think its a metric size. i think i ended up going from 2" ID after the cats where i cut the resonator off, and the same on the flange before the muffler connection. (that was the only one where the pipe closer to the engine goes over the pipe further to the back. normal praticae would be to always have the previous pipe go into the following pipe. ? does that make sense?) then just worked it out from there to fit my cross over.

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