One of those trains of thought I tend to have when left unsupervised. It occurred to me that this is one Frank (@FishFry ) in Germany might find interesting. First: any precedent for running Bendix-Stromberg aircraft pressure carbs on cars in the immediate post-war era? The PS and PD ranges can be fitted as downdraught and might be of CFM capacities suited to car engines, which turn a lot faster than aircraft engines commonly do, or at least did. Surely more than one bright spark tried it, based on WWII experience? Presumably the instrument would have needed to be modified for automotive response requirements etc. Whether that was viable I do not know. And if there is photographic evidence I'd surely like to see it. But be that as it may: I'm more interested in the fuel-supply principle on its own. Float chambers work but I can't mentally leave stuff alone, and this has bugged me ever since I ran a Weber 28/36DCD on a daily, which would stumble in long right-hand sweepers taken at speed due to the fuel level going diagonal. I like the idea of that entire issue going away. Could a four-chamber assembly like this be adapted to a conventional carb? At it's simplest it's a vacuum-advance canister pulling a needle fuel valve. The atmospheric side of the diaphragm is connected to air-cleaner pressure; the vacuum side of the diaphragm is connected to venturi pressure (i.e. relative vacuum); the inlet to the fuel valve is connected to a pressure-controlled fuel source; and the outlet from the fuel valve is connected to a fuel sprayer bar or nozzle downstream of the throttle butterfly. This last could be a spacer arrangement as commonly used with carb-based N2O installations. All other carb ancillary systems like accelerator pumps etc. might possibly be able to remain as is. My first elaboration of this was to consider that it should work just as well on a constant-depression carb like an SU — because I'm into that polished-vacuum-bell loveliness. The system should respond just as well to a vacuum signal which varies according to a needle in a variable annular jet as to one which varies according to variable air flow through a fixed venturi. That should make for a particularly neat application, as the H and HS series' float bowls bolt on in their entirety, so the diaphragm/valve assemblies can be shaped to bolt on in their place. (SU did make downdraught carbs. Their D2, D3, and D4 types weren't all that uncommon before WWII. I was blissfully unaware of their existence until I saw four D4s on a Lagonda V12 Le Mans replica a few years ago. That put my mind to rest about the vacuum piston being able to work without help from gravity: though apparently the damper-oil filling and breather detail was different on the D types.) My second elaboration was to realise that if we're introducing a spacer with a sprayer bar or nozzle anyway, why not injectors in the relevant intake ports instead? There is no longer anything which requires the venturi and the introduction of fuel to be in the same place. Are we then on this side or on that side of the boundary between carburettors and fuel injection? Best of both worlds or a particularly wriggly can of worms? Would there be any percentage in this apart from being able to go around corners upside-down? It's Monday, isn't it? This time of year I can never be quite sure ...
Twin Stromberg NA-R6Bs. I'm not sure if those are pressure types. I'll research it when I've got a moment later.
NA-R6Bs have float chambers, it seems: (Not quite sure we're looking at the right carb here, though?)
Ned - try to find a forum specializing in pulling tractors, and pose your question there. Over the years, have had a number of inquiries from these folks. Jon
I do remember that IHRA used to make it very clear in their rule book..... NO TANK CARBS! It never mentioned aircraft though.
Stromberg offered two- barrel tank carbs during WWII that had throttle bores the same size as the secondaries in a Q-Jet (about 600 CFM measured on the 4-barrel scale or about 850 CFM measured on the two-barrel scale). A few enterprising individuals fabricated intake manifolds for these in the early 1950's. Not a lot of engines in the early 1950's could handle this much CFM, but these were banned from drag racing. This is why I laugh when I see some magazine writer that probably never saw a carburetor state the reason for tripower is there was no single carburetor large enough! Stromberg was playing with even larger versions, and I have a prototype 2 barrel that will flow more than 1200 CFM on the 2 barrel scale. Jon
Yeah, actually I do find this very interesting I really have a thing for quirky - out of the main stream stuff. Frank
I think it is an interesting idea, but; 1. The PD9 (one of the smallest two barrel Bendix pressure carbs for aircraft) has two 3-3/16" throttle bores. That is a flow area about a third bigger than all four barrels of a Holley 4500 Dominator. To me, the best fit might be one or two of the PS (single barrel) carbs. 2. If you look at the diagram, there are four or five 'rubber' diaphragms in a Bendix pressure carb that control the fuel flow. One big watchout would be finding a source for diaphragms that have the flexibility the carb designer intended. Sixty plus year old diaphragms (even 'new' old stock) might be too dried up / stiff to work. 3. You cannot call Jegs or Summit for a different set of 'jets' (orifices) if you are too rich or too lean like you can with a Holley 4150 or Carter AFB. You likely would have to make (or have made) jets to match the application.
