Questions about decats...

macaroni · Post by **macaroni** » Fri Jun 01, 2007 8:50 am

I am planning to fit a decat to my car.

Do I absolutely need to refit the lambda sensor, or can it be left unconnected, monitoring fresh air?

If I do use it, will the car pass an MOT without the cat?

It is a 1994 480 turbo, by the way.

Cheers,

Antony

JohnTurbo · Post by **JohnTurbo** » Fri Jun 01, 2007 9:24 am

You need a CAT to pass an MOT post 1992.

Lambda you can unplug totally, but better would be to plumb it into the decat.

macaroni · Post by **macaroni** » Fri Jun 01, 2007 9:45 am

Thanks for the reply.

I know you need a CAT, but I know of some, n/a admittedly, cars that will pass a CAT test with a decat pipe in place.

Can you tell me in what way it will be better with the lambda plugged in? Power? Economy? Emissions?

Cheers,

Antony

JohnTurbo · Post by **JohnTurbo** » Fri Jun 01, 2007 10:49 am

Economy. Without it the engine runs a litle rich to be safe.

Its possibly you'd pass without one, but i'd say it was quite unlikely. (emissions wise)

macaroni · Post by **macaroni** » Fri Jun 01, 2007 11:16 am

OK, cheers and last question; is a decat worth the bother?

I had a custom made one fitted to my Xantia Activa and, albeit with an MBC fitted also, I couldn't really find any improvement with a decat.

98kellrs · Post by **98kellrs** » Fri Jun 01, 2007 11:36 am

For a 94' turbo I'm not sure. I could almost certainly say that you'd notice the engine 'breathing' better, things would feel less restricted however, being a 94' you would definately need to bung the CAT back in every year for your MOT...so I guess it depends whether or not you can be arsed to do that every 12 months

crispy-d · Post by **crispy-d** » Sat Jun 02, 2007 1:28 am

You will need a cat on there for the MOT - it will fail the emissions without it as they're pretty strict on the later cars.

dragon · Post by **dragon** » Sat Jun 02, 2007 1:55 am

JohnTurbo wrote:You need a CAT to pass an MOT post 1992.

crispy-d wrote:You will need a cat on there for the MOT - it will fail the emissions without it as they're pretty strict on the later cars

These comments read as if you're saying "if you don't physically have a CAT on the car, you will fail regardless" (and apologies if thats not what you guys meant). This is a fallacy (sp?) that even I believed until last month, then I was told I could decat my V70 as it was on LPG, and I didn't believed, so I took some light bedtime reading in the form of the MOT rules and regs.

There is NO test for the presence of a CAT on ANY car, as long as your car can pass the emissions tests, you pass. IF you can get your emissions OK without a CAT, you pass, regardless of the year.

Unfortunately, I'd wager you wouldn't get your emissions low enough without one.

crispy-d · Post by **crispy-d** » Sat Jun 02, 2007 1:36 pm

Sorry, I didn't make that very clear - I was tired and grumpy!
I meant that whether the car has a CAT or not, it has to pass the emissions, obviously, and without a CAT the turbo engine won't pass the emissions test.
I took readings with and without the CAT on when I got my hands on an exhaust gas analyser, and with the CAT it read 0.0% When it was off it read quite a bit above the threshold for passing. Yes, you can turn the CO adjustment down, but I tried that and it threw out the lambda reading then!

Best thing to do is have a CAT ready for each MOT! Can't go wrong then.

robkendall · Post by **robkendall** » Sun Jun 03, 2007 8:24 am

macaroni wrote:OK, cheers and last question; is a decat worth the bother?

I had a custom made one fitted to my Xantia Activa and, albeit with an MBC fitted also, I couldn't really find any improvement with a decat.

the 'innards' of a cat are basically a honeycomb block yeah?
so they restrict exhaust gas, making it go through lots of little holes where the 'cat magic' does whatever the heck it does.......
remove this and the exhaust gas flows straight out.....

ok, so basics done lol....on a turbo, pretty much rule of thumb....the quicker you get gas out, the free'er the engine runs....as i understand it, force aspitrated cars dont rely on back pressure, so no restrictions = better performance?

rgrds
rob

hjkort · Post by **hjkort** » Mon Jun 04, 2007 9:09 am

without CAT, it can and will comply to the regulations concerning the emissions. BUT, on the car's paper, there's a code which tells if the car must phisically have a CAT. It will fail MOT when it's not fitted.
Wheter the CAT works (and the material is still inside te CAT) can only be tested with the 3-gas tester.
On a closed loop management, older cars with milder regulations will comply.

JohnTurbo · Post by **JohnTurbo** » Mon Jun 04, 2007 11:09 am

Dragon is right. I'd previously been told by an MOT tester its not allowed to remove a cat, but if you can pass without one, then it doens't matter that you don't have one. IE they can't fail you for having no cat, if your emissions meet he standards.

Saddly i struggle to get my volvos through WITH cats.

ozturbo · Post by **ozturbo** » Tue Jun 05, 2007 7:16 am

My exhaust guy fitted a high flow cat to my turbo and it has made a big difference to the performance. Universal cats are made here in Australia by Walker which can be fitted to most cars and they come in standard and high flow versions. I don't know if they export them. Do you have exhaust specialists in UK?

dragon · Post by **dragon** » Tue Jun 05, 2007 5:39 pm

JohnTurbo wrote:Dragon is right. I'd previously been told by an MOT tester its not allowed to remove a cat, but if you can pass without one, then it doens't matter that you don't have one. IE they can't fail you for having no cat, if your emissions meet he standards.

Saddly i struggle to get my volvos through WITH cats.

You know what to do then JT - eat beans and GAS it up. The V70 has no CAT at all now

Makes for a nice note with the new 3" system.

macaroni · Post by **macaroni** » Mon Jun 18, 2007 7:08 am

OK, so I have a acquired a lovely S/S decat pipe, but it has no lambda sensor hole in it. The cat has a squashed part at the front, through which the lambda sensor is screwed. It doesn't appear that the lambda probe is long enough to do all the way through the diameter of the decat pipe.

Anyway else had this issue?

Cheers,

Antony

martinholmesuk · Post by **martinholmesuk** » Mon Jun 18, 2007 7:11 am

macaroni wrote:OK, so I have a acquired a lovely S/S decat pipe, but it has no lambda sensor hole in it. The cat has a squashed part at the front, through which the lambda sensor is screwed. It doesn't appear that the lambda probe is long enough to do all the way through the diameter of the decat pipe.

Anyway else had this issue?

Cheers,

Antony

Think thats normal regarding the sensor. I think/thought the thread was M18 COURSE but after buying the nut the sensor would not screw in

macaroni · Post by **macaroni** » Mon Jun 18, 2007 7:22 am

Thanks for the reply Martin.

So did the sensor go all the way thought the decat pipe?
I'll probably get a garage to drill it etc, but I just want to make sure it will work before giving the car to them.

As an aside, is RichP still around? I sent him my ecu on 5/6/07 and have heard nowt from him, I just want to make sure he has recieved it.

ozturbo · Post by **ozturbo** » Mon Jun 18, 2007 7:33 am

Martin, I like your avatar. Talk about "ouch"!

macaroni · Post by **macaroni** » Tue Jul 03, 2007 6:34 pm

That comment sounds a bit daft now eh Ozturbo?

Well I had my decat pipe fitted, at great expense, without the lambda sensor for the moment and can't really tell the difference. I am running an orange ecu (car is '94 model), but I just received my blue ecu back from Rich, so I'll try that.

So hopefully, I'll have a Richmod, decat and a couple of turns of an MBC to turn my car into a beast.