Small turbo and exhaust bore

[steve-V8s]

Was encouraged to change the exhaust downpipe and cat on a small engine turbo car for something with a larger diameter to reduce any restrictions. It feels as if the car has lost some low end torque. I was speculating that perhaps with a larger bore pipe the exhaust gas speed will be less resulting in a reduced turbo speed at lower RPM. Is that a valid thought or nonsense ?

[steve-V8s]

Ok I will dismiss that idea then.

My thinking was with a larger bore pipe immediately after the turbo the same amount of gas flow would have a lower speed and presumably a higher pressure.

Will look elsewhere for the disappointing loss of torque.