Both are available through No Limitz, among others.
4-1 and 4-2-1 are 2 different design concepts on how to get the most flow (for power) in a given space.
In general, more depends on the internal flow quality than the actual number. Also, one needs to have a proper structural desgn within the design concept.
Also, whether or not a vehicle is blown (turbo or supercharged) makes a difference as to what one wants in a design.
In a normally aspirated engine, you need SOME back-pressure for mid-range power and torque. Torque is often overlooked in power increase mods. Many mods simply move the horsepower and torque around within the powerband (more high-end comes at the expense of mid-range). So, one that gives great full-band increase may have less maximum power than another product.
For a blown mill, esp. one with very high horsepower, back-pressure is less important and can even be "bad," as the forced induction flows different than normally aspirated.
The engineering of a design tries to balance numerous factors to optimize some elements at the least able deficit to others, while others try for a more "across the board" improvement but without the high numbers in one particular facet.
One "perfect" design for one application may be "over compromised" for another.
(That sounds long and rambling, but makes sense if one knows the topic.)
As for the brands . . .
I don't know the brands for the xBs very well, either.
I came from the Miata community, which is VERY different than the xB.
Anyone know the specifics between Strup and Weapon R?
