I've heard that it's easier and less restrictive to remove the catalyst (catalytic converter) and to make a small flange that bolts to the exhaust flange after the turbo and run straight tubing from there.Personally, I *think* I'd keep the catalytic converter in the system or put a high-flow cat on if the OEM wasn't flowing enough air, but with the DPF after it I can't see how it wouldn't flow enough air when removing the DPF (but I'm certainly no expert).