Ok - have a decision to make and I just can't seem to get there.

Curerntly have a '97 JDM v3 Sti fitted with various bit and bobs:

Apexi power FC
ITG panel filter / modified intake.
Parallel feed fuel rails.
Water injection.
Ninja backbox

I'm going to decat (just the one cat on mine in the D/P as its sti).

Almost certain I'm going for H&S ssystem and have been in contact with them recently.

Question is though I can do one of two things without loosing the ninja backbox.

(1) 3" d/p with flow splitter and centre section tapering to 2.5" for ninja backbox.
(this means I need to change d/p and centre section for MOT).

or

(2) 2.5" dp (I beleive this is 3" mouth tapering to 2.5"?) with flow splitter and 2.5" centre section
(this means I need to change d/p only for MOT)

Am I going to see any benefit with option (1) or am I just wasting my time with the 3" down pipe and centre section...

 

I may be wrong mate but I don't think you will see a great deal of difference. If your looking to go down to 2.5 then I can't see it matters whether thats at your first join or second.

The de-cat downpipe should give you a good improvement in spool up and and power.

Just one point though on MOT, if you have an import the MOT station won't have that car on their model list therefore it can go through without an emissions test I checked this with my MOT chap just last week

 

Cheers my thoughts also - think I'll go for 3" d/p tapering to 2.5" centre section - this also give the advantage of spreading the cost somewhat with the option of purchase of centre section being done at a later date.

Interesting to hear about the Emissions test - my MOT station definately tested mine last time - have the rules changed?

http://www.motuk.co.uk/manual_730.htm

 

make shure you don't forget the new sport cat model around as you won't need to mess around when its mot time

 

Not sure on exact MOT rules to be honest. Reading your link I think they must use the pre-91 non-cat rule as our models are not listed on the UK database.

My chap said he will put mine through without a cat, perhaps he's just being nice