The reason I've been told they work so well is that the runners are about as close to an ideal length as you can get with an OOTB intake. This is from Don Dulmage's website http://www3.sympatico.ca/big-d/index.htm

" Tuned length of an intake runner.
Runner length is not an exact science because of the variables involved but a rule of thumb formula I often find handy for sorting out manifolds is from Philip H Smith (Tuning For Speed) It states that:
the intake runner should be approximately equal to 90 divided by the RPM in thousands
or
90/rpm in thousands = length in inches

ie for 6000RPM 90/6 = 15 inches

ie for 7000RPM 90/7 = 12.85 inches.

The measurment is taken from the intake valve to the plenum area. If your current 440 Mopar manifold seems too short now for your RPM range you're beginning to get the picture. "

CrAzYMoPaRGuY if you read the 2x4 section of the site he especially likes the 6pak Weiand T-Ram that he converted to 2x4 which looks like the one you have. Lots of good budget minded info on the site.

Kevin