I don't know for sure, but I always thought that it is just a measurement of the area of the inside of the exhaust ports. So, it seems to me that are wouldn't change no matter what turbo it is for. Just my opinion.
Derek
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1997 Dodge 2500 4x4 Ext cab LB 5 Speed, K&N BHAF, 5 inch turbo back , plate MIA, AFC tuned, bd 64/71-14, SDX 5x16s, boost elbow, 4K GSK, ARP head studs, oringed head, valair 13" full feramic clutch, autometer boost and pyro.