Okay, so my memory banks are dying (old age). It seems to me that years ago (lotsa years) in our club we had a guy who ran a three carb intake on his flathead. The only carb that was "alive" was the center carb. The front and rear carbs were dummys. Blocked off with solid mounting gaskets (aluminum plates). Linkage was direct between all three. Fuel lines were plugged, but ran to all three carbs. Someone just mentioned that they don't think this can work since each carb was dedicated to certain cylinders. The manifold was an Offenhauser. It sure looked sweet. Am I suffering from false memory? I need to know or It's off to the home. And, MERRY CHRISTMAS!!! Bill [email protected]
Hey Slam, thanks. Over the years I have done so much, heard so much, seen so much...I have trouble sometimes sorting what really happened. Where did all those years go? DAMN!!
I have seen that done many times myself too ! You are correct in your thinking . As long as the center carb is used that way you are fine . That's no different than a single carb setup that came with the car ! They sell those block off plates on ebay ! I saw them under " ford 312 or ford 292 " Can't remember but it was this past Monday !
"I have trouble sometimes sorting what really happened. " Yeah I know how it is I have the same issue from drinking
I sure hope that's the way it works; that's how I'm planning to run three singles on my Plymouth flathead 6.
I have a double manifold and would like to know which carb is better to run the front or the rear. I am serious as it was raised as a could be issue by starving one end of the block???
I dont think it matters because the whole Intake manifold is just a chamber itself for the fuel to turn to vapor untill the intake valve opens to the cylinder and thats when the fuel is used. should always be enough vapor inside the intake manifold to keap it going, may have to fuss and fight with the mixtures on your carb though.
I would use the carb that is closest to the center of the engine . That way the gas spray is equal front to back or close . If side by side I don't think it will matter .
you want to get the best fuel distribution. if you mount only one carb on a duel carb intake it might not be the best way to go. have any pics of the set up?
No pic's as it is not set up yet but it is a Burrell manifold used on the flathead Cadillac engine which runs two rochester 2 barrel (2G) carb's.
I used to have three 2s where only the center carb worked under normal conditions, but when you tromped it the 2 end carbs lit up. JB
How about pics of the manifold? I'd like to see how close or far apart the carbs will be. Even though both carbs share a common plenium, the front cylinders will probably run leaner than the rear cylinders if you use the rear carb. I know dual quads on a bbc will make a 15 degree difference in coolant temp depending on if the linkage is progressive or one to one. On sbc, the difference seems minor.
One has to look at the plenum area and interconnections in the manifold; as well as the runner configuration. Most 3x2 manifolds (8 cylinder) are set up such that the single center will work (albeit less efficiently than a single 2-bbl on a single 2-bbl manifold). A few manifolds cannot be used in this fashion. On dual manifolds used on the street (MOO), better to use a pair of smaller carburetors and run both simultaneously than to run one only. The same is true with 3x1 on a 6-cylinder. Three somewhat smaller carbs all working simultaneously will give much more consistant mixture to all cylinders, thus increasing efficiency. Not familiar with the Burrell, but have set up numerous Detroit Racing 2x2 on the older Cadillac engines running both 2 barrels simultaneously. Jon.
Just run them both. I ran 2 97's on a worn out completely stock Merc with absolutely no problems. Each will distribute the correct mixture (if it's adjusted correctly) but only 1/2 of the mixture that the engine is calling for. The other 1/2 comes from the other carb. Where the carb is mounted makes no difference as long as there are no vacuum leaks. (within reason!) The air/fuel ratio is determined by the carb, inside that carb, before the mixture passes over the butterflies into the intake. Once it enters the intake it won't lean out unless there is a vacuum leak to change that ratio before it gets to the far cylinder. If it did then the 4 corner cylinders would be lean from a 2 bbl carb in the center of a V8 intake and the center 4 would be rich and we all know that that doesn't happen.
Where the carb is mounted makes no difference as long as there are no vacuum leaks. (within reason!) The air/fuel ratio is determined by the carb, inside that carb, before the mixture passes over the butterflies into the intake. Once it enters the intake it won't lean out unless there is a vacuum leak to change that ratio before it gets to the far cylinder. If it did then the 4 corner cylinders would be lean from a 2 bbl carb in the center of a V8 intake and the center 4 would be rich and we all know that that doesn't happen.[/QUOTE] You nailed it Tommy. That's the same example I have been using for years trying to explain to guys about 1 little carbies running all 8. Oh, by the way, for anyone that wants to run "dummys" I have the stainless block off plates in the 3 bolt pattern available in the FOR SALE section.
You are correct. Blocking the two end ones and running on the center is done a lot. Probably more people have them like that than the real thing. I spend a lot of time convincing people that mine is running on all three. I have it that way simply because of my aversion to 'most anything that isn't functional. Of course, your memory is right on, it will run on the middle one with the other two blocked because with progressive linkage it would be only running on the middle one up to 1/3 power anyhow. Go for it, it looks good and tuning is easier.
I would not try to run just one carb on a two carb manifold. It just won't distribute well. It may work ok, but I wouldn't do it. Just run the two carbs. Even if the tuning isn't perfectly balanced, it'll be better than running just one. The simple fact that you have two carbs isn't going to wreck your gas milage. It's how you use them. If you have it tuned to run fairly lean, it will be fine on the street.
The biggest reason that people block off the end cars on progressive 3-2 systems is that they are unfamiliar with or unwilling to make the modifications that are necessary to make the end carbs function correctly. 35 years ago I blocked off the end carbs too. It wouldn't run with all 3 hooked up. It ran so well with the ends blocked off that I never got around to fixing them correctly. I was lazy. This time around, I did some research and made the modifications to make them work as desired. The engine is new and I'll block off the end carbs while I break in the cam just in case. Once the engine is broken in then I'll deal with dialing in the trips. I don't anticipate any problems but I want to break in the engine without any complications.
