View Full Version : easiest way to remove the choke horn on a holley


muscl car
12-06-2007, 09:58:02 PM
i'm thinking of removing the choke horns and both my holley 660's and is there an easy way to do this . i've heard of using a hacksaw and file and also the drill press/lathe method like what we've got in our race shop . besides removing the obvious like the main body what else needs to be removed in order to prevent damage to the main body while removing the choke horn

Vintage Musclecar
12-06-2007, 10:09:29 PM
Honestly, cutting off the airhorns on a Holley isn't worth the trouble unless you have a hood clearance problem and are forced to run a short filter.

muscl car
12-06-2007, 10:13:30 PM
Honestly, cutting off the airhorns on a Holley isn't worth the trouble unless you have a hood clearance problem and are forced to run a short filter.

i'm running very small 6" dia air cleaners with 1-3/4 inch tall base plate and with 4' tall filters the choke horn looks to me like it's obstructing airflow into ea carb

Vintage Musclecar
12-06-2007, 10:22:31 PM
FWIW, I've seen more carbs with air horns lopped off than I can count. I'm still waiting to see a car pick up any significant performance from the modification.

However, if you're dead-set on doing it, the best way is to completely disassemble the carbs and have a machine shop remove the air horns with an end mill. Make sure they leave the float bowl vent boss intact. While they're at it, might as well get it out of the way and have them mill the metering block surfaces flat as well as the throttle body mounting surface. I don't care if the carbs are brand-spanking new outta-the-box units, none of those surfaces are flat from the factory.

Eric

Dirt Reynolds
12-07-2007, 04:32:28 AM
I ran a 3310 Holley (750 vacuum secondary) on my old 413/Vortec combo. The car went from 13.49 @ 101.8 with the stock carb to an eventual best of 12.15 @ 110.5 with the airhorn milled off and jetting changes to the secondary side. That along with a set of 275/60 BFG drag radials made the biggest improvements at the track. Milling off the airhorn made a big difference in my case.

69CHVL
12-07-2007, 07:26:09 AM
The choke horn is bigger than the venturis, so the choke horn shouldnt be an issue. UNLESS - the aircleaner is right up against the choke horn. I picked up 2mph just taking off my aircleaner at the track. I have a 1.75" drop base air cleaner that's the problem, its less than an 1" from the horn.

onovakind67
12-07-2007, 07:29:25 AM
We picked up about 8 rwhp essentially putting the air horn back on a Holley 2-bbl with a carb hat.

Vintage Musclecar
12-07-2007, 08:47:43 AM
Considering the small air cleaners on there, you might...might see a performance gain by cutting off the towers, but I'd personally experiment with some sort of larger air cleaners before I started cutting up the carbs.

http://i114.photobucket.com/albums/n261/musclcar/Picture.jpg

As far as the HP main body conversion, I've never done it using a 660 to start with, and since the 660 uses a funky accellerator pump design (hence the name "center squirter"), I'm not sure how that would play out. Unless you added a secondary metering block at the same time, you wouldn't be able to use the rear accellerator pump system on the HP main body. Plus, the 660 baseplate isn't designed to be used with an accellerator pump linkage on the secondary side, so you'd have to swap baseplates to a standard 750 DP-style at the same time. You would also have to add a secondary float bowl that has provisions for an accellerator pump since the 660 only uses a single 50 c.c. pump on the primary side. Lastly, with the additional (required) metering block on the secondary side, you may wind up having to turn the carbs sideways on the intake to make everything fit again, which them means you'd have to re-design your throttle linkage, etc. etc. etc.

Nice little snowball effect there just from one potential modification (HP main body), no? LOL!. ;)

Anyhow...my advice would be to try some larger air cleaners first to see if the car runs better with them, then go from there. It's alot easier than pulling the carbs down and carving them up.

*EDIT* last time*

(I used the wrong formula to calculate square inches of filtering area.)

hhott71
12-07-2007, 09:28:34 AM
drill press/lathe method
That would be an interesting machining operation,
I hope that a mill (think Bridgeport) was used instead.

Either way. The hacksaw, die grinder, cut-off wheel, file etc method is just as effective and very cheap, only costing you time.

Dirt Reynolds
12-07-2007, 09:34:05 PM
All my runs at the track both before I milled off the choke horn and after were done without an aircleaner. It wouldn't fit with the stock, flat steel hood on my '77 with the Victor Jr.

