A Performance Question Regarding NH Carbs

Topics Last Day Last Week Tree View    Getting Started Formatting Troubleshooting Program Credits    New Messages Keyword Search Contact Moderators Edit Profile Administration
Model T Ford Forum: Forum 2012: A Performance Question Regarding NH Carbs
Top of pagePrevious messageNext messageBottom of page Link to this message  By Dave Young in Mays Landing, NJ on Sunday, July 29, 2012 - 07:22 pm:

Is removing the choke plate and shaft from the NH carb a common old-time performance mod? It would seem that the engine would breath much better without that large restriction in the air path. I have yet to try it... but I'm on the verge. An external choke plate could be easily fabricated, like the ones on old outboard marine engines.

I recall reading in the Montana 500 rule outline that the carb inlet bore diameter will be inspected and must be of a certain stock size. Do they run choke-less carbs?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tom Carnegie on Sunday, July 29, 2012 - 08:20 pm:

Montana 500 carbs must be complete, including butterfly. The major restriction in an NH carb is the venturi, which is also controlled in the Montana 500.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bob Jablonski on Sunday, July 29, 2012 - 08:21 pm:

A better modification would be to use a 1912 Aluminum intake manifold, larger bore than the cast iron manifold that followed. Got one for you.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dave Young in Mays Landing, NJ on Sunday, July 29, 2012 - 08:31 pm:

Bob,
I would like to try that. It's always surprising how much better she goes with the top down. Hey, l had to rotate my tires today because they are showing wear... ain't like I drive 'er much ! We only did 1,100 miles this month.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kenny Edmondson, Indianapolis on Sunday, July 29, 2012 - 08:56 pm:

Dave, the area where the air goes around the choke is still larger than the venturi area so no performance will be gained by the removal of the choke. I always liked the little aftermarket swirl type devises that was accessories for T's as soon as the air stream hit the choke or throttle plate, the swirl motion would be lost.

As Bob said above, use a large bore aluminum intake and a straight thru carb.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ricks - Surf City on Sunday, July 29, 2012 - 10:19 pm:

Better yet, get a real carb like a Stromberg OF or Schebler FA. Those puddle carbs are limited on their best day. If you're driving that much, the OF will pay for itself in fuel savings.

rdr


Top of pagePrevious messageNext messageBottom of page Link to this message  By Don Lyon, PDX, OR. on Monday, July 30, 2012 - 01:00 am:

The choke plate and shaft are the same size as the throttle plate and shaft so there won't be any increase in air passage.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Norman T. Kling on Monday, July 30, 2012 - 11:26 am:

How are you going to start the engine without the choke? You need some kind of choke to get it primed for starting. After it is running you don't need the choke.
Norm


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Patrick on Monday, July 30, 2012 - 11:41 am:

Norm beat me to it. There is very little restriction with the spring loaded butterfly valve completely open as it is when not being used to choke the engine, so why remove it. My engine was recently completely overhauled and runs better and more smoothly that it ever has, yet, I still must choke it prior to starting or I would never get her started. The purpose for the butterfly valve is to close off the flow of air to suck in sufficient quantities of gas to get the engine started. If I followed your idea and took out the butterfly choke valve, it may run as good as with the butterfly valve in, but I would never find out because I would never be able to get it started. One may try to re-engineer equipment, but should think it through and consider that something would not have been designed in and kept as part of the design for a century, if it did not serve an important function. Jim Patrick


Top of pagePrevious messageNext messageBottom of page Link to this message  By Fred Dimock, Newfields NH, USA on Monday, July 30, 2012 - 12:38 pm:

Norm & Jim -- To choke a car without a choke plate just ask your wife to hold her hand over the carb inlet for a short time. :-)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bob Jablonski on Monday, July 30, 2012 - 12:54 pm:

Sounds like you'e going fast enough wearing out those tires,,,,,,,LOL !!

I'll drop ship to you tomorrow along with manifold & carb gaskets


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Patrick on Monday, July 30, 2012 - 01:02 pm:

Fred, She can't do that AND crank the car. :-)

Dave, In the below diagram, A points to the venturi Don is referring to.