Valid points, but my speculation was as to using the principle rather than the actual hardware, and as I mentioned, a literal vacuum advance canister off the side of a distributor — or at least the diaphragm out of one — might do the job. Of course it wouldn't be a bolt-on operation; it would probably be a process of experimentation as a sort of ongoing hobby. It would be cool if got to work.
Aircraft engines have unique demands like G loads,air pressure mixture changes and run often at constant high power loading and lower rpm compared to auto engines....Might not be all that useful on a car.... I believe principles of the Bosch mechanical injection systems of the 70's-80's can be adapted by a clever guy for a street engine...
The P-47 service ceiling is listed as 42,000 feet. So I imagine the carbs had to be tuned to adjust the mixture with the wide range of operating altitude. I even heard a story of how one poor crew chief got in trouble for tuning Jimmy Doolittle's engines to factory specs, thinking he was doing the right thing. Not knowing they had been set to run way too lean for a specific mission...
"...my speculation was as to using the principle rather than the actual hardware..." For a pressure carb I made in my basement, I am chasing two (or more) 'rabbits' at the same time; do I have the diaphragms and springs sized properly for the pressure differential(s) AND are all the jets, etc. properly sized for the application. On the other hand, if an actual Bendix pressure carb is used, it is just a matter of matching it to smaller displacement but higher rev auto engine, the basic operating issues were already solved by Bendix in the 1930s. A Bendix PD5 pressure carb has a single 2-3/16" diameter throat. They were used on the Continental E225 engine, 470 cubic inches (7.7L) 2600 rpm at take-off (maximum power). There are five or so of the PD5 carbs on Ebay at the present time. That is all I think I know.
I have one of those aircraft pressure carburetors, it's supposed to be for the engines in a B-29 Superfortress. I think it's probably a little too big for automotive use.
The story you heard may be somewhat skewed, or totally fabricated. In most carbureted piston engine planes, including the North American B-25B Mitchell's that Doolittle's Raiders flew, the mixture is adjusted by the pilot, co-pilot or flight engineer (depending on the aircraft) from controls in the cabin, not a crew chief on the ground.
I had a patient who was a B-17 and He-111 crew chief in the CAF. I know they can run on auto or manual lean/rich controls from the flight deck. He said the pilots of the He-111 were flying without a crew chief to monitor the engine settings and ran it out of gas. He wasn't on board, obviously. Of course, could have just been a war story. I was also curious how these carburetors work because they have to go through such wide barometric pressure and temperature changes that we don't encounter on automobile use. Or we'd be changing jets all the time llike in Two Lane Blacktop.
On sidecar racing motorcycles the cure was easy. Just use a float left and right of the main jet. The fuel will be low on one side but high on the other side during those long sweepers. The jet in between will have exactly the same fuellevel as when going straight. On a car carb a vented bowl could be fitted on the other side of float to compensate a little of the sloshing. Not the same but should help as well.
The similarity between the Bendix-Stromberg diaphragm system and the fuel distributor on a Bosch K-Jetronic wasn't lost on me! The problem there is that the two bowls would need to share a common needle-and-seat, centred between them. Otherwise the low-level side would admit fuel, leading to an excessively high level when things straighten out. I've spent a day or two in the past trying to get around that one! A few carb manufacturers have come up with solutions: some with U-shaped float chambers containing two floats on a common arm; others by using a central chamber under a sidedraught, like SU on the HIF series.
There are many 2 barrel and 4 barrel carburetors that fit the above description. In the 4 barrel category: Carter WCFB, Rochester 4-G, and Stromberg 4A all that central mounted fuel valves, central mounted jets, and double pontoon floats. In the 2 barrel category, common models: Carter WCD, Stromberg AA have the same configuration, just half as many barrels. Zenith also has some 2 barrels, but they are heavy duty, basically designed for low RPM engines. There are probably others. Jon
...I was also curious how these carburetors work because they have to go through such wide barometric pressure and temperature changes that we don't encounter on automobile use... If you look at the diagram in the original post, as the altitude increases (the inlet air pressure decreases) in chamber A, the fuel pressure at upstream side of the main metering (area D) jet is decreased, correcting the mixture for the change in altitude. I cannot see it in the diagram, but I assume there is a thermostatic element that makes a similar change as inlet air temperature changes.
The Jalopy Journal
