So - 2002 Magnum 360 with OE manifolds. I'm pondering a small increase in exhaust tube size from the manifolds to the y-pipe for the best overall efficiency and low end torque between 1700-3000 rpm.

In the OE configuration the engine had 2" main exhaust tubes between the manifolds and y-pipe, and it's all old and rusty so I'm replacing it. Nothing major done to the engine - just freshened up a bit and with a bit bigger truck Comp cam (212-218 (264/270), .480/.480, on a 114* LSA), plus an Eddy 7577 intake and 2bbl Sniper, but other than that pretty much stock.

Truck is being used as a 'truck' - lots of off-roading, mild towing, occasional drives to work, but no racing - the engine likely won't ever be at/above 5000 rpm, except maybe for just a few seconds when passing. Mostly in the 1700-3000 rpm range.

Pondering if there are any tangible benefits to going with slightly bigger main tubes from the manifolds to the y-pipe, like 2-1/8" or 2-1/4", or would the engine operate with the best efficiency and low end torque at the factory spec of 2". It's probably too 'subjective' of a question...but there it is.

If going to 2-1/8" won't hurt the bottom end then I'll go that route, and if 2-1/4" will be help it breathe down low then even better...but I don't know that to be the case, and several calculators indicate 2" to be just right for this engine.

Thanks for any thoughts or recommendations.

I think it would pick up some power from improved breathing, based on similar up-sizing others have done.
I've done it myself, but those cars weren't dynoed or drag raced; seemed to pick up a bit of power.
On my drag car with 3" collectors, went to a 3.5" X-pipe exhaust with Race Bullets, dumping at rear axle, didn't slow the car down (Decibel rule at Sears Point).