Stromberg 97 or Holley 94?

[jeepguy1948]

This question is in tandem with the questions I just asked about manifold vacuum: I am working on a ‘51 F-1 for a friend and it now has a Holley 94 on it. I have a Stromberg 97 on the shelf, would that be better? I doubt that the minuscule difference in the bore would have an effect??? The motor is a 255 Merc. With a “3/4 Race Cam” (whatever the h**l that means). If I stick with the 94 what jets and power valve would be best? If I install the 97, what jets and power valve? Thanks!

[tubman]

Please read my response to your other post. To be frank, I believe you're in over your head on this one.

Thiis is not the time to be talking "jets and power valves". Get back to basics first.

One important piece of information that is missing is : "What distributor is currently on the engine?".

It makes all the difference in the world when discussing carburetors.

[bobH]

I'll be interested in what the experts say on this one. Tubman's info is good. If I had to choose between the 94 and 97, obviously choose the 94, if a load-a-matic is being used. But, original for a 255? And, a 255 that has been messed with (cam)? What say the experts? How about a converted distributor, and a little 'more carb'. I don't think it's ever going to run good with what he has said, so far.

[tubman]

You are aware, I am sure, that the the Mercury's of that era used the Load-A-Matic system, even though the Holley carburetor they used was very different from a 94.

Anyone who is not cognizant of the various ignition advance types used during this time is at a huge disadvantage when attempting too tune one of these engines.

[Bored&Stroked]

Just to add . . . the "load-a-matic" system is primarily related to the distributor and how it handles advance (and its interaction with vacuum from the carb).

In order for the distributor to advance/retard, it needs the proper vacuum signal form the proper intake/carb system. While the stock system works quite well (if left stock), the minute you start swapping out components on the carb side (number of carbs, types of carbs, etc) - then you have to consider that the distributor may no longer receive the correct vacuum signal - so your advance curve is all screwed up.

Now, if you change the distributor to one that utilizes mechanical advance (like a Mallory unit), a magneto, etc - then it is no longer dependent upon a very specific vacuum signal. Its advance curve is strictly based on RPM.

So, this is why TubMan is letting you know that you have to consider (and understand the details of) the WHOLE intake/ignition system when making choices related to carbs, manifolds, the number of carbs, distributors, etc..

[jeepguy1948]

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I just wrote a long reply on the vacuum thread which I’m not up to re writing here so please refer to that. So, motor is not stock, it is a period correct mild hot rod, it is a Merc motor 30 over, it has Edlebrock aluminum heads, that “3/4 race” cam I mentioned earlier, tube headers, dual 1.75” exhaust, original distributor with a Pertronix module and coil (timing is set at 28 degrees total). Given that the owner is not concerned about keeping things stock, and I have a “fresh” 97 on the shelf (the reason that I am asking about jets and power valves is that the 97 was tuned to my ‘28 Model A), the 94 was rebuilt a few years ago but never reinstalled and I have no idea what jets or power valve it has in it. Given the motor I have described, I would assume that either one of the 2 carburetors would need some changes done to it. We are looking for the best performance but with an emphasis on driveability. So please, give me some guidance on which way to go and if there are any other things I should be looking at. I am here because this is where the experts are, I am a gear head but not a V8 expert looking for some help. Thank you

[jeepguy1948]

BTW I am aware that the distributor has only vacuum advance. I have installed a new vacuum diaphragm.

[jeepguy1948]

My apologies, I tend to ramble.

[jeepguy1948]

My “Flatheads” are a ‘28 Model A Roadster Pickup, and a ‘48 Willys Jeep (CJ2A)

[flatjack9]

Originally Posted by jeepguy1948

I just wrote a long reply on the vacuum thread which I’m not up to re writing here so please refer to that. So, motor is not stock, it is a period correct mild hot rod, it is a Merc motor 30 over, it has Edlebrock aluminum heads, that “3/4 race” cam I mentioned earlier, tube headers, dual 1.75” exhaust, original distributor with a Pertronix module and coil (timing is set at 28 degrees total). Given that the owner is not concerned about keeping things stock, and I have a “fresh” 97 on the shelf (the reason that I am asking about jets and power valves is that the 97 was tuned to my ‘28 Model A), the 94 was rebuilt a few years ago but never reinstalled and I have no idea what jets or power valve it has in it. Given the motor I have described, I would assume that either one of the 2 carburetors would need some changes done to it. We are looking for the best performance but with an emphasis on driveability. So please, give me some guidance on which way to go and if there are any other things I should be looking at. I am here because this is where the experts are, I am a gear head but not a V8 expert looking for some help. Thank you

If you have a stock distributor you must use an 8BA style carb with the center(venturi) port. Manifold vacuum will not provide the correct signal to the distributor

[33ratrod]

My understanding is the 97 does not have the right vacuum for the stock load a magic distributor only the 94 has that. Correct?

[1948F-1Pickup]

Originally Posted by 33ratrod

My understanding is the 97 does not have the right vacuum for the stock load a magic distributor only the 94 has that. Correct?

