Modified Zenith Carburetor

[modela-carb]

Brent Terry and I have been working on a way to modify a Model A carburetor to boost its horsepower to about the same as would be gained by using a Model B carb. The changes would be internal and not change the outward appearance of the carburetor. It would be sold with a modified intake manifold.

We think we've got a good design worked out but before we go to the next steps of machining and testing, we thought it might be worthwhile to ask the community what you think of the idea..would you purchase the carb/manifold, and, while no price is known, what range would put one in your car?

[newshirt]

Jim,
Can you state the horsepower difference between A and B carbs?

[Joop]

And show some pictures how it is going to look like.


..

[Kurt in NJ]

Would I still get the same fuel mileage(20-23)---along with the same low exhaust emissions 1-2%CO, less than 100PPM hydrocarbons)---and increase my top speed from 67 to 70+???

[fordfixer]

I think this is a great idea. I'm sure if the price is reasonalbe I would purchase one or two.

[BRENT in 10-uh-C]

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Originally Posted by newshirt

Jim,
Can you state the horsepower difference between A and B carbs?

Well, all of this is still in the infancy but originally Ford advertised his Model A engine at 40 horse, and his 'B' at 50 horses. Theoretically that additional Hp came from a larger carburetor & manifold, a cam that had increased lift (.287" to .304"), and had a notch more compression. Based off of some dyno testing by Bill Stipe, a B carb on a B manifold will make a gain of anywhere from 3 - 5 additional horsepower depending on the combination of the engine. The huge limiting factor in Model A engine performance is breathing. Many of us already install a higher compression head, and many of us opt for Bill's IB330 or IB340 camshaft with favorable results. This would just be something to compliment what we are already using.

I will be the first to say this carburetor might not be for everyone, and in a nutshell all this carburetor will be is a larger venturi and throttle plate inside of a stock-appearing Zenith Model A type carburetor. I will be quick to agree that if someone wants to install a Weber carburetor or a pair of Stromberg 97's, they can make more power. To some, that is their goal, but for me I prefer something like this to help preserve aesthetics.

While Kurt's question may initially seem arrogant, it really is not in my opinion because as I eluded to above, this type carburetor is not for everyone. For me, I could use this carburetor in fine-point judging and score enough points to win a 'Henry' in Wednesday judging, and on Friday's Mandatory Tour if I used those "hidden internal goodies" and coupled that engine with a 3.54 or 3.27 rear end gear ratio, I can theoretically Tour with my Fine-point Model A with them fellars who have Mitchell overdrives and down-draft carburetors on theirs, ...and never get left behind.

For me it is not about the ability to be able to drive at 60 mph, ...its having the capability to stay out of everyone's way while driving up an incline or hill at 40 mph in heavy traffic. In other words, if I have 50% more power in the mid-range, I have a 50% better chance of keeping up with traffic.


.

[MrTube]

Come on now, you know practically everyone is only going to select the lower price range.

Would this also be modified with the float bowl venting through the air filter?

[modela-carb]

MRTube

No, As Brent pointed out, the carb would look absolutely stock with changes only to Venturi, throttle plate, and intake manifold.

[MrTube]

Hmm, I would be more after an aluminum or zinc version of the Zenith with internal venting from the float bowl to the air cleaner. It could still look like the original, but at the same time be modernized internally. You know, better flow, better metering and so on.

At the same time I suppose others might be against what I want. Just wanted to put my thoughts out there, respectfully.

[Pat Martone]

Yes, I am interested in this new carburetor/intake manifold combo because it will provide a small boost in power without externally noticeable changes. I am not interested in higher speeds, but I do want the ability to keep out and stay out of other people's way and avoid annoying people with my sluggish antique car. Please keep me posted. Thanks.

[Jamie86]

Yes, I think this is a great idea. Especially, if you could get it preform like the Model B carburetor. It would depend on how much it would cost, though. It always comes down to money.

[Flathead]

I think you could sell them. More performance with a stock look is appealing, and as you stated, good from a judging standpoint too.

