I've been curious about primary diameter. Every set of headers you see is made for the 318 or larger, and always start with 1-5/8" primaries. However, the exhaust port dimensions on a 273 head equate to just shy of 1-1/2" circular. I have only seen 1-1/2" primaries on headers for the V8 Dakotas, but I think those are magnum heads? Anyway, since I have no interest in trying to turn my 273 into a screamer, I just want the better torque of appropriately sized primaries.
Until, then I will keep my stock manifolds.
