16V power hike query


New member
Hope you guys can help me out with this!

Not many people in the UK have a 16V BX with a cat fitted. Guess I'm lucky (d'oh!), but since my car isn'r required to have a cat fitted for its age ('92) I'd like to ditch it when I get a stainless exhaust made up.

My problem is this - 'cause nobody here has done it I have no idea what the effect would be of removing the cat on the way the car runs. I know I'll need to get the lamda probe tapped into the new exhaust to prevent it over fuelling but will I get the full 160BHP this engine should be capable of without the cat? Mine feels fairly strangled at the moment - I need more!!

Any advice or personal experience welcome



Alan S

1000+ Posts
Adrian has also been asking this question on an overseas board for BX Cits & has not had much response until someone was asking about turboing a BX Gti. These were the responses.

Alan S

Thanks... i'll take that under consideration
As far as stress goes... I think it has had enough
it is a 1992 8 valve gti with a power boost valve, K&N 57i induction kit, superchip and a straight through twin dtm exhaust and the catty removed...
but she runs well

Posted by Adrian on April 10, 2001, 1:00 am , in reply to "Re: 16v turbo manifold"

Did your car run OK when you took the cat off? I presume you've tapped the lambda probe into the front section for correct fuelling - was the chip needed to get it running properly as well?
Interested as my 16V has a cat but isn't required to have it!

Posted by gareth on April 10, 2001, 1:44 am , in reply to "cat removal"

Well it doesn't really matter if you superchip it, since you can remap the chip to take its readings before the cat and then when you take it out it doesn't really matter... some of them have the probe before the cat anyway (GOD knows why)

That's basically the entire conversation; not that we'd think of doing that, coz it's illegal ian't it?



New member
Adrian we here in Australia all have cats from 86 onwards, that means even the early Mi16's (cant speak for Cit's) have cats.
I *have met*
somebody who has removed the cat on their early 405 mi16, the O2 sensor is located on the downpipe, before the cat.
he replaced the downpipe with a mongoose exhaust which is made for a non cat car, then a hole was drilled into it for the sensor.
apparently he could feel a power increase or atleast greater throttle response and a deeper exhaust note, worth doing if legal.

"Any similiarites to an actual person or event is completely incidental and unintended"


New member
Thanks Andreas

I was concerned that there may be major differences between the cat and non-cat engines, and that just removing what is basically a big bung up the exhaust would cause it to run badly due to confusion in the ECU about where in the map it actually is.

I know that you need to tap the probe back in as on the cat cars this supplies the ECU with the idle fuel value which it automatically updates - no probe, and the engine thinks it's getting no fuel so chucks loads in. A local main dealer was happy for me to 'just take the plug off, it won't make any difference!'.

Having been out in Daniel B's modded 16V I think a stainless system will be on my shopping list soon, and then I'll see how it runs before deciding if I need to have the car chipped to sort out the fuelling. Normally the map is on the cautious side to protect the cat so it'll probably take more fuel with a chip - and hopefully more power too :)

Thanks again



New member
i assume your motor has a compression ratio of 10.4:1 as other UK mi16's have?
our's are 9.5:1 due to lower octane fuel, i have a UK spec motor though.
As long as your sensor is before the cat it shouldnt make any difference whatsoever to the ecu/fuelling, how can it if it doesnt know if a cat is there or not?


New member
A friend of mine works for a company as an engine developer and spent about 2 hours explaining how engine design has changed since the introduction of cat's on cars. Basically 'in the beginning' they simply bolted the cat on and modified the fuel map.

When they got more sophisticated they started to change the cam profiles to reduce duration etc to prevent fuel blow-by into the exhaust valves and hence unburnt fuel getting to the cat.

When you take a cat off an engine like this you end up with masses of fuel blow-by because the whole air/fuel mixture gets out of the engine that bit faster - so you get massive fuel bills and a car that runs like a pig!!

Good old Pug/Cit seem to have gone for the earlier option - but by the time my girlfriend's ZX was built they were doing the latter, so removing the cat isn't a great idea.

By the way, legislation in the UK means any car sold after 1/1/1993 needed a cat, and if a new model was launched after 1/7/1992 it also needed one. My BX is an 8/1992 so since the BX was a current model isn't required to have the cat. I guess that since Cit UK were the 1st owners they thought they ought to have one.

Happy 16Ving!