[TurboKraft]

Hi Goran,
That's very true, the turbine blades are the major cause of backpressure.
But I have also seen modified engines wake up and become more responsive, more powerful when removing headers with little 1.5" OD primary pipes and going with larger 1.625" or 1.75" primaries and larger secondary pipes.
On a mostly stock engine, or something <400hp, I don't think the big 1.75" headers make sense, no.