Top of pagePrevious messageNext messageBottom of page Link to this message  By Erich Bruckner, Vancouver, WA on Monday, July 30, 2012 - 01:19 pm:

It is also worth checking to be sure the choke butterfly is straight to the in-flowing air. I have seen some that rested a bit canted. It is also worth taking both butterflies out temporarily so the internal passage can be smoothed a bit (remove steps) as well as enlarged a small amount. Makes the larger intake more useful. My swayback NH treated as above runs stronger than the straight through NH ever did and starts easier too.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Patrick on Monday, July 30, 2012 - 01:26 pm:

The venturi in the NH, like a venturi in a sandblast nozzle is there to increase the velocity of the airflow. Be careful about enlarging a venturi, as, you might actually slow down the passage of air, thereby disrupting the proper fuel to air mixture ratio as it is being pulled into the air intake. Jim Patrick


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kerry van Ekeren (Australia) on Monday, July 30, 2012 - 05:31 pm:

Jim,
that's the beauty of the T carby, an adjustable main jet to balance the mixture ratio, my NH straight through venturi is reamed out another 1/8th of an inch, that has given me more torque than when I tried a Z head.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Erich Bruckner, Vancouver, WA on Monday, July 30, 2012 - 06:20 pm:

I know my ear from a hole in the ground but just barely so it is only my guess, but, I think the sway back NH is more forgiving of venturie enlargement than the straight through due to the dip creating an airfoil type effect whereby the air at the outer edge of the curve (i.e. the bottom of the dip)has to speed up to get around the corner, thereby giving the desired effect at the point of the fuel puddle at the bottom of the dip. Is that the longest run on sentence or what?

Clear as mudd? I may be all wet on that assumption. Please chime in anyone who may know carb theory.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mike Robison on Monday, July 30, 2012 - 07:17 pm:

Keep the ideas rolling going guys, us Montana 500 guys need tricks!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dave Young in Mays Landing, NJ on Monday, July 30, 2012 - 09:51 pm:

Hey, the choke issue is no problem, cause my wife could hold her hand over the carb inlet while my girlfriend cranks it over !!!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dave Young in Mays Landing, NJ on Monday, July 30, 2012 - 09:54 pm:

Bob,
No rush on borrowing your manifold. I'll swing up and grab it sometime.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dave Young in Mays Landing, NJ on Monday, July 30, 2012 - 10:22 pm:

I am gonna do what Erich mentioned, but while the butterfly is out I'm do some test runs before putting the choke back in. My engine is freshly rebuilt by George King and runs great.

All of my systems are stock Ford, the water pump is sitting on a shelf, and the Ruckstell even came out this past spring. I just enjoy tinkering with these old girls and the carb restriction thing just crossed my mind.

Even though the throttle butterfly is the same size as the choke, l tend to feel that the affect of two items standing in the airway would have the same affect as having more elbows on a woodstove chimney pipe.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tom Carnegie on Tuesday, July 31, 2012 - 12:00 am:

I wouldn't get too hog-wild with smoothing out things. Some air flow issues are counter-intuitive. Bigger isn't necessarily better. Smoother isn't always better. The Spokane group has smoothed and hogged out and flow checked dozens of carbs and some of the best are bone stock ones.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dave Young in Mays Landing, NJ on Tuesday, July 31, 2012 - 06:08 pm:

Thanks Tom.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Cameron Whitaker on Tuesday, July 31, 2012 - 09:01 pm:

Here's my 2 cents worth (and that's all it's worth)

If it works fine and you start playing with it, you may wind up making it worse than better!

As I always like to say, "If it ain't broke, don't fix it, and if it works, don't touch it!"


Top of pagePrevious messageNext messageBottom of page Link to this message  By Erich Bruckner, Vancouver, WA on Tuesday, July 31, 2012 - 09:20 pm:

1. The stock NH works well.

2. There is a point at which "improving" it will become detrimental.

3. We can not be sure of the point at which this occurs.

Proceed at your own risk. Less may be more here. Henry did pretty well at making a well balanced machine in most regards. I may have gotten lucky with mine, but I am happy with the change in performance.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Fred Wicker on Wednesday, August 01, 2012 - 06:44 am:

Heres a Holley I picked up,intake has been ported also. Is this Holley a go-fast part?
Wick


Posting is currently disabled in this topic. Contact your discussion moderator for more information.
Topics Last Day Last Week Tree View    Getting Started Formatting Troubleshooting Program Credits    New Messages Keyword Search Contact Moderators Edit Profile Administration