Reducing downpipe I.D

[IrishDave]

Thinking of reducing my down pipe from 3" to 2.5" where it passes the propshaft, using something like this http://www.ebay.com/itm/Vibrant-2-5...f8088cc&pid=100005&rk=2&rkt=2&sd=201418236259, then going back to 3", as it is constantly rubbing and is really starting to annoy the sh!7 out of me. I have had a few exhaust places try and fix it but to no avail.
Question is will this hinder performance, how much of a restriction is it likely to cause?

 

[superkarl]

Strategic dent

 

[Prawn]

Heat it. Bash it. Be happy.

 

[IrishDave]

Already tried the strategic dent and still rubs.

 

[Tom93]

Shift the engine on the mounts...

 

[IrishDave]

Tried that also. I have pretty much tried everything. My last option is to reduce the pipe size, so I just want to know how much this will affect performance.

 

[IrishDave]

The only time it has not rubbed is when the oe manifold was still on the engine.

 

[vivalacoulter]

Strange, lots of people have gotten away with that downpipe. I suggest you give it another bash, eventually you'll make enough space.

 

[superkarl]

I know how bad can it be rubbing to not work with a dent.
What engine mounts do you have?

 

[aragorn]

why do you think gaining 1/4" from going from 3" to 2.5" will make a difference if a 1/4" dent wont?

Make the dent bigger if need be.

Many OEM exhaust systems have huge flats pressed into them to create clearance for things.