Quote:
Originally Posted by bjun
And wouldn't straight pipe mess with back pressure?
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Quote:
Originally Posted by Sportsguy83
For turbo, you want the LEAST amount of backpressure possible so removing the cat is actually a great thing.
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For NA you also want the least amount of backpressure. It's all about pressure wave tuning, backpressure happens to be an undesirable side effect of pipe size in some (most? all?) applications.
With turbo you want essentially no exhaust behind the turbo (really a conical diffuser for best performance), with a good pressure differential across the turbine. That's why turbo cars usually run smaller exhaust runners than NA versions of the same displacement. In the particular case of our cars with stock header/PTuning turbo, there is likely a pressure drop across the catalyst, so it would make sense going to a catless header would improve performance. You ideally want the pressure drop across the turbine, not before it.