I agree on your intake it sounds like you can't run progressive since each carb is fueling 2 runners. You will just have to jet down and see what you have. It'll work. Keep the air flow unrestricted! I don't think they can have too much air.
Yeah, they can. When there are too many venturi, or they are individually too large, or both, there will be insufficient air velocity through each to properly draw fuel into the engine. This will kill off idle and low speed operation. "Jetting down" a carburetor just makes it leaner, not smaller. If the air velocity through the venturi is already too slow to properly meter fuel, that lean condition will be exacerbated by reducing jet size. That's a recipe for burning metal things.
Have you actually looked closely at the intake to be sure its designed for each carb to only fuel two cylinders, or just assumed it was that way ? Not trying to be negative, just asking to be sure that its designed that way. I'd like to see a picture of the bottom of the intake manifold. Just wondering if it might be possible to modify it in someway to gain commonality between the cylinders. Also wondering if it has any sort of plenum?
It’s a Weiand intake,,,,I’m pretty sure the center carbs will feed all the cylinders . It’s a good idea to double check though. Tommy
While the center carbs might feed all the cylinders (assuming it's an open plenum design), you might find that the outer cylinders run lean while the inners are running fat. If I were to set that up with progressive linkage, I might run it like a dual quad setup with the first and third carbs acting as the primary carbs and the second and fourth as the secondary carbs. That doesn't change the fact that, as others have mentioned, those four carbs are probably too big for your engine and the inlet venturi size might be too large to tune. On a blown motor, this can be overcome but in a naturally aspirated engine, one is relying on the vacuum created by the pistons and atmospheric pressure (14.7 lbs) to draw the charge into the cylinder. The larger the venturi, the more vacuum required to draw in the charge. Now, to answer your question, I would run 3/8" hard line from the tank to the fuel block, with a regulator on the end. Ideally, a return would be incorporated after the regulator, but that gets a bit "clunky". From the block to each carb, 5/16" hose would suffice. Adjust the floats to suit, sync the carbs, and you should be a happy camper with a neat engine!
Maybe this will help with the velocity question: This is part of what one learns in the Carter Carburetor Company factory school. The image shows several glasses of water open to the atmosphere, with tubing connected to various areas in a multiple venturi. The water head in the tubing shows the differences in signal, based on venturi air velocity. Jon.
I agree with what you are saying. Most intake manifolds suffer from that malady as well. Its kind of a matter of how much the individual design makes the engine suffer. There appears to be a common plenum so that the intake passages are not operating totally independently. I don't think its a good design no matter what carburetors are used, but I think the carbs in question are large enough to be problematic. I would see if the carbs could be sleeved to make them smaller. Adding higher compression aluminum heads and a high performance ignition may also help burn excess fuel variations.
Look at it this way: the 426 Hemi and 427 Ford, both with 2 x 4bbl carbs, and 7000 rpm capability, were factory equipped with 3/8” fuel lines. Most other cars, including the 383, etc, were 5/16” lines, and probably a lot longer than a pre war Ford flathead that may, on a good day, put out 200 hp at 5000 rpm. 5/16” line should be easier to bend and route.
As others have mentioned in this thread, you need to inspect that intake manifold with it off the engine and the carbs off to determine if the carbs are interconnected or the manifold is a true IR manifold. If the carbs are interconnected, you probably have too much carb, but you probably are not going to be able to block off two of the carbs OR run progressive linkage. If the carbs are NOT interconnected, the carbs may actually be too small. The manifold design is important. Jon
It is SUPER important. If it has an internal balance tube, I honestly cannot see how it can be made to work properly on a road-going engine, except maybe with 81's.
Using some quick cocktail napkin math, your Flathead needs around 312cfm at power peak. That's at 100% efficiency with a 239ci engine making max power at an engine speed of 4500rpm. Assuming your engine is more likely around 70% efficiency, you're looking at a cfm requirement around 249. Given that, you can see why it's not possible to simply "jet down" to get that 2x4 setup to run correctly without cutting off some of the incoming air (IE running only two carbs, progressive linkage, etc). It does look cool though!
If there is a balance tube, and there's a plenum under each carburetor, maybe he could put a screw in instead of the jet in one barrel of each carburetor and block the barrel. That would cut the cubic foot per minute rate in half, and it would be a whole lot closer to what the engine needs. Still too much, but a whole lot closer.
Another possibility might be to limit the travel of the throttle (not allowing WOT) and install larger jets in both the main and idle circuits. Carburetion 101 - there are 3 major ways of improving atomization: (1) increase venturi air velocity, (2) increase heat, (3) increase the fuel supply. Maybe (3) would balance the problem with (1). Jon.
Check Valve is the wrong name [my apologies] , It is an inline pressure relief valve. On our old touring car we used one made by fuelsafe [but it wasn't cheap] We used a Bosch EFI fuel pump and held the pressure at about 30 psi to prevent vapour lock. Then we Tee'd off a deadhead Holley regulator to a 600 Holley carb. This was in a class with a controlled Carb, and the sanctioning body required pump gas [so vapor lock was a problem with our 98 octane ethanol blends] A single fuel line to a deadhead regulator would cause fuel pump failures ,whereas the Bosch would run forever with a return line. Gear type fuel pumps really benefit from a return line You could probably use a holley bypass regulator near the fuel tank [block off the carb port, and Tee of any carb fuel lines]
I may be wrong about this, but 5/16" line equates to 5AN . If someone plumbs a system with AN type fittings, I don't think they are available or are extremely difficult to find. JIC fittings can be found though. While working on an off topic higher pressure fuel system, I needed 3/8 line for the pressure side, but the return had to be a 5/16 line. That was because the fuel pump had a plastic connector that was 5/16. I could not find any AN stuff in 5/16. I ended up sweating/soldering a 5/16 tube inside a 3/8 to get the size I needed. Someone could use brass fittings to work it out, but I just don't think 5AN fittings are available. Someone correct me if they know a source.
Looks like it has a passage from the centers to the end runners,,,,,,you can also use a light and see in there too . Like the other guys have said,,,,,those Strombergs only want 2-2.5 pounds pressure. They are very sensitive to excessive pressure,,,,run like crap with too much pressure . And,,,you can do what you choose,,,,,but I don’t think it needs AN fittings and braided steel lines,,,,,,too over the top for your application . Some nice 5/16 lines and normal clamps will be great,,,,,and a normal regulator,,,,,,,don’t make it too high tech,,,,it doesn’t need it . Tommy
I believe Desoto29Hemi is correct that the center passages connect to the end passages. That said, the passages look small and inefficient compared to the actual intake downward passages. My suggestion would be to mount the intake upside down in a milling machine and cut those passages completely out, maybe on down a little more into the vertical tubes. Then make an aluminum plate to fit in the bottom and have it Tig welded in place. It would create a plenum. You could even divide the plenum front/rear if desired. Creating a plenum would allow easier balancing and somewhat better fuel balance. You could even make a dummy carb or two and still get resonable balance. It should be no worse than a 4 barrel sitting on an intake. Those little passages between the vertical tubes look like a torturous path for any fuel to follow and a good place for puddles of fuel to collect and make tuning a nightmare.
If you have to run all 4 then use Stromberg 81' off V8 60's. If you don't have to run all 4 carbs, Block off the 2 end carbs, you don't need 4 carbs, 97's want about 3 1/2 pounds of fuel pressure so you'll need a fuel pressure regulator and one of the 2 center carb with a choke.
While you are at it you may want to make a provision for a PCV in that intake. I had to retro fit one on a finished, running engine to eliminate drips and odors (from the flathead ). Easier to do it now.