I have SS B Box and a Down pipe but have still retained the centre cat.

With the DP I notice a nice turbo noise and much easier to drive at low revs and I need less trottle to pull away from stand still.

I didnt notice massive difference in acceleration but do get slightly quicker spool up and a little better breathing close to the red line. I guess this translates to better performance overall only hard to meansure subjectively.

Will I notice a big difference if I replace centre cat with a straight through mid section?

Derek

Yes you will make a considerable gain. When I put my centre cat back in it completely strangled the car.