We have seen the Offy 2 X 1 intake manifolds that mounts two standard SL6 one barrel carbs, in a way where each carb "feeds" 3 cylinders... so both carbs need to be "balanced" and working together, all the time.

What if there was a manifold that used 2 one barrel carburetors but "staged" so the engine would run off the first carburator most of the time and then the second carb. would "kick-in" when you got deep into the throttle?

Would this type of set-up give a good balance of economy and performance?

What would be the major challenges? Good fuel distribution? Progressive linkage that worked? Finding 2 good 1 bbl carbs that actually worked OK?

Is this a crazy idea or is it worth testing??
Is this one of those " it's not available because it does not work" ideas or is it something nobody ever tried?
Give me your thoughts...
DD

There are motorcycles/quads that use staged dual carburetors to good effect.
The runner configuration makes mixture variation less of an issue than might be encountered with the long differences in runner length the slant suffers.
The arrangement I have seen uses two different size carburetors on a large displacement single sporting four valves per cylinder.

It has been done, at least on a different application. Hmm. Don't know about automotive applications though.

CJ

This reminds me of the manifold adapters they had in the 1950s to put two carbs on one manifold with a progressive linkage. My personal feelings are that a progressive 2bbl would be easier and if it were large enough just as powerful as staged 1bbls. The problem is most progressive 2bbls don't have enough flow capacity. Heck, a Weber 32/36 DGV isn't enough for a 1600cc VW Rabbit with a mild cam and header. The logical (to me at least) progression is a pair of progressive 2bbls like the South African manifold or right back to the commonly seen progressive opening 4bbl. Dividing the 4bbl manifold makes for essentially a well synchronized dual progressive 2bbl installation on an asymmetrical manifold. The divided 4bbl manifold sacrifices symmetry for the simplicity of one carburetor.

So the answer is yes, this has been tried, but possibly not on a slant. Since you're essentially creating a large staged 2bbl I think you might as well run a 4bbl.

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Joshua

I would like to see a "three-pak" manifold built to run like the six-pak. Start with a stock one barrel intake, then add on one one barrel mount fore and another aft of the center carb. Tie all the runners together in a pleasing manner. Run the center carb like a stock one with a choke, but have a progressive linkage or a vacuum operated linkage for the fore and aft carbs for high RPM use.

Some good points and thoughts. My goal is to have a good MPG, reliable street set-up that has some high RPM air flow. (300 to 400 CFM range)

I have to agree that a small, vacuum secondary 4 bbl on a divided plenum 4 bbl manifold would likely give the best results as far as low RPM performance, good MPG and high RPM air flow (CFM) when needed.
I need to lay-out the divider to see how easy I can get that to work.

I have also had the "3-Pak" idea but worry about adding a lot of extra plenum volume to the manifold and the simple fact that 3 carbs are more then 3 times the trouble of a single carb. A staged 3 one barrel set-up would sure get the looks but I would not want to try to keep it in tune.
Fact is, I always got tired of keeping the Offy 2 x 1 (or ProLine) set-ups in tune... after a year or two of on-going "fuss", those set-ups come-off in favor of a single carb induction system.

I admit, the staged 1 bbl idea is still two carbs but seeing that one (primary) is doing most of the work, that is the carb to keep in good tune. The "secondary" carb. would need to be good at WOT but in theory, not as good with mid range or transitions.

I already pulled out some extra manifolds to look at and do some lay-out work... so keep the ideas coming.
DD

Doc doesn't Weber make a progressive two barrel? You know run off one venturi until ya kick it. I wonder what something like this on a Hurricane two barrel intake would fare for mpg and good general performance? Sorry Josh did read all of your post. You answered some of my questions!

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66 Lil' Red Piggie Valiant (Mater Crusher) - Thanks Zilla!!!!! 72 Demon (Number 1 Son's)

I kicked around the idea of getting two factory aluminium intakes and combining them to make a "dual port" intake for the slant. I think this would be the ultimate street intake when used with a small staged ccarb (Holley 2305, or Holley 390, or even the Edel/Carter 500 CFM carbs).

I was thinking cut the tops off both, use the top of one as the divider plane in the other, and weld the top back on. The divider plane could be smoothed and shaved thinner to take up less plenum volume, and the divider could be easily welded in place using wood spacers in the bottom of the intake which would be removed after fabrication. I would love to see one of these built and run.

I know dual-ports are disfavored amongst the racing crowd due to the loss of airflow at higher RPMs, but if you are looking for low RPM streetable power I think they are a good idea.

