De-catting

[philmccann]

Sorry to be a Numptie

But I've read a lot about de-catting / Pre-cats etc.

Why do you remove them, what are the pros & cons, how difficult etc?

Are there any MOT implications etc?

Ultimately, is this something I should be looking into?

Have a '97 Chim 4.0

Cheers

Phil

[spend]

Improve your search skills

http://www.pistonheads.com/gassing/topic.asp?h=0&a...

Dave

[thenick]

philmccann said:

Sorry to be a Numptie

But I've read a lot about de-catting / Pre-cats etc.

Why do you remove them, what are the pros & cons, how difficult etc?

Are there any MOT implications etc?

Ultimately, is this something I should be looking into?

Have a '97 Chim 4.0

Cheers

Phil

Hi Phil,

Cats are removed primarily to make the cars louder really, plain and simple. The pre cats are small cats, one in each manifold designed to reduce emissions until the main cat is warm and operatinng. Removing these can make the cars a little louder and perhaps gain a little power, though both are likely to be negligable but it is completely legal to do so and it will still pass an mot since the engine must be warm before starting an emissions test. The real gain is removing the main cat, this really has a dramatic effect on the exhaust note and volume and in my case had fantastic results and increased smiles per mile 10 fold. It can improve power though I don't know by how much, but the exhaust gasflow is noticably higher. The problem is that it now will almost certainly not pass an mot emissions test which can be a worry for some. To get around this, you can either buy a replacement y-piece and decat that and swap the cat back in for the mot which some do. Or buy a different system like I did from ACT which changes the big dustbin cat up front for two much thinner downpipes which can be removed very easily with a spanner and then these can be replaced with cats available from ACT. The other slightly greyer option is to find a 'friendly' mot tester who will help your car through its emissions test with the cats still removed. This is done entirely at your own risk, but is probably the easiest option of the three!

In terms of difficulty, its not too bad.. The standard y-piece must be cut open and the cat bashed out before it is re-welded, usually with a non-reversal cone in it to retain back pressure and stop the exhaust note sounding hollow. An alternative to this is the ACT system, which replaces the manifolds and y-piece with stainless smaller bore tubes (to retain back pressure) with improved gas flow - this is pretty easy to fit if your manifold bolts come out ok (mine didn't!) and changes the exhaust note quite a bit, though it is much better IMHO and sounds amazing. Another alternative is the V8enhancements y-piece from Clivef on here which is a stainless replacement of the y-piece (same shape) but without a cat. This is a cheaper option than the ACT one as it does not replace the manifolds but it does the same job pretty much so its up to personal choice.

Ultimately its your choice if you want to do it, the pros are pretty much entirely the noise and general feel that you're driving a muscle car (small children bursting in to tears and running away as you drive past them etc - it has happened!), and probably some bhp gain though i'm not sure how much (I think Tim said the ACT system gains around 20bhp/torque but I have not confirmed this). The cons are of course the issue of what to do when mot time rolls around, though its not that big of a deal and some have said that police have had a word with them about the noise. Having said that, i've had mine decatted for about 8/9 months now and I drive it every single day out of Birmingham city centre, where there are more police cars than i've ever seen anywhere else and i've never had anything from them at all apart from the odd thumbs up. I think they just assume that a TVR is meant to be that loud as once I was pulled for my small front number plate and after advising me to get it changed at some point he commented on how lovely it sounded - great stuff!

Here's what mine now sounds like:

http://s141.photobucket.com/albums/r65/thenick100/...
http://s141.photobucket.com/albums/r65/thenick100/...

Do it, you know you want to!

[philmccann]

Phew!!

Thanks for taking time out to write that, Nick

Appreciate it

Cheers

Phil

[thenick]

No worries! Was a bit bored with it raining outside and all, hope that helps a bit...!

edit - oh one more benefit, it dropped my running temp by 10 degrees across the scale, so now it sits no higher than 80 in traffic even in the middle of summer (well when it was hot I mean).

Edited by thenick on Saturday 8th December 18:33

Edited by thenick on Sunday 9th December 13:21

[Pasco]

philmccann said:

Sorry to be a Numptie

But I've read a lot about de-catting / Pre-cats etc.

Why do you remove them, what are the pros & cons, how difficult etc?

Are there any MOT implications etc?

Ultimately, is this something I should be looking into?

Have a '97 Chim 4.0

Cheers

Phil

Remove them yes.

Do you intend to do this yourself ?
But for what ever reason get shut of them as they are a bag of Shite

Pasco

[philmccann]

Hi Pasco

Yes, The idea would be to do it myself. Just need to work out what bits required and all the ins and outs before attempting it.
Just so I know exactly what I am attempting to do.
All new to me, this.

Cheers

phil

[thenick]

Are you planning to decat the original y-piece or replace with an after-market version?