74RAT
12-07-2007, 10:22:43 PM
i use the die grinder with a cut off wheel method,, and then file it. this one i blended it down in a bit farther and radius'd the upper rim corners/blended the center section into the venturies. just some aluminum and carbide burrs and some sanding rolls. if all you've got is time,, what the heck. this is a holley 850 d/p. hope it helps.
andy
click image for bigger picture:
http://img1.putfile.com/thumb/4/9721592615.jpg (http://www.putfile.com/pic.php?img=5177225)
http://img1.putfile.com/thumb/2/5021513390.jpg (http://www.putfile.com/pic.php?img=4820759)

Damon
12-08-2007, 08:25:00 AM
I agree that it's helpful when you have limited clearance to the air cleaner lid. Any less than a bare minimum 1 inch from the choke horn to the air cleaner lid and it's going to be restrictive (not to mention the air won't flow into the venturis in a smooth, orderly way- it'll be turbulent and can have bad effects on fuel metering).

Lots of people don't consider how much "free height" there is between their carb and air cleaner lid. They figure if it's fits, it's fine. But my experience is that getting a good amount of free height over the carb is one of the single best things you can do to get the most from your combo. It's just one of those things I've banged my head against enough times that I check for it automatically now- like checking to make sure the gas pedal gets the throttle all the way open.

Like I said, a full inch is the absolute bare minimum. The more the better.

Bikefixr
12-08-2007, 08:37:38 AM
Not worth the effort. Several years ago one of the car mags did a test and found no measurable gain on the 400 SBC dyno motor. They needed to seriously obstruct the entry to measure any gain at all. What DID add HP and TQ was 2 things. They used a Holley stub-stack and that alone added 9HP and 11lbft at 6000 RPM. Quality of air entry seems more important. They also found that tall, round stacks added some HP and TQ. A long column oof air will flow faster and enter the body easier that a short column will. The same article also showed that a Holley main body, not properly milled and contoured, LOST some HP because the metering got thrown off as air raced across trhe top of the air bleeds and not directly into the orifice. Seems the choke horn prevents turbulence and keeps the air in a column. The pre-milled bodies by Proform are all over the place used for $50 or so. I'd be more concerened with the air column being able to turn the corner out of the carb base properly without smashing into the manifold bottom. Manifold designs from years ago never envisioned the HP, RPM and displacement of modern engines. The air velocity is so high that the column can't make the turn. If your manifold bottom is clean under the carbs, your mixture is hitting the floor and washing it clean. I think contoured spacers and properly ported maanifolds are the secret to finding hidden HP. My 402 stock-appearing rebuild will have a fully ported intake, heads and exh manifolds done with the extrude-hone process. Great idea, but pricy. But it makes sense.

Dirt Reynolds
12-08-2007, 09:57:28 PM
Not worth the effort. Several years ago one of the car mags did a test and found no measurable gain on the 400 SBC dyno motor.

I hate to argue about this but I'm going to have to disagree with that. I don't know the specifics of that 400 Car Craft tested, but I run 400 motors in my Z and in my personal one man's experience I picked up a TON of power with a milled airhorn. There is no way no how anyone is going to convince me that it does not help a high performance engine make more power. I gained almost 9 mph in the 1/4 from just milling the choke horn on a 3310 and jetting up the secondaries a few sizes. It made a HUGE difference on my previous 413ci small block to the point it was shocking, and I have the progression of timeslips sitting right here to prove it.

Air moves around differently under the hood flying down the 1/4 mile track than it does when an engine sits in a room stationary on a dyno. I don't know if that means the airflow is any worse or better, but it does move differently. Because of the incredible increase in power I experienced in my own personal case from milling off the choke horn, I did it also to the new 830 Holley I put on when I went to a new 408 combo. And -- if milling off the choke horn did absolutely nothing to very little for power, then none of the carb builder companies out there including Holley, would be selling carbs with choke horns either removed, or castings without a choke horn like the HP or Dominator series. On page 68 of How to Build Horsepower, Vol. 2, Dave Vizard mentions milling off the airhorn increases airflow through the carb on a flowbench by up to 45 cfm.

Proof is in the pudding -- if milling off the airhorn did nothing for performance then I might have picked up 1-2 mph, maybe a tad more, from jetting alone. My engine obviously needed more airflow than what a stock 750 3310 Holley provided and once the airhorn was removed my mph at the track went through the roof.

ZS10
12-08-2007, 10:56:35 PM
My suggestion is to just buy proper mainbodies.
I've seen the claim of more cfm several times with removed air horn, thats what prompted me to change it up. I had NO issues with horn to lid clearance either.

A couple years ago I bought a Proform mainbody for my 3310, and it was the best bang for the buck I've had on my car. I was really impressed with the difference. I don't know how much was due to the lack of air horn specifically but, I certainly wouldn't spend hours hacking on a carb when you can just go buy one that works.

Dirt Reynolds
12-09-2007, 01:36:37 AM
My suggestion is to just buy proper mainbodies.
I've seen the claim of more cfm several times with removed air horn, thats what prompted me to change it up. I had NO issues with horn to lid clearance either.

