Changing from updraft to downdraft carb?

I have one of those cars that used the Stromberg UU2 carb that seems to be very scarce. Not only are they scarce but any I have found are badly cracked and not good cores. I was wondering if anyone has experimented with changing the intake manifold to a downdraft by manufacturing a replacement manifold? I also have a manifold that has cracked in numerous places so it would be no great loss to improve the manifold if possible. The car is an eight cylinder 31 Hupp model L and I haven't been able to find good manifolds either intake nor exhaust.

Well, Hupp probably build eight cylinder engines with a downdraft carburetor. So a intake manifold off one these engines would be the easiest way to use a downdraft carburetor. A intake manifold can be build using tubing. The biggest problem would be making the plate that goes against the block and the carburetor mount. Another way to go would be to replace the Stromberg UU2 carburetor with a Carter BB-1 updraft carburetor. Carter sold lots these carburetors as replacements back in the day.

Yes Hupp built later 8 cylinder models with downdraft carbs and possibly by checking the gasket configurations I might be able to find a match. Even if I did find a match those engines and parts are very scarce as well. I have had a Carter BB-1 carb on my 29 Hupp 6 cylinder as a replacement and that is an excellent carb. My concern is that the Hupp 8 manifold was specifically designed to feed four cylinders from each of the two barrels of the carb as in the Stromberg UU2. Not being a carb guy and not knowing what complications might arise is my main concern so as to not over or under fuel the motor and possibly do damage of some sort.

I have a 1928 Dictator which some previous owner switched from an updraft (UX2) to a down draft carburetor. Your application would be different because yours is an eight not a six. My car now has a Ball and Ball E7T2 carburetor. The change was made by cutting the connection between the intake and exhaust manifold and turning the intake manifold over (180 degrees) with an extension added to mount the carb on.

The only difficulty I have experienced was a lousy weld on the exhaust manifold to fill the hole where the it used to attach to the intake. I had this professionally rewelded to fix an exhaust leak I couldn't seem to get just right.

I think the car has more power than it would have had with the original updraft carb. I could take pictures and post them of the setup if that would help.

My records show several different sized Hupp engines using the Stromberg UU-2 carb, and all of these differ from the later Hupps using downdraft carburetors.

As I have posted previously, when doing a carburetor migration, FOR BEST RESULTS, the "donee" engine should be within plus or minus three percent of the "donor" engine.

Unless you are hung up on "period correctness", a modern carb from a '50's or '60's pickup with a similar sized engine should function well, and would have a manual choke.

Jon.

Thank you both studeboy and carbking. At this point the turning over the manifold seems like a pretty good idea from the standpoint of the diameters/volume of fuel mix and air flow being the same as designed.I was thinking of having a new manifold made but was concerned as to the importance of design and sizing. As for "period correctness" I am willing to sacrifice that for a trouble free non malfunctioning carb of more modern heritage. Jon are you suggesting that the cu. inches of the donor engine should be plus or minus 3% of the Hupp engine in order to function properly? This 31 Hupp eight was rated at 90 horsepower @ 3200 rpm with 240.2 cu. in displacement compression ratio 5.2 to 1 . I sure would love to avoid buying the wrong carb if at all possible. One other concern is trying in some way to duplicate the fuel air mix as per the original design of each barrel feeds 4 cylinders.

According to the factory Stromberg records; the 1930 Hupmobile with the 240 CID engine used a Stromberg UU-2 during early production, that was replaced mid-1930 with a Stromberg UUR-2. The same UUR-2 was carried over into the 1931 models.

The UUR-2 (the "R" meant revised) has a cast iron throttle body, and the bowl assembly is of a different mix zinc alloy than the UU-2. There are restorable UUR-2's available; I will not say they are inexpensive.

The Stromberg part number for the UUR-2 is A-15304; the Hupp part number is 78990.

Since information is available on the UUR-2; should you decide to build a different manifold, do your homework, and determine what more modern downdraft two-barrel would have the same main venturi size as the original UUR-2.

Jon.

Here are the images you requested Bill.

My thoughts on this conversion is what downdraft carb are you going to use? for that period, a stromberg EE-22, EE-3 are probably correct. and those carbs are not cheap..

Why not shop around and see if you can't find a good UUR-2 ?

GLong

I agree with Greg, for what it's going to cost to convert, you can get it set up they way it was new.

A few photos of the Hupp engine with manifolds would help.

I've seen a two-barrel-to-single adapter used on an 8 cylinder duplex manifold, I don't know how the car ran, but it did run.

Is your UU2 completely junk? or is is missing ?

GLong

The original carb is gone. I do have a picture of it though. I have a replacement UU2 but the pot metal has been expoxied and really is only a spare parts carb. I fitted the manifolds today and there is no way the intake can be flipped over due to bolt hole configuration. Now I'm back to sticking with the original manifold set up.

That Carter bb-1 was some sweet piece,,,good mixture over wide range

Leave it as a updraft,,,,At least it'll look right,,,

Cheers,,Ben

I would find a nice BB1 so you can make a quick adapter and get her running. You can take your time finding the correct carb. Have BB1's on 3 cars, all updrafts all start and run great. You can even sell the BB1 when you get the correct carb.

The problem for the OP in trying to use a Carter BB-1 is that his original UU-2 is a TWO-BARREL! The Carter BB-1 is a single-barrel.

Jon.

Yes, but a siamese adapter using the single barrel, feeding the 2bbl manifold will work, I've seen them, made the adapters etc.. Not a 'correct' operation, but at least the car is rolling down the road.

Then with persistance and some luck, a 2bbl updraft may show up.

GLong

We have had a number of customers try to use the "one into two" adapters, totally given up because of less than optimal performance (even assuming room to mount the adapter and carb); and looked at other options.

A much better option that the one into two is to fabricate a new manifold for either a larger single barrel carb or for two single barrel each the same size as one side of the two barrel. We have had a number of customers report back that the dual setup worked better than the original on the straight eights (better cylinder fill ratios on the end cylinders, and more contant A/F ratios on all cylinders).

Fabricating an intake is not difficult if you can weld aluminum (I cannot, but I know welders that can).

One can acquire a piece of aluminum "sheet metal" with a thickness of one inch (3/4 might work as well) for the piece that bolts to the cylinder head.

Preformed bends in 15, 30, 45, and 90 degree angles of the correct diameter may easily be acquired from an electrical supply house (its called conduit).

The flange can be part of one of the adapters.

Make sure the plenum is as large as the original plenum.

Jon.