Projects Modifying SBC 1x2 manifold into 3x2

I'm looking at adding 2 Rochesters.
Despite heaps of searching I cannot find any one else that has attempted/done this, all home-made 3x2 seem to be sheetmetal.
Due to being in New Zealand, second hand manifold never come up for sale, and anything out of the USA plus shipping-then coverted to NZ dollars is looking at over $500.
Carb center spacing will be the same as factory.
I'm planning to drill into the manifold, weld carb mounts at the green area, get the 3 faces machined.
Then run a progressive linkage.
Has anyone done this? Any thoughts or ideas?
Thanks Aaron.


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I have not done it, but had a chance to buy one years ago. It looked like he sectioned 3 manifolds and brazed it together. Well done. I regret not buying it.

 

Oh yes, I was more thinking opening up the mainfold, then shaping the bottom of the spacers like this to fit.


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I know they make Aluminum spacers, are cast or steel adapters available?
I also like thinking out of the box. I understand this a lot diff. than what you are trying to do but it does show that anything is possible.
Took a Creitz SBC Aluminum single 4 manifold, cut top, made an Aluminum plate for 3 Deuces and progressive linkage................................

 

If I can't buy a steel unit of the shelf, I can make a couple, then I can make them thick enough to mill back down to match the center carb hight.
Cheers Aaron.

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If making steel spacers from scratch I would make the outside perimeter rectangle instead of all the curves..............................

 

Seems feasible to me, I say give it a go

 

I don't have a cast 2 barrel manifold in front of me at the moment BUT looking at your top pic it looks like the bottom of your spacers will have to be contoured so as not to restrict the dual plane floor of those higher runners trying to reach the lower runners...........................................

 

Yes, I plan to drill the new inlet holes, then shape the bottom of the carb mounts to suit the profile of the manifold. I'll mark the position of the mounts, then measure from the lowest point of where it will touch, to the top of the center carb mount plus a little bit for milling.

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Hi Brigrat.
After rereading this, i was only thinking of the out side edge that will be seam welded.
Where I drill into, will end up joining the two planes together. So I may have to remove all the internal divider between the two planes, from the center carb to maybe an inch befor the port face???

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Yeah, that's what i think too.
I'm sure someone will chime in that has done this already, HotRoding in the garage at its finest, untill then I'll just get into it.
Cheers Aaron.

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Seems like a lot of work to save $500, but an interesting project, and that is what hot rodding is all about.
Watching with interest !

 

I haven't examined a 2 plane manifold closely, but it looks like you would have to scrap the 2 plane layout more or less completely to have multiple carbs on it. Making a hole and adding the extra carbs where you marked would only connect them to the upper plane, making half the engine draw air from one barrel of the original carb and all of the new ones, while the other half of the engine only draws air through the other barrel of the original carb. Obviously a waste of time, you need to open up so all cylinders get the same "amount of carburetor" - and that probably means killing the 2-plane design, letting all six barrels feed all 8 cylinders.

 

Keep us posted on how you make out with your idea. I'm sure a lot of guys would be interested to see how you do. I know I am.

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It takes a lot of over time at work to end up with $500 extra cash in hand!
If I can build the manifold myself, I can use cash for carburettors, carb rebuild kits and linkages.
I will keep track of hours spent on this, and keep you all posted.
Cheers Aaron.

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Correct, I won't know till I get into it but it may need a hole almost as large as the green rectangle, and deep enough to join both planes together. Then taper the block I'm welding in, so its 'port matched' to the new hole. And smooth everything in there so airflow is not terrible.
Thanks Aaron.


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Back in the flathead days, there was a company that offered risers to do this to regular Ford cast iron manifolds (Gotha? Almquist, Eelco?). The way the runners were arranged on a flathead, it probably worked OK. I can see that there would be a problem with the Chevrolet dual plane thing that would probably be solved with a lot of work, cutting and shaping).

 

Check out Vintage Speed websight. They sell an adapter to mount 2 Rochesters on a stock manifold. Have one on my nailhead. Run a primary and a secondary carb with progressive linkage. Works great and looks vintage.

 

Yeah I’d thought about the intake design as well. May want to look into how to tune individual runner intakes IR , this isn’t neccisarly that but the threads tend to have lots of good info on how to tune various intake designs.

With 2 carbs feeding one half, the middle feeding thenither half or some other weird combination I think a lot of the running gets easier just running them all direct with no progressive linkage. Just keep you foot out of it bumming around and I bet the mpg isn’t all that different

 

Thanks, Vintage Speed have some really nice stuff. I considered this

For my current 4 barrel manifold that I have on my car, but with my old 2 barrel manifold sitting round doing nothing-I started thinking, 3x2...

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I can't tap into the lower plane as the upper plane is in the way, it looks like it will be a take on a single plane.
Cheers Aaron.

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So discussing this with my Dad (a mechanic) he said his usual line of
'Chevrolet spent millions on developing that'
He pointed out joining the 2 planes is going to be a terrible and tricky job! And the 3,4,5 and 6 cylinders may run richer.
We came up with this option, raising all 3 carbs high enough to allow a 'C' shape port to enter the lower plane on the out side carbs.


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This is all way to over my head, goodbye & good luck!

 

Thanks, hopefully it ends up as nice as your Creitz.
Cheers Aaron.

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I don't know how available they are where you are. But you might find some of the later Throttle body intakes would work better.

 

39 aaron we just got in one of the aluminum throttle body chevy intakes at work. I could look into shipping cost to send it to you if you'd like. No charge for the manifold.

 

Just my two cents; the Creitz is a single plane manifold and if you want something to work similar look for a cheap used Offenhouser single plane four barrel intake manifold, mill the top off and weld in/on your own with your desired 3x2 configuration in it. Aluminum is also easier to work and weld on than iron.

 

My son's pal (machinists) used one of the 'centerfire' Chev fuel injection manifolds, Blanchard ground a 1/2" plate of aluminum to fit, then machined it to fit four 28/32 Weber 2 bbl carbs, 'staggered'. ('Man-a-Fre style')
The carbs are found on Pintos, early BMWs, etc. Very plentiful, each is a progressive 2-bbl.
So...straight linkage for the easily-intimidated. (Four 28 mm primary pairs can be economical.)

 

39 Aaron, not sure what sort of small block you're working with but if you had some 96 up vortec heads you could use this lower intake used on vans and the Denali to make a number of different setups.

 

Hi Joe, that's is a nice offer. Is that a TIP intake?
Dose it fit old sbc heads like I have? Or the Vortex heads?
Are you in New Zealand?
Cheers Aaron.

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