A couple years ago I bought a Proform mainbody for my 3310, and it was the best bang for the buck I've had on my car. I was really impressed with the difference. I don't know how much was due to the lack of air horn specifically but, I certainly wouldn't spend hours hacking on a carb when you can just go buy one that works.

I didn't spend hours hacking on a carb. Took maybe 20 minutes with a hack saw and file. Didn't cost me a thing except a little time and effort. And I'd say gaining almost 9 mph in the 1/4 for my efforts wasn't too shabby. If you want to spend the money on a ready made part then do it, but I don't see a problem with a guy willing to modify existing parts and getting more out of them.

rebski
12-09-2007, 03:22:39 AM
Wth the price and availability of H.P. style main bodies not to mention screw in air bleeds I no longer use up my shop time modifying old style main bodies.
In the old days the correct way to do it was with a mill and a flow bench to check your work. I would see a gain of 40-45 cfm on the 4777 holley. I would step up and buy the holley main body if possible. Not to say that there is anything wrong with the proform ones just my choice.
Then again If you must make shavings and get your exersize by all means have at it. LOL

Dirt Reynolds
12-09-2007, 03:52:29 AM
Then again If you must make shavings and get your exersize by all means have at it. LOL

The original poster didn't ask about Proform or Holley HP main bodies -- he asked what was involved in home-modifying his *existing* Holley 660 carbs to remove the choke horns.

And let's see -- 101.8 mph to 110.52 in the 1/4 and cost was zero. Yep, I'll take it.

rebski
12-09-2007, 05:31:42 AM
OK Dirt you want to be critical.

I gave an example of the correct way to do it just read the above post!!
Now here is the backyard way to do. Take the carbs down to the body then tape off the air bleeds , boosters and the ends where the blocks or plates bolt up you want to protect the passages from shavings. Chuck it up in your vise make a jig to hopefully keep you damn hacksaw on track then make a ruff cut leaving an eighth of an inch from where you want to be for hand finishing. Now if your real lucky you might have access to a real bansaw the nice upright pro type make a small shim to set the body on then double check it with a square and go for it. Since you have changed the flow across the air bleeds you are going to have to screw around with them to get the thing back to where it will idle correctly better get out your lettered drill index and your gas anailizer cause with dual quads on the street you are going to be into that. For the setup he's got I wouldn't mess with the horns I would go to a different filter setup.

muscl car
12-09-2007, 02:16:20 PM
The original poster didn't ask about Proform or Holley HP main bodies -- he asked what was involved in home-modifying his *existing* Holley 660 carbs to remove the choke horns.

And let's see -- 101.8 mph to 110.52 in the 1/4 and cost was zero. Yep, I'll take it.


yep all i want to do is remove the choke horns on my holley 660's and not concerened about hp carbs or proform main bodies .those will not work on a 660 carb anyways and with my 6" dia air cleaners using a 4" K&N filter i've got only 1 inch above the choke horn

Dirt Reynolds
12-09-2007, 07:22:48 PM
yep all i want to do is remove the choke horns on my holley 660's and not concerened about hp carbs or proform main bodies .those will not work on a 660 carb anyways and with my 6" dia air cleaners using a 4" K&N filter i've got only 1 inch above the choke horn

Right. And you can do it at home with a hacksaw and a file. I just went out into the shed and had at it. Then I hit it with some brake cleaner afterwards and a rag, and I was done. Did the same thing to my 830 annular Holley also. No issues at all with the idle afterwards with either carb. Another friend of mine did the exact same thing to the 830 Holley in his '72 Camaro RS with a solid-roller 383 -- that car at one point ran in the high 10's n/a and it's street driven. This isn't rocket science. Some guys seem to like to make a mountain out of a molehill -- if you already have the carb it's a zero-buck mod. I can substantiate my results with timeslips and that's all that matters to me in the end.

74RAT
12-10-2007, 06:57:41 PM
yep all i want to do is remove the choke horns on my holley 660's and not concerened about hp carbs or proform main bodies .those will not work on a 660 carb anyways and with my 6" dia air cleaners using a 4" K&N filter i've got only 1 inch above the choke horn

yep,, and if the engine actually wants more cfm,, then it'll respond positively better. or if the airhorns are restricting flow as they are,, then it'll improve. like dirt said,, his engine probably needed the extra airflow and showed a very positive increase. if you're already overcarbed and / or without a restriction,, then you probably won't see hardly any change at all.

my combo asks for about 950-1000 cfm,, so with my little 850 d/p,, i'm hoping this air horn blend will cover some of the gap till i can afford a dominator carb and intake setup. with my thinned throttle shafts and smoothed up boosters and venturi's,, i'm hoping i can knock on 930cfm or so for now. not flowbenched of course. or at least over 900cfm. all i had was time. my labor was free and i had the carb already. i say go for it. take it apart to do the work,, and clean it up well afterwards.
andy