Is it an issue to run a standard 2.5” downpipe into a 3” catback system? How would the two different sizes fit together and would the doughnut gasket still do the job it was designed to do when it was sealing two 2.5” pipes together?

Reason I’m asking is that I may be able to get my hands on a Kakimoto ‘R’ cat back system for a very good price. Only problem is it’s a full 3” diameter pipe and does not taper down to 2.5” where it will meet my standard DP.

Personally I wouldn’t of thought 0.5” wouldn’t cause too much of an issue but I’m just looking for reassurance & advice as I don't want any leaks.
Thanks

 

I'd buy the 'R' and get a 3" downpipe when you can and fit it all at once.

 

This is what I plan to do at some point but rather than a simple decat downpipe I would want one with a sports cat for MOT's and don't have the funds for that right now.

Is it a no go matching a 2.5" - 3" then?

 

anyone?

 

The issue will be 3" flange holes not lining up with 2.5" flange holes, so I doubt it.

 

didn't think of that. Is there an adapter available for this sort of problem?

 

A reducer will only work if there is enough room to add it.
If the Kaimoto centre section is the same length as a std section then this won't work.
Some exhaust makes have deliberately shorter sections with slip joints and adapters to allow this kind of mismatch when joining up to the std pipework (e.g. revolution 3")