DIY carbureted intake design plenum size

I was doing a mental build and found these pictures which gave me ideas.

My first thought was to do runners like this with a plenum higher up connecting the runners.

But then I saw this and wondered why not do a top plate to make a larger trapezoid plenum with no runners?  

I can think of the pooling issues but what would the larger plenum do performance wise?

Lose velocity and atomization.

You want runners, sized to match your ports, and tuned to length for your desired rpm range. 

In reply to Pete Gossett :

How do you tune to length?

There are formulas and likely on-line calculators that will help you out.

"Some say" that the intake runner volume (from plenum right up to the back of the valve) should equal the volume of the cylinder, and that the volume of the plenum should equal the displacement of the engine.  All we know is: it's gotta look awesome.

The general rule is short runners are good for high RPM and long runners are good for low-end grunt. Lots of engines actually have variable length runners for a nice wide power band, examples that come to mind are the early Taurus SHO V6 and a certain AMG unit known for head bolt issues.

Anything that sticks out of the hood is gonna be the best though, even if the runners are technically too long. Just saying.

The correct answer is always to go full Sonoramic Commando

Damn Ain't seen one of them For Years.  A fellow up the Street has one in  his Plymouth , It has a plaque in the  Dash that say's "Not Intended For Street Use"

The plaque might say it's not for the street, but that's a torque producing intake manifold.  413 Max Wedge might have been hot, but notice how they didn't keep it around for their top street/strip engines.  

barefootskater said:

The general rule is short runners are good for high RPM and long runners are good for low-end grunt. Lots of engines actually have variable length runners for a nice wide power band, examples that come to mind are the early Taurus SHO V6 and a certain AMG unit known for head bolt issues.

Anything that sticks out of the hood is gonna be the best though, even if the runners are technically too long. Just saying.

one of my favorite examples of variable runner legths is the 4 rotor 26b that i think was in the 787b race car. it has sliding velocity stacks that would change length based on engine speed.

In reply to SkinnyG :

My first thought was man that's a large plenum but once I did the math it's not that big.  I'll do more research tonight. 

Runner length tuning also depends on what order wave you are targeting. 
Handy basic calculator that ignores some of the details like valve timing - http://www.bgsoflex.com/intakeln.html

You may have pooling issues cold but once the engine is warmed up there shouldn't be any trouble keeping it vaporized. Backfires in the intake may be something to consider when you have a few liters of vaporized fuel in a plenum. 

those long tubular runners, all evenly spaced like that, are only a small bend and a rolled bead on the end away from being perfect for motorcycle carbs or throttle bodies...