[RallyBob]

One thing about all the programs out there that calculate header design parameters....I've yet to see one for 4-2-1 designs. They all seem to be for 4-1 designs only. Apparently there are some variables with a 4-2-1 header design that don't calculate all too well. From what I've seen/heard, the best thing is to talk to someone who has done the development hands-on.

From my (very) limited experience with 4-2-1 designs, lengthening the secondary side moves the torque down into a lower rpm range. But I've personally never seen a 4-2-1 design that makes as nice a powerband as a well-sorted 4-1 design. I emphasize the 'well-sorted' because most 4-1 designs are far from optimal and are usually pretty horrid!