[SteveB31]

Great idea Brent!!!!! Keep the price right, make it look stock and you will be very surprized at how many you would sell.

[JoeWay]

How about the people who already have well-restored A carbs that run great? Will you offer to modify their upper body?

Joe

[ctlikon0712]

It all comes down to cubic dollars! lol

[FL&WVMIKE]

I think that it will affect your gas mileage.
I just put a S&S carburetor on my Harley. You had better hold on when you crack the throttle, but my gas mileage went from 50 mpg to about 30mpg. I'm thinking of taking it off.
MIKE

[SAJ]

Great Idea guys. I lay in bed at nights thinking about how I could improve intake breathing myself.
I have all the machine tools, but it is still not an easy job in terms of time spent. I would buy one and, including the the modified manifold, pay in the higher range too.
The only other carb mod I would consider is "in period" dual updraft zeniths. Stretching originality, I know, but also very difficult for us right hand drive guys.
I already have a full-flow oil filter, pressure guage and air cleaner in the space left next to the steering column, so there's precious little room for dual updrafts too. I could not use an in-line set up like Purdy Swoft's, which looks really nice. It would have to be a crossways, side-by-side one as posted recently.
Once again, a great thought. I too want to avoid blocking traffic on hills
SAJ in NZ

[modela-carb]

Originally Posted by JoeWay

How about the people who already have well-restored A carbs that run great? Will you offer to modify their upper body?

Joe

Joe, It's early days yet, but I don't see any reason why not...keep in mind you'd need the modified manifold too.

[1931 flamingo]

What is being done to manifold?? Will it externally look original? Exhaust hook up as original?? Could and original manifold be "opened" up to match new venturi size??
Paul in CT

[JoeWay]

Originally Posted by 1931 flamingo

...Could and original manifold be "opened" up to match new venturi size??
Paul in CT

Paul,

Yes indeed. I've opened up mine to match a B carb. Dave in MN has written up a great tutorial on the job. See this link.

It can be done with just a machine vise instead of Dave's fixture, but takes a bit longer to set up. It's very important to be aware that the carb mounting flange is NOT at right angles to the throat of the manifold. I used a drill bit that just fit into the throat for alignment, then changed to the larger bit for the overbore.

Joe

[1931 flamingo]

JoeWay: Thanks for the link. I knew the A manifold could be opened up for the B carb and that the attaching needed to rotate a bit. Is the "new" carbs venturi area going to be as big as a B or larger??
Paul in CT

[1928Pickuppain]

i would buy one i like the idea off a little more powere

[BRENT in 10-uh-C]

Originally Posted by 1931 flamingo

What is being done to manifold?? Will it externally look original? Exhaust hook up as original?? Could and original manifold be "opened" up to match new venturi size??
Paul in CT

As Joe said, many of us have been boring (or drilling as David is doing) the 'A' manifolds. Originally the Model B was 1.250" and I do mine at about 1.300" on the draw tube.

This project is something that I have been comptemplating for several years now as I would like to install the proper looking manifold and carburetor. Joe, to answer your question about using a good running carburetor, while that is a possibility, remember that the bowl will need to have machine work, and the jets will need to be re-flowed because with more air comes the need for additional fuel. The only thing that I tend to think would be different than Mike's S&S carb that he installed on his Harley is that with a modified 'A' carb, we would still be able to use the GAV to lean out the fuel mixture to increase the fuel mileage. Granted horsepower will suffer with less fuel but it does kinda allow one to have their cake and get to eat it too.

[modela-carb]

Originally Posted by 1931 flamingo

JoeWay: Thanks for the link. I knew the A manifold could be opened up for the B carb and that the attaching needed to rotate a bit. Is the "new" carbs venturi area going to be as big as a B or larger??
Paul in CT

Paul, at this point, we're thinking same size as the B. There's a limit to how much metal can be removed safely and until we get further into the project we don't know what the final dimension will be.