I am thinking of making an intake manifold for attaching a single 50mm DCOE weber. It would simply replace the two SU's.

I am just at the concept stage and about to buy the 50DCOE....any suggestions/input on how to optimize the design or (been there done that) is most welcome.

I do not think it will have any performance benefits but it should be more tuneable.

Very cool idea. How will you adapt the manifold? Will you start with an SU manifold and start TIG'ing? Should be a fun build. Looking forward to following your progress.

If there is no performance benefit, how would increased tuneability help? And given that you can modify the SU needles and use an assortment of jets and damper springs to tune SUs any way you want, I argue that the difference in tunability is much less then you think.

Air flow will be about the same through the carbs orifices so not much of a difference there for power.

The Weber has 3 circuits where as the SU has one so air/fuel can be tweaked more conveniently on the webers for different conditions however I take the point that needles are infinitely tuneable.

For the manifold, having 3 runners and optimizing the same distance and curve impediments into each carb throat will be the challenge... sort of like building an exhaust header. Maybe a plenum like on an EFI intake as an intermediate buffer would also work.

Still building up ideas so thanks for the quick input

Edited December 29, 201212 yr by Blue

For the manifold, having 3 runners and optimizing the same distance and curve impediments into each carb throat will be the challenge... sort of like building an exhaust header. Maybe a plenum like on an EFI intake as an intermediate buffer would also work.

This is already an issue on the stock manifolds for SUs. It has always seemed to me that #2 and #5 don't get as much mixture. If you can't improve the manifold distribution, I don't know that it'd be worth the effort.

As for the 1 vs. 3 tuning circuits, I'm with John. The "single" circuit of the SU is infinitely variable throughout its range. It does take a bit of study working through the interrelations between needles, nozzles, damper springs and oil choices, but with some effort you should be able to duplicate anything you could get from the DCOE.

And if more performance isn't the goal, then the baseline 4-screw SUs from the '70-71 240Z give you a really good base tune anyway. Is "more" tunability really needed? A set of roundtop SUs on the later flattop manifolds look like a really good all-purpose street setup to me.

Hang that 50 in front of an stock efi manifold at the throttle body, facing forward. No one's done that yet! (have they?). Would that dizzy in the way? Heck, would the rad be in the way!! Gotta mock that up.

Big on cool factor, not sure you'll make any real difference performance wise like the opinions above. Do it anyway!

Edited December 29, 201212 yr by zKars

If you would like my advice, I would do a few things. First, I would come straight out with 6 intake runners that are exactly the same length, say 4 inches. Make all of those runners go from a one size at the head say X mm, an open up conically a bit to say X+0.25in. THen I would attach all of them to a large plenum (like an EFI manifold). Then most importantly, I would have the plenum heated to keep the fuel from every being able to pool. This is the greatest challenge for sure. You have to make sure all 6 cylinders get an even distribution fuel, and not have lean 1 and 6 and rich 3 and 4. The plenum may have to have some directional channels inside to help out with getting the fuel to all the cylinders at the same velocity with the same amount of entrained fuel.

Hang that 50 in front of an stock efi manifold at the throttle body, facing forward. No one's done that yet! (have they?). Would that dizzy in the way? Heck, would the rad be in the way!! Gotta mock that up.

Big on cool factor, not sure you'll make any real difference performance wise like the opinions above. Do it anyway!

You can eliminate the distributor with EDIS or other such crank fired method. I agree with Steve though, biggest problems will be uneven distribution and pooling.

Thanks guys,

I gave the balancing some thought and a method for addressing. Here is the idea:

Test bench flowing of air into the manifold at the carb mount and measuring the flow out at each runner could possibly simulate the manifold in use. Some extended dividers/vanes inside the manifold at a point between the 3 converging runners may enable some tuning of the flow between adjacent runners. However this would be for the 3 runners being side-by-side.

With further thought: converging 3 runner tubes at the single carb throat must have symmetry rather than being side by side as in the stock manifold to balance better. An analogy would be like the collector where the exhaust runners converge on a single pipe. Next step is to ensure the 3 runners' impedance is similar.

I did a bit of web searching and found others seem to point away from a significantly sized plenum.

Edited December 30, 201212 yr by Blue