Re: Which manifold for 16v?
On my previous Minari (Tuned 1.7 8v), I had an 'adjustable' manifold made up by Maniflow in Salisbury. This paired no 1 with no 3 and 2 with 4 (left and right pairings). I could adjust the lengths of both the primary and secondary pipes by about 6-8" on each. When tested on a rolling road, the power and torque charactaristics could be changed markedly with different lengths.
I no longer have the test results (sold the car 5 years ago) but the general principle was that long lengths gave better torque (lower down the rev scale) and shorter primaries gave better ultimate power, but at higher revs.
I used 2 settings - One for hillclimbs, where pulling torque out of hairpin bends was most important, and one for circuit racing where pure power on the straights was desirable.
I haven't tried linking opposite cylinders but I would like to know the results of any testing done elsewhere.