Q1.Is it worth the time, effort and money changing the catted centre section to a straight-through, with no other mods to the standard exhaust system (MY97)?
Q2.And if it is, what's the likely scenario come MOT time?

 

1) No. d/p and b/b show the best gains.
If you have to leave a cat in i.e. don't want a catless d/p, then replace the centre AND b/b together.

2) Will probably pass OK on the front cat only if you warm it up nicely and get your friendly MOT tester to do the emissions test first.

 

As Dave says it's not really worth just changing the centre.

If it's noise you're after change the backbox.

If you want performance change the downpipe.

For minor gains and noise, change the centre and backbox.

With the standard downpipe cat in place, it will pass without warming up!! The P1's for example only have the front cat in place, and the PPP cars have a catless centre, but retain the downpipe cat.

Front cat - cold start cat
Centre cat - warm running cat

If you changed the downpipe and retained your centre cat, you would need warm up the car prior to an MOT test, providing your centre cat is in good working order.

My old car a MY97 Uk car, had a Scoobysport downpipe, Scoobysport backbox, and the standard centre. Whent he car was warmed up, it failed the idle emissions test, but passed the fast idle (2500rpm) emissions test. The fast idle test is only done, when the car fails an idle test. Either way my old would have passed an MOT!

Hope this helps
Andy

 

Yes thanks it helps a great deal.

 

Yes thanks it helps a great deal.