Already have a Ninja rear box fitted, and I am considering replacing the standard centre pipe with an aftermarket one, obviously....will it make much difference to the overall performance..or even more important, will it just make the car even louder

 

If you go for a straight through magnex centre pipe or similar then your exhaust will be noticeable louder whilst performance is increased very slightly. If you put in an aftermarket with resonator then no changes will probably be noticeable.

 

....in my opinion you will be much better replacing the standard downpipe with a decated open neck one.
I did this when i had a ninja backbox. The exhaust note will be much more grunty and deeper and the power increase much more noticable ( approx 30 bhp more ). I would then replace the centre section lastly if you want to go full decat.... the exhaust tone will then go alittle deeper again but will not add much power.
I ran a Hayward and Scott open neck downpipe with a Ninja backbox, then added a H&S centre section.

If you do eventually go full decat....get a knocklink to be on the safe side, it will let you know if your running too lean.

 

i have a my99 uk with ninja backbox, decat centre and apexi induction i got 249 bhp on pe rollers and 246lb of torque

 

is the knocklink essential? if you are running too lean, what can you do about it?

So a de-cat down pipe and back box is preferable for gains rather than a de-cat centre and backbox.

 

No, you might be lucky, and it'll be running O.K, but if it's lean on WOT it's only a matter of time before the engine pops.

Stop running it like that until you have found out why it's running lean and fixed it. Amongst many other things it could be that the fuel pump is tired, MAF or lambda sensors are old and tired or that you need a re-map.

 

since fitting my full decat exhaust my car pops and bangs after whilst heavy thrashing and even shoots flames when reving. doesnt this mean its running rich not lean?

 

...A full decat will give you about a 40 bhp gain.
30 bhp coming from a decat downpipe and most of the rest from the centre section.
A knocklink ( approx £120 ) will give you some advance warning if there is a problem with the engine running lean...thus saving an expensive bill.
However, i had no problems with my fully decatted MY00...just the odd green light flickering occasionally.
Best thing you can do after a decat is to get a Tek 3 remap if you have a 1999 or onwards model which will iron out any problems as well as turning your Scoob into a completely different animal..

Bob Rawle at BRD who remapped my MY00 UK turbo strongly suggests you get a knocklink if you have a decat.

smurfy.

 

so i get

1) a full de-cat
2) a knock link
3) if i have any probs i get bob round to remap/get bob round anyway

 

So would I be ok running a centre section and rear box? Or would i need a knocklink also? I can't fully de-cat it yet as "officially" its still under warranty and I also dont think the missus would be too imprezzed!!

 

couldnt you put the standard back on if you needed to get any warranty issues resolved?

 

That is the idea SpoonZ for when it goes for a service or - touch wood - amything else......

But with just those modz, would I need the knocklink?? Ive got a chance to purchase a H&S centre section this week, but dont want to buy it and then find out that its gonna cost me more money again 'coz i need a knocklink.

 

Whilst I agree the downpipe is the biggest contributor to the power gain, I'd suggest 30bhp from changing the downpipe alone is somewhat on the optimistic side for a standard or near standard scoob. IMHO, the bigger benefit of changing the downpipe is to spread the power - improved spool up giving a lot more torque at e.g. 2500rpm, and power carrying on a little better at high rpm too.

Also, I support the idea to get a re-map as well as the downpipe if funds allow.