Boring A intake for B carb....

[Bob-A]

When you enlarge the carb intake bore on the "A" manifold for the "B" carb. 1) The new diameter is equal to the "B" carbs upper body intake hole
{correct terminology?}? 2) How far do you bore: all the way or only for a short distance? 3) For a bore diameter I come up with 1 & 5/16ths inch.
Is this correct?

In the near future I hope to put a Snyder 5.5 head on my '29 roadster and I think a "B" carb would compliment it.

Thanks in advance for any advice.

Bob-A

[Dave in MN]

The primary passage could be enlarged all the way into the secondary passages.

I have a couple pictures with comments on my website. Look on the "DIY Help" page for the selection "Intake manifold enlargement"

Click on the link below and give it a little time to load...


http://m.www.durableperformance.net/...doc.3.5.11.pdf

Good Day!

[Tom Wesenberg]

Originally Posted by Bob-A

When you enlarge the carb intake bore on the "A" manifold for the "B" carb. 1) The new diameter is equal to the "B" carbs upper body intake hole
{correct terminology?}? 2) How far do you bore: all the way or only for a short distance? 3) For a bore diameter I come up with 1 & 5/16ths inch.
Is this correct?

In the near future I hope to put a Snyder 5.5 head on my '29 roadster and I think a "B" carb would compliment it.

Thanks in advance for any advice.

Bob-A

Since they are two seperate operations independant of each other, I'd do the head first and drive it, then decide if you think you need to do more. You might find the head alone is fine.

[montanafordman]

Originally Posted by Tom Wesenberg

Since they are two seperate operations independant of each other, I'd do the head first and drive it, then decide if you think you need to do more. You might find the head alone is fine.

I can't resist... Forget the fact this is a commercial - I still think its funny. ( I don't have AT&T BTW)

"More is Better"


Back to our regularly scheduled programming... I have been thinking of doing this also with my new motor. I've read up on the concept and I'm deciding whether or not to take it slow and ream it myself or take it to a machine shop and have my A manifold bored/drilled out.


-Aaron

[msmaron]

Call Renners Corner, they did it for me for 20.00 and only bore and taper about 2 inches in because of the way they want the air to flow.

[BRENT in 10-uh-C]

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Originally Posted by msmaron

Call Renners Corner, they did it for me for 20.00 and only bore and taper about 2 inches in because of the way they want the air to flow.

I doubt a dyno would show much performance difference between your manifold and a stock A manifold.

.

[Fred A]

It is hard to imagine why the Ford engineers changed the shape of the intake. The offset angle and the vacuum tap relocation were needed, but the flat top is a wonder to me. Could the B intake flow better than a bored A? Interested: Fred A

[Purdy Swoft]

A taper at the manifold flange where the carb mounts will help.The ones that I've done was with adjustable reamers. I ream the runner from flange to where it meets the curved area. The model A manifols are smaller in the curved area and where they meet the port area on the block. A reamed model A intake is better but still not as good as the B intake. The B intake causes problems with choke alignment and most just go with a reamed or bored model A intake instead. Every little bit counts and it all works together.

[Purdy Swoft]

Originally Posted by Fred A

It is hard to imagine why the Ford engineers changed the shape of the intake. The offset angle and the vacuum tap relocation were needed, but the flat top is a wonder to me. Could the B intake flow better than a bored A? Interested: Fred A

Fred, free tip here!!! The inside of the B intake is larger, not just the runner from the flange but all the way to the intake ports on the block. The flat top on the B intake better breaks up and distributes the mix to all cylinders rather than mostly to the front two cylinders. The flat top B manifold is one of the reasons that the B engines run smoother, Better fuel distribution to all of the cylinders.

[H. L. Chauvin]

Hi Bob,

FWIW:

In all of the different Model A opinions expressed today & in the past, and in all of the numerous different Model A performance religions believed in, one (1) Model A Faith we can hang our hat on is what is often written about, e.g., the Model A religion preached through human "experience" after one uses a fully "calibrated" Dynamometer as a mechanical Diety to express the truths for improving Model A performance. Reply #3 & reply #6 appears to echo this concept.

A few years ago, in speaking to Mr. Ron Kelley on increasing Model A engine performance he casually mentioned what most race car enthusiast are aware of, i.e., "Porting".