How about this-this intake could be made by either modifying a stock one barrel intake outboard of the carb or by fabricating an adapter that would bolt to the stock carb location where kickdown, hood clearance, and automatic choke were not issues:

Take a stock one barrel intake and add a single one barrel carb outboard of the stock carb. This could be vacuum or linkage activated, and would basically turn the two one barrel carbs into a staged two barrel carb. The inboard carb could hook up to the stock linkages, but the outboard carb would add more CFM but be positioned so that it didn't add a whole lot of plenum volume.

you could find an old slingshot intake for a flathead. you wouldn't be able to close the hood and they are very flow restricitive but it would be easy enough to rig progressive linkage up and get an idea of how it might work if properly setup.

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64' Valiant Signet 5.9, 64' Dart 170 moredoor 3.7, 67' A100 3.7, 00' Dakota SLT 4.7

As noted above, the Weber 32/36 DGV is a progressive 2 bbl but it is small for our application. I always thought that two of these carbs on a ProLine type set-up would work pretty good.

I need to keep thinking about this... I will need something better then a Super Six for the Buster engine... but it needs to be good for daily driving.
DD

You could without too much trouble try out your idea and see if it works, by scaring up a Clark Cortez intake manifold. It has the stock downdraught 1bbl mounting pad and a mounting pad for a sidedraught carburetor at the "apex" of the manifold (where the EGR valve was mounted on '73+ intakes). Originally the Cortez used a Carter YH...ptewph, no adjustability and no tunability. Better to fab up a quickie adaptor plate for a single SU or Pierburg sidedraught carb. I would think you could probably temporarily rig a hand control for the SU carb, made out of a manual choke cable. It shouldn't be too dangerous to try out as long as you were to heavily spring-load the SU throttle into the closed position (so if you let go of the hand control, the 2nd carb snaps shut right now). With this setup, all your stock 1bbl linkage would remain unmodified, and there'd be no air cleaner interference issue since the sidedraught air cleaner would hang off the end of the sidedraught carburetor. Wouldn't be too tough to find cheap carb + air cleaner, either; get one of your Canadian confreres to snag 'em off a pre-'85 base-model Volvo 240 for you.

About the only downside I can think of here is that the Cortez setup had a deflector plate bolted to the downdraught 1bbl mounting pad, which stuck down into the manifold directly in the flow path to runners 3 and 4. This was presumably to prevent 3 & 4 from getting fat at the expense of 1, 2, 5, and 6. Might want to build a slimmer wedge-shaped deflector into your carb adaptor plate.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Thanks for the reminder about the Clark Cortez intake... that would save me a lot of custom fabrication time. Now... where to find one of those manifolds...

Funny how you mentioned the hand control cable, I was thinking that a second gas peddle would also be a way to test the secondary carb., without having to engineer all the progressive linkage.
DD

What about the Japenese 2bbl progressive carbs?

Some of them were for large 4 cylinder engines (2.4-2.6), so I'd think they'd have the airflow capacity.........

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

For what it's worth, I also regularly lurk in the H.A.M.B. bulletin board. (Hot rods and customs, many of them flathead powered.) Those guys are pretty good about knowing multi-carb setups. Fairly recently, there was a thread about them, and the gist was that a two-carb should be run direct, no progression, but a triple should be run progressively.

It seems to me the biggest stumbling block will be distribution. To get "the look" right, the two singles will need to be mounted fairly centered to cylinders 2 & 5. If you're running off of the rear carb as primary, then that's going to be an awfully long distance to the front two cylinders. Conversely, using the front carb as primary.

I do like the idea of using the Cortez intake as a test mule. It shouldn't be too hard to rig a 90* elbow off the sidedraft port and use two identical down-draft carbs with small air cleaners.

Just my opinion..........Roger

Doug,there use to be a dual sidedraught adapter that would fit a standard Holley 4bbl pattern and orientate the carbs opposite of each other but feed into a common plenum.I saw one just recentley in a street rod magazine but cant remember who makes it or if it is still even in production.If you can find a single sidedraught carb that would feed a 225 ,this seems like a good setup and the carbs could be installed fore and aft,or side to side and hood clearance shouldnt be a problem.
I will check through my old magazines and see if I can find any info.

HyperValiant

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1960 Hyper-Pac Valiant(rolling test-bed)
1963 Valiant V2OO(Son's summer project,- he just turned 15 )
1972 Valiant 4dr(Daughter Kelly's repair in progress)
1974 Valiant (v8) daughter Kelly's work in progress

that's an Offy adaptor, which is still available I think...

-D.Idiot