I’ve done a back to back test of normal length headers vs the 42”-ish primary length Hooker fenderwells at least twice(that I can think off the top of my head).
Both strokers....... both lost about 40hp by installing the fenderwells.
They weren’t 2-1/8” fenderwells though.
I also remember testing a SR headed 446 with a .625 lift roller cam with the owner’s fenderwell headers....... which were the only headers we tested it with, but I remember thinking it was down about 40-50hp from what I would have expected.
Where the long primary length excelled was in pumping up the TQ numbers below peak TQ.
At the beginning of the pull there were a few lines where the longer primaries were up about 40ft/lbs.