He mentioned that through experimentation he found in using his dynamometer that the first & most inexpensive & functional method to gain horsepower on a Model A engine was simple "Porting".

For example, he instructed me to first:

1. Use one's finger to "feel" inside the engine block for cast iron sharp edges, i.e., inside the intake & exhaust ports, to feel for roughness & sharp casting edges and to carefully & slightly ease these sharp turns & surfaces with a Dremel tool into smooth surfaces but being cautious not to cut into the engine's water jacket.

2. Do the same with the inside surfaces of the Model A intake manifold.

3. Remove the sharp lip under all valves & slightly round same, & slightly round tops of all valves to eliminate sharp turns which can create flow turbulence.

4. Check smoothness of the carburetor venturi & top opening of carburetor.

5. Do not allow the carburetor to manifold gasket protrude into the intake opening & cause turbulence instead of allowing unobstructed smooth flow.

6. After doing the above, he mentioned one can obtain maximum performance out of a standard engine or later for example, maximum performance out of adding for example, a high compression head, a B carburetor, and or a higher lift cam.

7. The speed of air flow & liquid flow depends greatly on smooth surfaces & smooth changes of direction. A good example is to watch fast moving water flowing in a very smooth concrete ditch as opposed to much slower water flowing in a rough earth ditch lined with 6" high grass; or watch the sloped angle in which water runs rapidly off of a metal standing seam roof as compared to slower flowing water dropping straight down 90 degrees off of the edge of a rough aggregate surfaced asphalt shingle roof with the same slope.

8. In my humble opinion, this was just one Model a guy's opinion, but tested with his calibrated dynamometer as opposed to sticking his head out of the window to listen to the exhaust difference; or holding one's hand out of the window to check the speed of the breeze while giving it the gas to test increased engine performance.

9. All I can mention is in following Mr. Kelley's advice with porting, and after installing a .330 cam, a Police Head, a B carb, & a B distributor, eyebrows raise when I take off from a red light.

Just hope this helps.

[BRENT in 10-uh-C]

I think there are some confusing statements being tossed. First off, it is my opinion that an oversized Model-A intake can be a just as good, --if not better than a stock 'B' intake manifold. I think much of it has to do with the size of the manifold draw tube. Originally a Model-A manifold was 1.000" rough-cast. The Model-B intake was 1.250 machined, ...and I personally take mine to 1.300" in size. Therefore if someone bores an 'A' manifold to a smaller size than the 'B' manifold, I think it is an accurate statement than an 'A' will not flow as well as a 'B', however if it has been bored larger, then it is at least equal if not better. A stock Model-A manifold is fine if it is reamed, --OR bored 2" above the throttle plate IF a Model-A carburetor is mated to the manifold, however when a 'B' carburetor is mounted onto one of those manifolds, this method has the opportunity to slow the velocity down in the larger 'B' venturi. Also, if the larger 'B' carburetor is mated to a smaller sized manifold, there is a potential for reversion which severely limits the air flow up the draw tube as there is constant air flow interference. Porting just for the sake of enlarging is usually a detriment if it has not been R&D-ed with a manometer to find where the change in airflow is most needed.

I did not want to touch on this earlier to avoid confusion but the cylinder head compression does not necessarily mean a larger intake size would benefit the engine. This larger manifold/carburetor is affected more by camshaft design. After a "larger" camshaft, ...the size of the intake valve affects the need for more fuel & air flow.

.

[quickchange]

Bob only . go to H/F buy stepped drill , extend the shaft , bore the A out . Simple cheep & works.

[H. L. Chauvin]

Also, in increasing air flow, smoothing out interior surfaces for faster fuel mix flow is often a controversial conversation & sometimes mentioned as a detriment to decreasing the blending of the fuel air mixture.

Appears like if some vintage manufacturer would have experimented with the liquid/air mix of a simple "Flit" gun; & attached an egg beater at the top end of the "Flit" jet to increase the air/"Flit" mix & blend ....... it could have told us a lot.

However, to try to better understand this liquid/air mix concept, in thinking back, many may remember how the mosquitoes dropped dead without an added egg beater.

[H. L. Chauvin]

Mr. Brent is correct in that this B vs. A intake is a deeper subject than one can imagine.

