Exhaust & CATs

[swlabhot]

I got a 98' 3.2L. If I get rid of the CATs:

1) Will it fail MOT?
2) Will I get a CEL? (Are the O2 sensors before or after the CATs?)

Is it going to be ear splitting loud to de-cat in addition to an aftermarket muffler?

[Ciaran]

Hi swlabhot,

a topical issue for me...I have just fitted a very beautiful stainless steel "Rice Rocket" from Mark J at Dali, to my 95 T (with only 120k so I cannot match Ben's figure..)

I had considered removing the CATs, but Mark advised that it is much louder....that was before I ran the car with the Rice Rockets....under 3k it is unbelievably loud & boomy (as if there was a hole in the exhaust), over 3k it is a joy to hear, a throaty roar, with a very distinct V6 sound, and it begs for more revs (which do seem to come quicker, but I think that may be perception rather than reality, only the next track day will tell)

So with an after market exhaust, it is going to be loud...

I may tempt the technology and try to post some pics of the exhaust install, as we did the job ourselves (no NSX service poeple over here....not that we miss them...so far!! :shock: )

Ciaran

[swlabhot]

Hi Ciaran,

Yes please do post some pics!

I wanted to remove the CATs as I believe it will improve throttle response and free up some hp but not sure if it will throw a CEL. If this is the case then I won't be removing it. I know it is going to be loud without the CATs but as I'm getting a custom muffler made up I can have the final sound 'taillored' with the De-CATs in place so if after removing the cats is too loud, I can have them make make/tune the muffler to quieten it down a little. Otherwise I won't be thinking about removing the CATs with an off-the-shelf muffler. The 'sewing machine', ticking, rattling noises from the oem exhaust is driving me nuts, IMO this is the only let down on an otherwise complete 'exotic' package, and so it has to go ASAP!

[jaytip]

to answer your first question,yes it will fail the mot with out cats.

[ctrlaltdelboy]

re MOT - it will not fail the MOT just because it does not have cats.

part of the MOT is the emissions test - by not having the cats in you risk allowing sufficient gases through the exhaust system (many of which would have been stopped/converted by the cats had they been there) to fail this test - in this case then yes, not having the cats in has caused you to fail the emissions test and therefore the MOT.

however if your tuning is sweet and the car is not running rich etc then you may well pass the emissions test despite having no cats - many people have passed with no cats.

the O2 sensors are positioned just BEFORE the cats (before as in gasflow direction).

other relevant threads on these subjects can be found using the search function which threw up the following:

http://nsxcb.co.uk/forum/viewtopic.php?t=539&highlight=cats

http://nsxcb.co.uk/forum/viewtopic.php?t=524&highlight=cats

http://nsxcb.co.uk/forum/viewtopic.php?t=159&highlight=cats

http://nsxcb.co.uk/forum/viewtopic.php?t=87&highlight=cats

[Pande]

Swlabhot I own a 3.2 and have had my cats removed. I chose to have two silencers made instead of straight through pipes. No warning lights come on as long as the sensors are positioned in the original place. You may find straight through pipes will create a tinny sound so silencers still ensure maximum air flow with a deeper sound.

If your ever in the yorkshire area come and hear for yourself or better still take the beast for a blast yourself.