Carb inlet from plenum

[jacksoni]

I need to build what amounts to a cold air box for a long inline engine with multiple carbs. It sits low in the chassis and frame rails and then wheel wells and such are in the way so space is limited. I want to put some sort of bell mouth/ram tube/velocity stack inlet to the carb to improve air flow into the mouth of the carbs. I have seen some boxes (generally V engines) where there are ram tubes extending into the air box ( l know I need some clearance to the roof/side wall) and other situations where there is a flare built into the floor of the box that feeds the runner directly. Either way may present space issues that I have to work around. Does anyone have some thoughts about which basic arrangement (tubes extending into the box, maybe 1" off the floor vs having the flare built flush with the floor) may have an advantage or disadvantage?
Thanks for any thoughts.

[mag2555]

Are these single Venturi Carbs?
One of the main things is to set the flow up straight into the Carb by means of a straight section of air cleaner base , a length of 1.5” should be fine.

Next you need a radius leading into that straight section needs to be a minimum of a arc equal to 1/4 of the diameter of the top of the Venturi section(s) of the Carb.

So for example if the lead in to the top of the Carbs Venturi is a diameter of 1.500” then the minimum radius leading into the air cleaners bases straight section should be a arc of .750” which is a 90 degree section of a 1.500” diameter circle.
If the Carb has two Venturi’s of 1.500” then a 1.500” arc would be the way to go if possible.

[jacksoni]

They are single venturi, think Mikuni and related bike carbs. Depending on which I use, 63mm or 70mm OD at the inlet. They have been run with a K&N cone filter and it has been suggested to me that other ram tube type of inlets are of no use/help. (I can't believe that. Will be testing on flow bench tomorrow). Have attached a couple of photos to illustrate what I am asking as I am not sure Mag2555 if I totally follow your suggestion. I plan to use commercially available tubes for bikes, modified to fit.
First photo (tall venturi) shows the flare up off the floor of the box about 1" or so and the second (short venturi) down flat (more or less). I could even mount the venturi on the outside of the box which will be thin aluminum, beveled appropriately.

[mag2555]

That narrow very tight radius lip at the edge of that like the lip on a dish Is a big offender!

These pictures from one of DVs books should help you out.

[jacksoni]

Thanks. I think I can modify that lip and improve it. What about the question of down close to the bottom of the box or even incorporate that flat plane (outside the box) vs having the flare up off the bottom an inch or so s in the first picture?
I have a big radius inlet ( a "turbo inlet" ) like the DV #11 which I will test but I am not sure I can get in the space I have. May need to investigate sourcing something that really is very flat as the illustration # 11 shows.