Anyone have any experience using 4 Weber 48IDA carbs on a 6/8-71? I've just procured a complete setup for a blower. Unit has been sitting for years and since I have zero experience with these carbs I'm asking input from those with experience. Unit has manifold to blower, 4 48IDA carbs (Italy), fuel line plumbed and all linkage. How should I proceed from the start. Unit will be installed on a 413ci SBM setup with a 6-71. Suggestions appreciated!!

Well it will look cool and if you have the linkage properly synchronized it should run pretty good. There are lots of books and articles on Weber carbs so dig in and do some research. They have a lot of tuning capability but you'll need to source some parts. The linkage is very critical. All 8 throttles have to be synchronized or else it will never run very well. I've worked on them just enough to know what a pain the linkage is. Hopefully your setup came with a well designed linkage. Take a close look at it and see if operates freely with all four carbs closed at idle and WOT at the same time.

Draw through (above the blower), or blow through (carburetors on the engine)?

it is going to be awfully hard to blow through any carb with a Roots type supercharger, correct?

IMHO yes, just wanted clarity.
If draw through, it can idle on 1 bbl. and synchronization isn't needed.

I remember hearing that the IDS is a better carb than the IDA for blower use. The IDS has a high speed enrichment circuit where the IDA tends to go lean at high rpm...could be death with a blower.

What is the total CFM of these carbs and what is the intended use?

Yea, I waiting for an explanation on the implied importance of carb sync in this application. maybe just an oversight?

That's the neat thing about Webers, they have a removable "choke" (venturi), allowing it to be instantly converted from a large-CFM carburetor to one of small CFM, or vice-versa. The basic carb number (48) is the throttle blade diameter in millimeters.

The internal tuning parts are going to be $$$$$

Thanks for the inputs and comments, on some forums I'm getting nothing. This setup was on a Hemi/8-71, don't know what type or size of hemi and it has been sitting for many years. I haven't started cleaning it as yet but hopefully I will find something that leads me to who built it. It looks extremely well built with linkage and gas line components like the new 4 Weber systems have. I don't know cfm but if built correctly for a hemi it should be ok for my 413 sbm which I built for a blower. The setup is going on a race car but I don't know if it will ever hit the track, if it does I'll have to find a driver. I have some experience with multicarb setups I use to run 6 carbs on my sbc in the 50s and early 60s. I believe most people have syncing problems when running these carbs on IR manifolds. In this case since the manifold and blower both are plenums I wouldn't think syncing would be as great a problem. I've certainly noticed that the individual parts are expensive and I hope I won't need many but when needed I'll just have to search until I can find something I can afford. I've always loved the looks of these systems and when this one popped up I just couldn't refuse. This setup has long stacks on the carbs so it will be like the old AFX cars with 8 tall fi stacks sticking thru the hood.

This is way above my pay grade, but isn't this blower (rotating Roots) more partial to some side to side differential airflow anyway, and likely changes that un-evenness based on the RPM?

We need pictures of this rig!

OH YEAH !

Post some pictures if you get a chance. The linkage is the critical part. If the linkage works properly so all four carbs have the same throttle position for full travel then you should be able to get it to work. Dialing in the tune might be a job for an expert.

Synchronized vs. sequential vs. progressive makes no difference.
All of the mixture is going to the same place regardless of which/how many carburetors are open how much: the extreme front of the rotors, just behind the drive gears. Very little reaches the rear 4 cylinders.

Maybe it was removed because no one knew how to jet them?

You could certainly be correct. The young man I bought them from said they were his father's and he didn't even know the last time they were used. His father sold the hemi and the buyer did not want the Webers. Who knows he was selling.

What is the intended use?? Street or drag? My un-experienced (webber wise) would be cool conversation generator at a car show/cruise nite... PIA in competition conditions.Not saying don't think out side the box but if these were worth anything but conversation starters they would be more prevalent at the track. They would look cool on an old Gasser/Nostalgia drag car that's for sure!

Next best thing to a roots hanging out your hood if you wear one!

Obviously home made and looks like a street rod setup rather than a serious race piece. If you plan on running that setup you should find someone who knows how to rebuild those carbs. It would be good to test each carb before trying to fire up a blown engine with that setup on top.

I'm sure you're right. I was looking at a couple 850 blower carbs for my engine when this came up. It was significantly cheaper than the carbs and I needed a bunch of other stuff to convert from a Bugcatcher FI to carbs. It is a race engine but I may never race it. I have another engine I'm building which will be a 360 street engine with a Procharger which is planned to go in a Notchback I am going to restore. Who knows by the time I get all this done there's no telling what will end up where. This is the car which I was planning on putting the webers on.

Look around for a local Weber guy and go from there. If you can find an old timer who knows Weber carbs he'll be able to help you get it running. I'm sure the carbs all need to come apart and be gone thru and it would be good if he had some little engine to test each one on before you try to fire up your blown engine with them. Good luck, I have no idea how to find a Weber guy except word of mouth with some foreign car guys.

IMHO a Weber expert in NA engines isn't going to be much help without blower experience.
Webers are designed to be run as IR: one bbl. feeds one intake port with almost no plenum volume separating the intake valve from the venturi. This is why the CFM of one bbl. is not 1/8 of the total displacement air flow.
I've never seen 4 X 2 Webers on a blower.
The vacuum signal from the GMC is completely unlike any NA engine. Important: a small blower, or one turning too slowly, will still have vacuum at light throttle. A large blower will have boost very quickly, so the power system (where that is in a Weber?) will come on at different RPM and throttle positions depending on how large vs. how fast it's driven.

I may have something on my site here: http://victorylibrary.com/mopar/blower/blower-carb6.htm

Yes, the signal that the Webers would get from a blower are not going to be the same as they would in an IR application. I think the Webers will work on a blower in a street rod application but I doubt they'll work well enough to go racing. A person should be able to figure it out with a few phone calls to the right folks. OP could start by calling these guys who sell a quad IDF for blowers: https://jiminglese.com/supercharger-carburetion