Where the carb is mounted makes no difference as long as there are no vacuum leaks. Not true. The internal manifold volume between the intake port and the carburetor venturi damps and buffers the vacuum signal. More volume = weaker signal, leaner mixture. Mix leaving the carb is not always as vaporized as we want, either, and droplets tend to flow to the closest runner.
I tried it. With two carbs, if you block one, you loose efficiency, using the test model I came up with. I have two Rochester pot-bellies on my 250 Chevy motor on Offenhauser intake manifold. Out of the blue, somebody said that my gas mileage would suffer with two instead of one. Since I don't give a shit that much gas mileage I blew it off. Then he nagged me about it again. So, I got curious. I did a couple of test runs over a week or two, mostly IH speeds and got a feeling for what mileage I was getting with the carburetor-twice, because up till the OP brought up gas mileage I didn't care. I never have made it a habit to check mileage. Then I put a plate in between one of the mount flanges and the carb. Cranked it up, adjusted idle and repeated the test model I had followed when checking the two.. I don't know about other manifolds, but with the Offy it ran fine, didn't notice any diff in performance, but I got one mpg better with the two, than with the one.
Tommy , I agree with you about the 3x2 and break in . You don't want to over rev a new rebuild at all . Another reason on the block off of the 3x2 outer carbs is that when you deside to mash it to the floor , the gas gauge won't be moving to "E" as fast either !! It really isn't that hard to get the outer carbs to work well . First block off the mixture settings and take off the chokes to start with and go from there . There are places that can set them up for you or you can get the information off the internet now . Just think about the racers that use all 3 at the same time !
I kinda take exception to some of the postings here. There is an implication that those who don't "run 'em all" are incapable of tuning them. Hmm, I guess my experience with Lucas sliding throttle injection on a McLaren Mk. VII Can-Am car doesn't qualify me to set up and tune Strombergs. And forget my years in USRRC with a Chev powered Cooper Monaco....Webers. Sorry, guys, it is not always lack of skill that prompts one to block carbs on three or more manifolds. Sometimes it just for show. That, plus, having a flathead or two, neither of which has been modified in any way other than heads, headers and a three carb intake. So, to those of you who knock the idea. sorry, but we can't all be so perfect. I wonder if there is ANYTHING on your car that might not be totally functional? Like maybe just for show? Maybe "chrome"? Sorry to rant a bit here, but after all these years I feel I have defend us "lazy" types. And, even though I have been a target for my thought regarding blanking carbs...... Have a MERRY CHRISTMAS!! (smiling all the time I have been typing)
Seems like you shouldn't have any probs setting up a fake intake system considering your background. And perhaps I shouldn't question the motives for doing so, but it seems that sometimes more effort is put into something fake than if it was setup as designed. Why not set up a pair of carbs and run them on the ends with the middle carb blocked off with a plate and no carb installed there? Lots of stock and mild engined flatheads have done this and it works well. Everything on my 32 roadster and the project 31 has a reason for being and no fake stuff whatsoever. Some chrome, but it's known as a potective finish as well as being good looking....
Interesting experiment with the mileage gain. I've read that before and what may be happening is better fuel/air distribution is what improves mileage. Most people seem to think that two carbs are going to use twice the gas. If your engine pulls so much CFM, airflow through the double carbs at full or partial throttle is halved as compared to a single carb and only half the fuel will be drawn through the metering systems of each carb in a double carb system.
Never understood the need for: Multi carburation with blocked off carbs. Spotlights that don't light up. Lake pipes that don't dump engine exhaust. Still don't understand the need for Oldsmobile valve covers on small block Chevys. Gauges in dashboards that don't work. Why people try to age paint into looking like patina.
Yes, I agree. Your description, (better fuel/air distribution) means to me, that even though MP and Mixture would be constant, with one blocked off, the abstract differences in distances during scavenging (at valve overlap) the inertia of the air mass at the fatherest cylinder/s would suffer slightly, compared to that at the nearest cylinder/s. In that L6 the difference is huge with a carb off center. Ha. Are we saying that one could remedy that by adding (itty-bitty) lump ports at the contributing 2 cylinders?
Got me there with the lump ports. Maybe. Single (4bbl) intakes on V8's can contribute to different mixes to each cylinder. The carb on my 462" Buick engine sits to the rear on both a stock 68 factory intake and an Edelbrock Performer. The front two cylinders run a touch leaner as noted by the slightly different shade of tan on the plugs. A bit better with the straight linkage dual quads on plug color. I've always thought the 38-41 (think those are the right years) Buick straight eights had dual carbs more for better fuel/air mixture qualities in the long runners than it did for power. They did their bit for horsepower as well. Didn't hurt that the public then perceived the Buicks as extra powerful with dual carbs. Then there were the five 97's intake on the straight 8's that were pretty breathtaking in appearance and if the engines were built up in other areas - cam, dual exhaust etc. - they made for good street runners in the long nosed Century coupes. I don't know when fake stuff came in, but I don't ever remember seeing it in my town - cept maybe for the time I had to run 8" drag slicks on my stock Plymouth simply to get to next payday and new tires. Most interesting when the rains came. The best one I saw, best for easy to detect, was a nice 40 Ford coupe in Central California. SBC, 471 blower, one 3/8" wide V-belt that drove water pump, alternator and blower. The owners explanation was that they were only pumping 5# boost and the V-belt handled it all ok. Geez, one 3/8" V-belt slips on my Buick engine when you romp the throttle, it musta really slipped when at "full boost" on the 40. Nuff for now, it's up to 24* F, gotta fire up the roadster and go to the donut run....
The Jalopy Journal
