does a cat have to be at the front of the exhaust system? 3" dp question

[paultownsend]

a friend is selling one of these
http://www.ebay.co.uk/itm/VW-GOLF-MK4-GTI-1-8T-20V-AUDI-A3-STAINLESS-STEEL-EXHAUST-DOWNPIPE-DECAT-CAT-PIPE-/180902138959?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item2a1e9b944f#ht_970wt_653

but i would really like a sports cat too. I have an AGU, so it wont be throwing codes up, but i want to be hassle free come MOT time.

so i was thinking of getting one of these
http://www.ebay.co.uk/itm/VW-Golf-Mk4-1-8-20v-Turbo-Hoffmann-Exhaust-Race-Tube-/290751097967?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item43b21dac6f#ht_2180wt_823
well, one of the £15 ones from ecp

and welding in one of these
http://www.ebay.co.uk/itm/2-25-MagnaFlow-200-cell-Metallic-Sports-Cat-59925-/260797918034?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item3cb8c46b52#ht_6934wt_912

this will work out a lot cheaper than a milltek. and i have seen graphs of good results using the OE backbox.

but will having the cat in the place of the middle silencer be ok?

i was quickly measuring up today, and seeing if you could weld a 3" cat in to the first section of the DP. But i think being so far forward, it may knock on the chassis brace thingy. i will have to investigate further!

as usual, any thoughts on my thrifty mods would be great

[paultownsend]

im not sure if im allowed to post to other forums, but here was the graph. looks impressive for such a small outlay. £100 extra for the mid pipe and cat. And a few beer token for the local welder.
much cheaper than a milltek or any other off the shelf option

[golfyste]

Cats have to Be at the front of the system as they work off the heat. So placing it further back means it is less effective and may not get you through the mot therefor being a pointless restriction 

[paultownsend]

Good man!
I will get the measuring tape out and see If a 3" cat can go in the second section of the decat. Where the second lambda boss is

[shaft69]

That race pipe only 2"