In his reply no. 11 above mentioning a B vs. an A intake diameter, without thinking, if one is quickly asked what is the difference in cross sectional area between a 1" pipe & a 2" pipe, many slightly uninformed would say the 2" pipe has double the area of a 1" pipe; however, a 2" pipe has (4) times the area of a 1" pipe.

So when Mr. Brent is mentioning using a 1.30" diameter intake in lieu of a 1" diameter intake, the cross sectional area of the 1" intake is increasing from about 3.14 square inches to a whopping 5.30 square inches, (about a 70% increase in cross sectional area), which also directly influences the velocity of the air/fuel mix where the velocity of the fuel/air mix with the 1.30" intake decreases theoretically approximately 70%.

Bottom line may be thought of as a larger diameter length of pipe upstream & a smaller diameter length of pipe downstream has greater forced flow at the end than that of a smaller diameter pipe upstream with a larger diameter pipe down stream; however, keep in mind that the lengths of each of the pipes are a major concern as well as the interior surface friction inside each of the pipes in which both length & surface friction can affect the volume of flow at the end of the pipe.

[Bob-A]

Holy-Moly!!..... I just wanted to know which way is best to set up an
"A" intake for a "B" carb. I was a Water PLant Operator for 30 years and
when H. L. Chauvin mentioned "pipe diameter.....length & surface friction..." I thought I had a flash-back.....

Thanks everybody for your learned input. The experience & knowledge
you guys have is invaluable to me and I'm sure other people of the board. I truely enjoy reading everybodies piece of wisdom and can not wait for the next one. Thanks again.

Bob-A

PS: Dave in MN has a good example of how and what to do on his
website. I think that is the direction I'll go.

[Tom Wesenberg]

Originally Posted by Fred A

It is hard to imagine why the Ford engineers changed the shape of the intake. The offset angle and the vacuum tap relocation were needed, but the flat top is a wonder to me. Could the B intake flow better than a bored A? Interested: Fred A

If the flat top is hard to figure out, then give this one a try.
This was found at an auction about 50 miles north of me about 20 years ago. I don't know who owns it, but I took this picture at the national meet at Kansas City about 15 years ago. It sure looks like someone went to a lot of work to make a nice one off experimental manifold. Notice the 2 brass carb jets to let in a small amount of air to mix with the flow.

[Pete]

What with all this talk it probably won't be long before someone will do some actual testing on a flow bench to see what is what.
That's what happened with the flathead V8.
Bigger is not always better when using a flow bench.

[Mike V. Florida]

Originally Posted by Tom Wesenberg

If the flat top is hard to figure out, then give this one a try.
This was found at an auction about 50 miles north of me about 20 years ago. I don't know who owns it, but I took this picture at the national meet at Kansas City about 15 years ago. It sure looks like someone went to a lot of work to make a nice one off experimental manifold. Notice the 2 brass carb jets to let in a small amount of air to mix with the flow.

Idon't think that's a "one off". I think I saw it in the unauthorized accessories book (I don't have it here) but I think they called it a "bat" manifold.

[Terry,NJ]

FWIW! I've bored a couple of A manifolds and with an A carburetor, there is a noticable improvement. A quick description how I did it, goes like this; First make a plug (at least two inches long) with a 1/2, Chuckable shank. This must be fairly close to the hole Dia. Polish some of the roughness out of the hole. This plug "finds" center of the hole. With the plug in the drill chuck and the manifold, Clamp, lock it down, whatever, replace the plug with a 1.250 drill that cuts oversize. Drill to full length of the hole. When the drill reaches bottom, you're almost done. Take the manifold off and polish the bore with a 1 1/2" flap wheel. At this point, I like to polish any reachable surfaces. Reassemble and enjoy! Total cost in time? About two hours. A word of caution! Be absolutely sure you've followed the hole. Don't walk the drill off and break through the sides, they're rather thin. That's why I make the plug so long.
Terry

[Logan]

I personally wouldn't bother with a B carb on an A manifold that's bored out. It's a lot of work and money spent for minimal performance enhancement. You get like 1-3 hp difference. I doubt it would even be much noticeable. Maybe with more port work in the block you could get more out of it. But that's just more time and money to then just slap a B carb on it. If you want more performance, a down draft (like a stromberg or a weber) or dual updraft manifold would be better.