vac Holley years ago. Didn't/don't have access to a milling machine so I used a hacksaw ... cut two slits in the air horn with a hacksaw then snap off between the slits with pliers (continue doing this until the entire horn is removed). Once most of the horn has been removed, finish it off with a die grinder and a burr, then blend it smooth with a die grinder and a cartridge roll. Carb worked fine without the horn ... truth be told, I have no idea if it added 30cfm but it would have had to have helped flow into the carb. I felt that complete removal of the air horn would help air flow more than just the addition of a "stub stack".

    Now that you've all stopped laughing :D, I do know it sounds crude but once the horn has been removed and the entire area blended, you would not know that the removal wasn't done by a pro machinist/race shop.

    I do not know how much it helped flow (not having access to a dyno or a flow bench) but I can tell you, that carb worked just fine after the removal ... no idle issues or anything of that nature.
  12. Deuces
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    Deuces Member

    I've also milled the horns off a 600 and a very rare List-4223 850 "Center Squirter"... I could kick myself in the ass for hacking that one up.. :eek::eek:
  13. lippy
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    lippy Member

    I don't know about milling the airhorn on a street deal. Holley claimed if you leave the airhorn leave the choke butterfly in it actually enhances flow.
  14. Deuces
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    Deuces Member

    Yep! That helps with running a "BIG" carb on the street....
  15. propwash
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    always amazes me when some folks think they can improve on the performance of a product with thousands of hours of R&D - if any Holley would flow better without an airhorn, the company would most assuredly produce that version.
  16. Larry T
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    Larry T Member

    They do sell carbs without airhorns.
  17. 1971BB427
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    1971BB427 Member

    They sell carbs without choke plates too. Both of the 450 Holleys I bought for my tunnel ram came without choke plates from Holley.
  18. fiveohnick2932
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    fiveohnick2932 Member

    Ive heard that the K&N stub stack increases yout CFM and works quite well. I have one but have not been able to put it on because my air cleaner gets in the way a little bit so I just left it on the shelf. I hope to use it soon on another project though!
  19. Mr. Sinister
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    Mr. Sinister Member

    55 Chevy 210, not terribly heavy from my experiences pushing it up my driveway and into my garage by myself. :)
    ~11:1 350 (Vortec block, crank and rods, Keith Black hyper 10.8:1 pistons, Fel-Pro head gaskets, running older style heads & intake) cleaned up Edelbrock Performer RPM heads with Scorpion 1.5 rockers RPM intake, Comp XR294HR cam, Hooker Super Comp headers, 2.5" duals, dumped flowmasters. Ignition consists of a MSD 6AL box, Blaster 2 coil and Billet RTR distributor, with a Delco low vacuum advance can (running ported vacuum, not full manifold, that's a different issue) and 1 silver/1 blue spring on the mechanical advance.
    Trans is a TH350 with a shift kit and a 2500 stall, but I can't seem to get more than 1900 rpm out of it. Rear is stock 55 housing, 57 center section, Eaton posi, 3.55 gear. Never been to the strip, but it's walked more than a couple high 12 second cars on the street (not condoning street racing, we have our safe spot).
    When I picked the carb out, the only difference between Holley recommending the 670 or the 770 was my shift RPM. I was shifting it at 5500, but with a couple tweaks, I now shift at 6000, and I could probably shift a little higher, but I'd like the production bottom end to last. This is why I was thinking a little added CFM couldn't hurt, if this would indeed add CFM. The cars runs pretty well as is. Plugs are a light brown, but have a little wetness around the base, probably due to the cam. It does slobber a bit down low. It doesn't make a tremendous amount of power below 3500, and will barely spin the tires if I punch it from a dead stop. That's not all bad, I suppose. It will fry them up if I power-brake it, and keep them spinning through most of first. The second gear WOT shift produces a nice spin.
  20. squirrel
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    squirrel Member

    If it runs better with a vacuum carb compared to a double pumper of the same size, that tells me that your carb is too big already....

    but then I'm not much of a hot rodder, I use chokes on my old cars.
  21. Mr. Sinister
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    Mr. Sinister Member

    Well, my Holley is a 670vacuum secondary, the Demon was a 750 Race Demon double pumper. 2 very different carbs. If a 670 is too big for this engine, I'm selling it and buying a Honda, lol.
  22. squirrel
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    squirrel Member

    Oh....that make sense! If you don't use the choke, then go ahead and cut up the carb and see how it works.

    But first, how much have you played with the secondary spring?
  23. Larry T
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    Larry T Member

    Let's see, your engine is probably somewhere between 80-90% volumetric efficieny. Holley says that a 350 at 6000 rpms at 100% VE needs about 625 cfm. So that would would put you in at a little under 600 cfm.

    Beep, beep.
    Larry T

    BTW, we ran a 750 double pumper on a circle track engine that turned about 7500 rpms.
    Last edited: Jun 27, 2011
  24. Mr. Sinister
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    Mr. Sinister Member

    I run the light spring in the secondary. This produces the best "seat of the pants" feel.
  25. Mr. Sinister
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    Mr. Sinister Member


    See, I plug in my specs with a maximum rpm of 6000 on that link and I get 750-770. My setup matches the "Highly Modified" definition perfectly. This is what I did originally, but used 5500 rpm instead. That's how I ended up with the 670. That's the rub, I'm right on the edge of needing to step up, and the 500rpm where I shift is making the difference. I'd rather stay on the smaller side to keep low end power up.
  26. Larry T
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    Larry T Member

    Here's another link:
    http://www.4secondsflat.com/Carb_CFM_Calculator.html
  27. Mr. Sinister
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    Mr. Sinister Member

    This is the issue I'm having, lol. One guy says this, another says that. Even the calculators don't give me the same results.
    I had an old Holley 600 that I ran before the 670, and the car was a DOG with that carb.
  28. Mr. Sinister
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    Mr. Sinister Member

    I emailed Barry Grant with all my specs to get their opinion. I'll post their reply when I get it.
  29. borntoloze
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    borntoloze Member


    Sorry, I don't agree with this comment at all. The airhorn was clearly not designed by Holley to enhance flow, it was designed to allow the carb to be equipped with a choke. If the car owner is willing to run without a choke, then removal of the air horn can only enhance air flow. Just because a company designs, produces and markets a product, that does not mean that the item can't be "tweaked" for better performance. Isn't that what hot rodding is (or used to be) all about. And yes (as someone else mentioned) Holley actually does sell "chokeless, blended/radiused/smoothed" carbs. Ever seen a choke or choke tower on an NHRA Pro Stocker?


    "Emailed Barry Grant" ... I might be wrong but I thought I read not too long ago that they closed down/are out of business.
  30. lippy
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    lippy Member

    I guess I don't understand. I have had a wide variety of holley's on a wide variety of different chevy's. I have had out of the box 600 vac sec carbs on 454's, I have had the old 780 vac sec on 454's 780 vac sec on 283's. you name it. I never really had a problem with one of them being so out of whack I couldn't make it run correctly. Whether by pump nozzles, pump cam, powervalves, jets, sec springs ect... I think instead of spending a ton of money on different carbs I'd hire a well known tuner with a chassis dyno to do it and just have it over with. Unless you like changing carbs all the time. Got a good shop or tuner guy around there? JMO..Lippy

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