Stromberg Big97

[35fordtn]

I recently acquired one of the "new" 250 cfm Big 97's. I have used the new stock 97's, but I thought about putting this thing on the engine I built for one of my vehicles. It will have a single stock 59A intake.The engine is a stock 59A with a mercury crank .100" over stock heads, and stock cam. Do these run fine like the stock 97's out of the box, or do they need to be re-jetted?

[JM 35 Sedan]

I would think Uncle Max could fill you in on all the details on how the big 97 should be set up for your particular application.

[Tim Ayers]

I'm curious about these as well.

[Ol' Ron]

Are the throttle bores in the intake bored out to match the carb??

[tubman]

Originally Posted by Ol' Ron

Are the throttle bores in the intake bored out to match the carb??

I was just going to ask the same thing. I would think that almost doubling the flow (from 145 to 250 cfm) would be impossible without substantially increasing the bore. To get more mixture in, you either have to increase the velocity, which I would think is directly related to engine speed, or increase the area of the passage.

[35fordtn]

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"IF" I do use it, I intend increase the opening of the intake to match, likely taper the holes so there is still some structural integrity between the two openings.

[Jack E/NJ]

Use a tapered spacer instead. Jack E/NJ

[tubman]

Isn't the taper just a cosmetic touch? It may make you feel better because there is no abrupt "ledge" in the manifold, but isn't the ultimate limit the smallest cross-section in the passage? Sorta like a NASCAR restrictor plate; they're pretty thin, but they do the job (just ask the drivers). When I put a 2G on a Mercury manifold, I bore it all the way down and then blend the transition to the individual passages to the ports. I have no real way of measuring, but you have two passages going into four, and then eight, so there should be an increase in area. Perhaps a modified Mercury manifold (which I know will take the larger bore) or perhaps an overbored Ford manifold with a sleeve inserted.

I have a hard time believing that passages in a Ford manifold designed for 145 cfm would support anything even close to 250 cfm.

[deuce lover]

A good friend just bought a pair of these directly from Clive.When I spoke to him he asked what engine(FF stock bore & stroke) and cam Max 1 was being used so he would jet it correctly.Yes the the bores on the intake has to be bored or enlarged to match the carb base.As far as running out of the box we do not know as yet.

[Lawrie]

And ,you want be able to use an early manifold as the wall are not thick enough, I cut open a damaged 35 one and its way too thin, so I used a later 8ba one.
Lawrie

[KiWinUS]

Originally Posted by tubman

Isn't the taper just a cosmetic touch? It may make you feel better because there is no abrupt "ledge" in the manifold, but isn't the ultimate limit the smallest cross-section in the passage? Sorta like a NASCAR restrictor plate; they're pretty thin, but they do the job (just ask the drivers). When I put a 2G on a Mercury manifold, I bore it all the way down and then blend the transition to the individual passages to the ports. I have no real way of measuring, but you have two passages going into four, and then eight, so there should be an increase in area. Perhaps a modified Mercury manifold (which I know will take the larger bore) or perhaps an overbored Ford manifold with a sleeve inserted.

I have a hard time believing that passages in a Ford manifold designed for 145 cfm would support anything even close to 250 cfm.

Nascar no longer uses restrictor plates, haven’t for over a year. Now use tapered spacer. Personally I believe the advantages of the big 97 would only be at wide open throttle. To get the biggest bang for your buck you would want manifold opened fully not tapered down. I believe if you have to run tapered a stock 97 would perform as good.

[tubman]

Whether or not NASCAR still uses restrictor plates or not has nothing to do with the issue. When they did, they DID substantially cut down performance. I think that counting on a tapered spacer to solve the flow problem is "whistling in the dark". Get serious people, this is basic science.

[KiWinUS]

Originally Posted by tubman

Whether or not NASCAR still uses restrictor plates or not has nothing to do with the issue. When they did, they DID substantially cut down performance. I think that counting on a tapered spacer to solve the flow problem is "whistling in the dark". Get serious people, this is basic science.

Could not agree more:- nothing to do with the issue & Get serious!

[Jack E/NJ]

In fluid dynamic theory, tapered spacers (funneling flow) promote laminar flow for better flow velocity but reduced mixing. Restrictor plates promote turbulent flow for better mixing but reduced flow velocity. Again, In theory. In practice, it seems to work that way too as per the videos in the link below. I like the one with the big pair of jugs. 8^) Jack E/NJ



https://buildingspeed.org/2018/10/12...apered-spacer/

[tubman]

We are not concerned with flow characteristics here, but flow volume.

[JSeery]

Restriction over a short distance (such as a venture) has little impact on flow rate. But a restriction over a larger distance has a big impact on flow. The whole idea of increasing flow volume on a flathead is to open up the ports and try to smooth out the flow path. I don't see how an increase size in the carburetor throat without increasing the intake ports would be of much value.

[35fordtn]

My initial question was only based on the fact that I wound up with this carburetor for a trade toward labor. I was hoping to use it since I have it. If it does not "hurt" performance I will still use it even if it does not help.

[tubman]

Since you've got it, why not take advantage of the increased potential? I did a little simple math, and it looks like the area of the 8 intake ports is greater than the area of the two larger throttle bores. From everything I've seen, if the intake is bored out all the way down, the area of the intake passages increase as they get closer to the intake valve. A Mercury manifold properly bored with the third mounting stud added should work well. I know they do with the small base 2G (which are nominally 275 CFM).

If you don't want to go to that much trouble, I would think that it would work as well as a standard 97 on a stock intake. In that case a tapered adapter or modified manifold would probably be of value in smoothing out the flow.

[JSeery]

Don't see how it would hurt to give it a try.

[Jack E/NJ]

Of course, volumetric flow. What do you think we're talking about? Did you watch how those big pairs of jugs volumetrically flow? Jack E? NJ