Talking about primary tube diameters, look at Giulietta Veloce headers, they are absolutely tiny, does smaller diameter add a performance gain in 1300 cc engines. Most suppliers claim their headers fit, 1300, 1600 1750 and 2000cc engines, and no doubt they fit, but is a larger bore primary overkill on a small displacement engine? I know in race engines a smaller engine might benefit from bigger diameter primaries, I suspect, at least at the time Alfa knew what they were doing with veloce headers. Just wondering.
Cars ruined my life! 😱