View Full Version : De-cat centre section

12th April 2000, 20:21
Hi chaps,
Just a couple of questions http://bbs.22b.com/ubb/smile.gif
I was thinking about a de-cat centre for my ukmy99, how would this affect emmisions-is the cat in the downpipe large enough to do the job by itself?
Also how much would it improve the cars performance? already have ss back box.



[This message has been edited by RobW (edited 12 April 2000).]

12th April 2000, 20:49
Rob I have just had a straight through centre pipe fitted to my MY99.

Emisions will be fine - my centre cat was removed by Prodrive 6 months ago as part of performance pack - they wouldn't remove it if it made it illegal! Prodrive replaced it with the STi '2 silencers'.

Performance wise, there will be quite a difference. Even just replacing two silencers with a straight through pipe has made a diffrence. The difference between a straight through pipe and a catted pipe will be at least twice as great, and will complement the S/S back box. (it also improves the sound track!!)

FYI - I shopped around a lot, and not many places still sell non-silenced de-cat pipes. The best option I found was a Scorpion two piece centre section/de-cat pipe. Bought from Motech (mail order) 69 + 9.99 P&P. Ask for David. Mail me if you want the number.

I am in Preston if you want to see/hear/feel mine.

12th April 2000, 21:13
Correct me if I'm wrong here, BUT, I thought the the MY99 cars, UK at least, didn't actually haver a centre cat....

IIRC, the reason for a centre cat was Japanses law, which required two cats to be fitted to vehicles... this was also responsible for the "cat on fire" warning light on the car....

Some cars have got resonator boxes fitted to the location where the second cat would have been; cutting this out can improve power / response a little bit, but aurally is quite, errr, "interesting" :)



12th April 2000, 21:58
Had my centre cat removed at scoobysport when I had my backbox fitted. With both the car certainly picks up quicker. The main cat alone will pass the MOT.

12th April 2000, 22:44

the car will just about pass on the centre section cat, if it's hot enough. The idea is you take it out for a blast, then immediately shove the exhaust gas analyser on it before it cools down.

FWIW, a good blast does incredible things to the exhaust.... apparently people following me [bravely, or foolishly :)] in the dark have observed an orange/yellow glow emanating from within my exhaust system! Should be enough to get any centre cat hot enough :) [not that I have one, that is].



13th April 2000, 12:06
The car may or may not pass on a centre cat alone. I have heard different stories ;) It will pass on the front cat as it certainly gets hot enough. I've never turned up for an MOT (appointment or not) and driven straight onto the ramp. I've also never had the exhaust analysis done first so the cat will have cooled.

13th April 2000, 13:04
From what I've been told - the centre/rear cat is a lot more restrictive than the front one. The front is an STi free flow, and is a lot less restrictive??

13th April 2000, 13:06
Motech's number - 01933 443390 - ask for David

Ian Cook
13th April 2000, 14:10
All UK cars have 2 cats, except the P1 which has a modded larger main one.

UK cars need the other one to pass the WVA tests on startup emissions, the Jap cars only need one, as they dont have this test.

UK cars will pass the MOT emissions test fine with the centre cat removed, i have mine tested just to see what difference it made, and the answer was none at all (emissions wise), i suspect if you removed the main one in the downpipe it would be a different story all together.

15th April 2000, 19:11
cheers guys,
Thanks for the info, will go for one when my new engine is run in first one only managed 5000k http://bbs.22b.com/ubb/frown.gif not bad for a brand new car eh!
Anyway that's all sorted now just a case of taking it easy for 1000k.

gary c, would like to hear your car but preston's a long way from herts http://bbs.22b.com/ubb/smile.gif maybe meet up at track day?


21st April 2000, 13:38

If you want to hear a UK MY99 with SS Dowpipe, SS BackBox and Magnex silenced decatted centre and Blitz Cone and Link ECU then i am in South London


Ian Cook
21st April 2000, 15:20
I have the centre secion and back box and am in Herts too http://bbs.22b.com/ubb/wink.gif