[pHaTtYaSs2x4]

I've been looking for a larger barb inlet for my 1250(1/2" BSP) to maximize flow from my 2-342(3/4") heatercore. But i'm wondering, if the BSP is 1/2", is the largest effective inlet 1/2" ID? Cuz if i have a 3/4" OD(5/8" ID), wouldn't it just taper down to 1/2" ID since the BSP is 1/2"? I was also thinking about completely removing the inlet barb and fitting 3/4 ID tygon over it. Would that be big enough?

PS: Anyone know where to get plastic or nylon BSP fittings?