Also for my plans for a variable intake manifold, two tubes are much easier to deal with than four.  If I could have figured out a way to handle 4 tubes sliding I probably would have stayed with the four tubes.  However, for my turbo block, I decided the simplicity of using two tubes (combining primary and secondary) outweighed any disadvantage - I may prove myself wrong about that conclusion, but nothing ventured - nothing gained.

Ed Anderson

A 12A race engine with a big bridge port and very short intake runners, for best power at 9,400 RPM still makes 173.3 HP at 6,500 RPM.  SNIP

With a 13B it seems to me that this could be done with not as near as much effort as is being expended here. There is a plenum below the carb that combines the two runners. Adjusting the plenum volume changes the torque peak. I think the runner length is from the plenum to the block face.
There is little volume involved, and not much of a change is possible without shortening the runners.

So, the two into four runner idea should work fine. The effect may be even more pronounced than the four runner option.

Lynn E. Hanover 

 

Thanks for the additional insight, Lynn

 

    I intend to give it a try, but always nice to hear from someone with your experience indicate that it just might work {:>)

 

Ed Anderson