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Old 06-27-2011, 07:42 AM   #1
Mr. Sinister
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Default Holley choke horn removal?

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?
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Old 06-27-2011, 07:50 AM   #2
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Default Re: Holley choke horn removal?

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



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Old 06-27-2011, 07:51 AM   #3
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Default Re: Holley choke horn removal?

Generic pic of a Street Avenger:

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Old 06-27-2011, 07:54 AM   #4
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Default Re: Holley choke horn removal?

If you can do it yourself it's probably worth it, but it seems like a lot of work for minimum gain. You might try a K&N insert to smooth out the entry flow first.
http://www.knfilters.com/Racing/stubstacks.htm
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Old 06-27-2011, 07:59 AM   #5
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Default Re: Holley choke horn removal?

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?
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Old 06-27-2011, 08:00 AM   #6
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Default Re: Holley choke horn removal?

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.
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Old 06-27-2011, 08:03 AM   #7
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Default Re: Holley choke horn removal?

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.
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Old 06-27-2011, 08:08 AM   #8
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Default Re: Holley choke horn removal?

Quote:
Originally Posted by wingman9 View Post
If you can do it yourself it's probably worth it, but it seems like a lot of work for minimum gain. You might try a K&N insert to smooth out the entry flow first.
http://www.knfilters.com/Racing/stubstacks.htm
Ditto!!!!!
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Old 06-27-2011, 08:15 AM   #9
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Default Re: Holley choke horn removal?

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Originally Posted by Mr. Sinister View Post
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.
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...
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Old 06-27-2011, 08:22 AM   #10
Larry T
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Default Re: Holley choke horn removal?

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.
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Old 06-27-2011, 08:27 AM   #11
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Default Re: Holley choke horn removal?

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 , 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.
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Old 06-27-2011, 08:34 AM   #12
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Default Re: Holley choke horn removal?

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..
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Old 06-27-2011, 08:34 AM   #13
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Default Re: Holley choke horn removal?

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.
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Old 06-27-2011, 08:39 AM   #14
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Default Re: Holley choke horn removal?

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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.
Yep! That helps with running a "BIG" carb on the street....
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Old 06-27-2011, 08:46 AM   #15
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Default Re: Holley choke horn removal?

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.
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Old 06-27-2011, 08:48 AM   #16
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Default Re: Holley choke horn removal?

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Originally Posted by propwash View Post
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.
They do sell carbs without airhorns.
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Old 06-27-2011, 08:57 AM   #17
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Default Re: Holley choke horn removal?

They sell carbs without choke plates too. Both of the 450 Holleys I bought for my tunnel ram came without choke plates from Holley.
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Old 06-27-2011, 09:02 AM   #18
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Default Re: Holley choke horn removal?

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!
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Old 06-27-2011, 09:28 AM   #19
Mr. Sinister
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Default Re: Holley choke horn removal?

Quote:
Originally Posted by Bucksnort View Post
Little more info on motor,car?
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.
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Old 06-27-2011, 09:48 AM   #20
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Default Re: Holley choke horn removal?

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.
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