Your options are

1. Cut & shut original or ACT can do it for you - http://www.actproducts.co.uk/silencing.php (ACTMS04 Griffith 500/Chimaera "Y" piece, gasflowed(without cat)) £235 +vat (stainless)
2. ACT stuff - same page as above (ACTMS13 New ACT performance manifolds, TVR Griffith / Chimaera , non cat, inc "Y" piece, with facility to fit cats at a later stage.) £795 +vat
3. V8enhancements SS decat version of the original - http://v8enhancements.co.uk/ £470 inc vat

[spend]

or a few quid for a cold chisel & lump hammer.....

Don't hack out your main cat until you have a spare to pass MOT with

Dave

[Bomber Denton]

Don't forget if you remove the main cat you need to alter fuel programming. You can change the tune resistor in five minutes for about a fiver to run 'pre-cat'

It does make a difference.

[chrispitman]

I have a de-cat Y piece I brought back in the summer but have not fitted, my manifolds have been de-catted and coned. It passed the MOT on just the main Y Catt fine a few weeks back.

If I change the man Y cat for my de-catted piece what value dose the resistor have to be changed to, also what dose this do is it to add more fuel, also apart from it becoming louder what else should I see, ie better free reving without the cat blockage is there any power gains.

[Boosted LS1]

I had an interesting conversation with an mot tester recently who said that if he was told that the engine was pre 1991 or whatever he has to accept that as a fact. He once tried to call dvla or vosa about an engine he was testing and they told him to accept it was an early engine and just pass the car. Interesting stuff.

[Bomber Denton]

Boosted LS1 said:

I had an interesting conversation with an mot tester recently who said that if he was told that the engine was pre 1991 or whatever he has to accept that as a fact. He once tried to call dvla or vosa about an engine he was testing and they told him to accept it was an early engine and just pass the car. Interesting stuff.

boocks. If the engine is pre-92 you need to have documental evidence i.e. letter from manufacturer fo it to be able for a non-cat test.

Failing that it goes for a cat test.

[spend]

Now the manufacturer is defunct, and the records are not available, it would seem a grey area? In the absence of a letter (which Gaydon will/can not issue for TVR engines) I don't think there is a provision in the law as it reads to make exceptions, even tho that might be a sensible approach?

BTW unlike me, Mike does not talk b011ocks, but he does a good rendering of gibberish when distracted by particularly well endowed barmaidens

Dave

[Bomber Denton]

spend said:

Now the manufacturer is defunct, and the records are not available, it would seem a grey area? In the absence of a letter (which Gaydon will/can not issue for TVR engines) I don't think there is a provision in the law as it reads to make exceptions, even tho that might be a sensible approach?

BTW unlike me, Mike does not talk b011ocks, but he does a good rendering of gibberish when distracted by particularly well endowed barmaidens

Dave

O.K. then I did my MOT refresher course last week and VOSA told me unless documental evidence is produced test to the age of the vehicle - no grey area?

[Boosted LS1]

Bomber Denton said:

Boosted LS1 said:

I had an interesting conversation with an mot tester recently who said that if he was told that the engine was pre 1991 or whatever he has to accept that as a fact. He once tried to call dvla or vosa about an engine he was testing and they told him to accept it was an early engine and just pass the car. Interesting stuff.

boocks. If the engine is pre-92 you need to have documental evidence i.e. letter from manufacturer fo it to be able for a non-cat test.

Failing that it goes for a cat test.

boocks to you as well mate. I've never needed any documentation so you're clearly wrong on this point. I say again that he said that when he called vosa or whoever they were, they were completly unhelpful and told him to accept what he had been told. There's no way he/they can verify an engine vin number as being pre 91 or whatever without support, presumably from dvla and they're not geared up for it. This tester has been in the business for years so knows his stuff. A similar thing probably applies to sbc's where everybody wants old blocks. Do you think these people have to produce a letter from GM, of course not. Who could be arsed to write it for them?

Whats more, if the engine meets emmissions requirements it doesn't need a cat regardless of if it was fitted with one by the manufacturer. I've tweaked all my saabs to pass the test without cats. They've all passed and whats more I can feel the extra power

It may pay to shop around before the test to get a more enlightened tester. This may be a bit like tv licencing saying you must provide your details when you purchase a tv from a shop when in reality you can tell them to knob off.

Edited by Boosted LS1 on Sunday 9th December 22:37

[Bomber Denton]

I'm a current tester and you are completely wrong - sorry.

[GreenV8S]

Bomber Denton said:

O.K. then I did my MOT refresher course last week and VOSA told me unless documental evidence is produced test to the age of the vehicle - no grey area?

Did VOSA specify what form of documental evidence is acceptable? Unless there's a standard format with traceability to approved issuing authorities, I don't see how any documental evidence could be relied on.

[Bomber Denton]

GreenV8S said:

Bomber Denton said:

O.K. then I did my MOT refresher course last week and VOSA told me unless documental evidence is produced test to the age of the vehicle - no grey area?

Did VOSA specify what form of documental evidence is acceptable? Unless there's a standard format with traceability to approved issuing authorities, I don't see how any documental evidence could be relied on.

To be fair it only needs to be a letter from manufacturer, which can be put together on most PCs

[spend]

I've suddenly unearthed old letters from Rover & TVR confirming that my engine is very old as I'm sure their records will confirm (if anyone can find them ).

Dave