Removing choke horn from carb

HSSS427 · #1 (**permalink**) 02-06-2005, 06:38 PM

I'm overhauling the Holley 750 on my 427 so. It's a 4150 model 9347, chokeless double pumper, w mechanical secondaries. Saw an article that suggest cutting the choke horn off the carb to smooth air flow. Any ideas on the pros and cons of doing this? Has anyone else done it, and what was the result?
Thanks!
Scott

DAVID GAGNARD · #2 (**permalink**) 02-06-2005, 07:36 PM

Scott;

I've done at least a half dozen carbs......First one was because I could only use a 2" air filter element and the top of the air cleaner was real close to the top of the carb.......

I have NO scientific proof,but when you look at one without the choke horn,you would think airflow would have to be improved.............there must be some merit to it,since Holley and all the major carb makers now offer carbs without a choke horn.........

If the carb is all together,I just use duct tape to tape up the venturi and everything else around,then cut off the horn about 1/4 to 1/2 inch with a hack saw and finish the job on a mill,be sure NOT to take off the center stud for your air filter rod,lucky for me,my cousin has a pretty well equiped machine shop at his home five minutes from my house and I can use the equipment anytime he is there,I'm getting pretty handy on the mill.........

If nothing else, it does make your carb look "tricked out",,,,,gets a lot of ohhhhs and ahhhhs at car shows...........

David

Tom Kirkham · #3 (**permalink**) 02-06-2005, 10:04 PM

BTW if you cut off the air horn you will want to inscribe the list number on the side of the carb. This will save you some grief in the future...

DAVID GAGNARD · #4 (**permalink**) 02-07-2005, 04:12 AM

Good advise Tom..............did not do it with the first one and forgot the #,did it on all carbs after that.................

David

trularin · #5 (**permalink**) 02-07-2005, 04:53 AM

The amount of air flow is governed by the venturies.

Removing the choke section of the carb allows for air draft and a better flow to the venturies.

People remove the choke section to allow clearance and to improve the ability to pull air from everywhere as David mentioned.

You can simply purchase a carb section that does not have the choke section from Holley or some third party supplier.

It is an easy swap and may take up to an hour to complete.

May I suggest you secure a new section without the choke and keep the old one in case it doesn't work well for you. My car likes the choke when it's cold outside, but it loads up a little if it isn't allowed to reach running engine temps.

HSSS427 · #6 (**permalink**) 02-08-2005, 09:27 AM

I've actually got the carb apart for a re-build, so it's a good time to do the surgery. However, the best idea might be to just buy the new throttle body. Keeps those nasty metal bits out of the garage and me from screwin' up something. Of course, I'll have to see what the fiscal damage is on that new body.

Have any of you guys been able to notice, or verify on a dyno, any improvement? I've got a turkey pan on it, so I'm limited on the filter size as well and wondering if taking the horn off will help in that regard as well.

Trularin, BTW, the carb is chokeless, so all it has is the horn and no plate so not much help with cold starts. I've just been setting the idle screw 2 turns faster and letting it run till it's warm, and then reducing the idle back down.
Thanks!
Scott

niles · #7 (**permalink**) 02-08-2005, 03:43 PM

HSSSS427;
I recently converted a 750 over to a Proform centerbody($95), it's basically the same center bode as on the HP,
these have removable airbleeds, etc. I found that useful in leaning out the idle circuit to reduce low speed fouling. they advertise 40-50hp increase. My results with a 393C stroker is that it runs some better everywhere, power is same or maybe a little better below 3K, from 4-6K, the 50 hp increase is a joke. I know I'm exaggerating but it seems like at least a 100 more hp! Before the engine was very strong is the 50-75 mph range, now it's down right scary with occasional wheel spin and I'm running a 3.08. A speed shop I use said it's the most positive item he has ever sold, NO ONE has ever been dissatisfied and all are tickled pink and that never happens in the parts arena.
gn

HSSS427 · #8 (**permalink**) 02-09-2005, 01:21 PM

What model carb did you use the Proform with? I saw these at JEGS, but I have a 4150 model #9379. Didn't see this specific model listed so wondering if the Proform main body will work with the other parts of this carb? Sounds like a pretty cheap price for a lot of horses! Did you change anything else out or just keep the same bowls, floats, throttle plate, etc?
Thanks!
Scott

niles · #9 (**permalink**) 02-09-2005, 02:55 PM

I converted a 750 3310 holley. They have centerbodies for double ppumpers also, but they are different and not interchangable. You use the same throttle body and bowls.
Look up Proforms web site.
I bought mine from fuel technolgies (same price as Jegs & could talk to carb experts) sand they were real helpful; they can machine your body to made a 4 corner idle adjustment and other trick. Just give them a call, they were real helpful with me and threw in a handfull of different jets on each side for nothing
gn

sllib · #10 (**permalink**) 02-12-2005, 05:05 PM

Scott;
Have you considered a K&N Stub Stack? It will give you about the same result as machining the choke horn for MUCH less money.
Bill Stradtner

HSSS427 · #11 (**permalink**) 02-12-2005, 07:43 PM

After Niles 100 hp reference, I ordered the Proform, but thanks for the idea Sllib. If this doesn't work, I'll send it back and try that.

Right now the catch is the 4150-9379 has an older style mechanical linkage where the cam actually rides on a shaft that is cast into the side of the main body. Looks like I will have to change to the newer style secondary linkage that doesn't connect to the main body. I think I'll probably just throw down on the Proform billet base plate while I'm at it. That would put in for about $250, and keeping the old bowls and metering blocks.

Also dropping the jet sizes from 68 to 67 on the primaries and 81 to 80 on the secondary side. The last dyno run I had the guy doing the run suggested I needed to lean it out some. Will dial it in on the dyno next run. Also changed the accelerator pump shooters to a larger size per his other suggestion, and will refine this on the dyno as well.

I've kind of broken the cardinal rule as I've now changed multiple stuff (the carb, changed the advance, and put in new parts on the distributor) and now will go back to the dyno with no idea which of these things contributed what to any changes. Well at least all are relatively easy to mess with during the runs to see what impact they have. Will let you know when I get that far.
Thanks!
Scott