To de-cat or not to de-cat. Questions please.

[SeanyD]

Hi Folk

Anyone de-catted their Elise, and familiar with before and after? Questions are

1) Any notable difference in performance?
2) Any notable difference in noise?
3) Any issues come MOT time? Does it pass, does it need temporarily removing, does it need the assistance of a 'friendly' tester?

Any advice, either Elise specific, or other vehicles, much appreciated.

Vehicle is an s2 k series, Induction, and Larini clubsport exhaust.

Thanks in advance

Sean.

[Mr_C]

1) No
2) Yes - it drove me mad to I put the cat back in!
3) Errr....

Edit: I should have said - it's a standard S1 with Larini ClubSport, Piper 421, K&N. It sounded ACE when you were pressing on but the drone on the motorway drove me up the wall.

Edited by Mr_C on Monday 21st September 10:23

[edo111s]

MOT issues and potential invalidation of insurance would put me off, no matter how great the car might sound …

[chris7676]

No. Don't think you gain anything except for more noise (though not the character of it as you do due to lack of airbox) and technically being illegal.

[purpleperil]

chris7676 said:

No. Don't think you gain anything except for more noise (though not the character of it as you do due to lack of airbox) and technically being illegal.

And flames - don't forget the flames

[JTBUSH]

DE Catting is not illegal. Having a CAT is not a legal requirement. Passing an emissions test come Mot time is a legal requirement. Passing the emissions test without the CAT is not going to be easy, but not physically having the CAT wont make you fail. IE, your failure wont be down to "CAT Missing". Just down to emissions fail! You could in theory have a very clean running engine and not have a CAT and pass the Mot

[bogie]

A common question, and answered most weeks for many years...theres a good techwiki on such things at www.seloc.org

Pros n Cons

Pros - tiny bit more power released on high powered tuned cars, measurable on a dyno 3-4bhp maybe, not noticable from your arse dyno unless you have a sensitive bum of course

Sounds a LOT louder (good or bad thing depending on your view)

Cons - will fail mot, so you have put it back on each year (or pay someone too)
- will be too loud for many trackdays - you have to put it back on again
- may get unusual smells in the cabin, make some passengers feel sick
- rear clam gets blackened and requires cleaning regular around exhaust exits
- dubious legality (although never heard of anyone getting anything other than a rectification order)


save up and get a sports cat, would be my advice......you get the 3-4bhp gain, better sound, but without all the downsides ....but costs 4x as much .....

[SeanyD]

Thanks folk, especially bogie, for the responses. Sounds like too much of a PITA, and the Larini makes the car loud enough to start with, so probably not going to proceed.
Thanks again,

Sean.

[TonyHetherington]

Seany - click the videos in my profile, I have a comparison of std vs larini vs larini+de-cat, which may help.

I must admit I grew to like the noise of the Larini (in fact it's the best note I've heard ) but then de-catting it I did with a little trepadation. However, all it did was make it slightly louder, give me flames (rarely, but brilliantly) and a little more "roughtiness". It wasn't a massive change, but it was definitely worth it.

For the £70 or so all in that it cost it was worth it - and to be honest it's pretty simple on an elise to change the cat/de-cat over. Jack rear wheels up, take off undertray, unbolt old one and bolt in new one. As you have a larini in there the bolts on one side will be ok anyway, and you may be lucky with the others also.

I'd recommend doing it, I really did like mine, and only once or twice had the MIL light come on but it then went off after a couple of restarts.

Come MOT time it's an hour's job to swop the cat back on again and get it MOT'd.

[Gad-Westy]

Hi Sean. Long time, no see.

My car is normally decatted. I put the cat back on the other day for an MOT and the difference in noise was very noticable and really dissappointing to be totally honest. Each to their own on this front but I feel that the decat injects some character into the soundtrack. When I put the cat back on the car sounded wheezy to me. So on the noise front, I'd say thumbs up with the caveat that it is louder and if you already feel your car is loud enough or too loud it may not be a wise move.

Performance wise, I can't say that there is any improvement. At the time I fitted it I felt that the car felt a little more keen to rev and for a short while I appeared to have improved MPG but I think these are just coincidental as putting the cat back on seems to have no discernible affect.

The car will not pass an MOT with a decat. It will fail on emissions, though having no cat fitted is not an offence in itself. Swapping the cat on and off an S1 takes about 30 mins and ideally requires the rear of the car to be up on ramps. Guess an S2 is more or less the same.

I'll be fitting my decat back on in the next couple of weeks or so. If you want to hear a before and after.

[chris7676]

I have also a S1 111S, tried both (cat out and in), and don't agree about more noise character. You need to get rid of the airbox to get the character, otherwise it's just loudness. Not worth bothering unless you have a very high powered car perhaps...

[TonyHetherington]

I mus tadmit, the S1 111S compared to S2 111S larini exhausts are very very different.

[Gad-Westy]

chris7676 said:

I have also a S1 111S, tried both (cat out and in), and don't agree about more noise character. You need to get rid of the airbox to get the character, otherwise it's just loudness. Not worth bothering unless you have a very high powered car perhaps...

Its not just volume although that does increase, its the pops and bangs and the change in noise on the over run. Each to their own, but I love it. Putting the cat back on this week revealed just how different the car sounds without the decat.

Agree about the air intake being important but then you could argue that just increases the noise of the induction air. Both are good mods in my opinion.

Edited by Gad-Westy on Wednesday 23 September 16:53