See this thread, particularly the #5 post.....

https://www.fordbarn.com/forum/showthread.php?t=277149

[tubman]

It gets a little complicated. It is my understanding that some aftermarket companies (Western Auto) made versions of the 97 that had the Load-A-Matic port. Who knows? Maybe even Stromberg did. So there may be some out there. Conversely, there are many models of 94's without the port, with pre-'49 Ford products being a prime example.

What it boils down to, does a carburetor (either type) have the port or not? If so, it will run a Load-A-Matic.

[19Fordy]

Not sure if this will help but here is the stock 8RT intake and Holley 94 with stock #51 jets that I ran on my 296 cu. inch 1950 Merc with OFFY heads and an Almquist 3/4 cam many years ago. I used the stock Load-a-matic distributer and it ran fine but wasn't fast.

Here's an excellent video that explains all the Ford 2 barrel carburetors and the use of the Load-a-matic dist.
https://www.bing.com/videos/search?q...tail&FORM=VIRE

[Bored&Stroked]

Flatjack9 has it right . . . he said it a lot more succinctly than I did. On the stock distributor, you can change the points to Pertronix, you can change the diaphragm, etc. - but it is still reliant upon the specific venturi port signal to create its advance curve.

When you move away from a stock engine (cam, heads, intake, carb, etc), then you have no idea as to if or when the distributor is getting the correct signal, to set the advance where it needs to be. This means the engine will run poorly - at least some of the time (usually because of too little advance).

So, the solution is to get rid of the stock distributor - and go with one that is designed to be used in your updated engine --> this could be a special late-model chevy distributor converted for flathead use by Charlie NY (or others), it could be a Mallory distributor with mechanical advance only (think back to the flat-tops everybody ran), it could be a magneto, etc..

The bottom line is that it needs to have a mechanical advance mechanism to set the initial curve. It is also possible for have a vacuum advance setup in addition to the mechanical one (like on a late model chevy dizzy) to work with the flathead - to achieve better mileage under low-load conditions. Usually manifold vacuum is used with these late-model distributors - not venturi vacuum. This solves the problem of matching the carburetor and its venturi vacuum characteristics with your load-a-matic distributor.

Guys like Charlie NY will modify a Chevy distributor to limit the advance to meet our flathead requirements and may or may not recommend a vacuum advance cannister in addition to the mechanical advance mechanism.

Me, I tend to run original Mallory flat-top distributors or magnetos.

[jeepguy1948]

I am aware that there are 2 different types of vacuum advance. The far most common way is to use manifold vacuum which drops as the motor load increases (this type is usually used in conjunction with centrifugal advance to back of on they timing at light load such as cruising down the freeway, this is primarily for fuel economy). Then there is the type that the 94 has which is what I have always known a “Venturi” vacuum which goes up as throttle is increased. This is not unique to a Holley 94, there have been many engines over the years using this system. My mistakes were #1, in assuming the “Urban Legend” that says all V8’s came with a 97 was true (obviously it’s not). #2 assuming that the 97 also had a Venturi vacuum port without looking (many carburetors do, even if it’s not used). #3 is the confusing one, and that is that with the old vacuum gauge I was using vacuum seemed to increase using the wiper port. I still don’t know for sure what’s going on there but I will use a different gauge on Monday.

[jeepguy1948]

So, in the end, the simple answer is that a 97 could not be used without changing the distributor as well. Just to be clear, we are not married to the stock distributor. If better performance/drivability would be had with the 97 we would change the distributor. We even have a Mallory dual point on the shelf.

[Bored&Stroked]

In the end, you can run a Stromberg 97, swap the distributor and be in good shape. I'd start with a stock jetting of 45's, though it will probably need more fuel than that - maybe go to 48's to start. There is no way to know on the mechanical power-valve (what to run), so I'd start with a stock one. You may need more fuel than it delivers under load - but you won't know until you drive it. I tend to use an O2 meter in the exhaust to see what my AFR is under various load conditions.

Also, I usually set the acceleration pump squirter rod on the outside position (on the linkage) - to give more of a squirt than the inner position.

Best of luck . . .
B&S

[Ol' Ron]

B&S has covered this quite well, and the engine mods are conservatives for street. My thoughts would be to convert to a merc intake with a 2GC carb. This would work well as a street carb with all the air the engine can use, However, tuning the engine will take some doing. Including a AF meter and adjustable Machanical advance ignition. and 28 Degs advance might be too much at the wrong RPM. This is where most people make there mistske. Once they get the right parts, they don't know what to do with them.
Gramps
PS for some people out there the 1 1/16 late Holley (94) and load a matic distributer will solve allot of tuning problems, but when you change the cam, your in a different world.
G

[1948F-1Pickup]

Originally Posted by jeepguy1948

So, in the end, the simple answer is that a 97 could not be used without changing the distributor as well. Just to be clear, we are not married to the stock distributor. If better performance/drivability would be had with the 97 we would change the distributor. We even have a Mallory dual point on the shelf.

Already answered this in post #12 above.

The Stromberg 97 1-1 has the correct vacuum port that supplies the load-o-matic distributor. That's it. It's the only one. #7 in the diagram below is the magic port for the load-o-matic.
























https://www.stromberg-bulletin.com/1...h-vacuum-port/