3.0SE De-Cat

J

JDM

Senior member
Been along to my local exhaust specialist in DOncaster today to pick their brains about upgrading the exhaust.

I fancy a quad conversion but dont want to try and make it something its not and dont fancy having to mess around with the battery well etc getting it to fit, although I have to admit CJ's does look rather good.

All im after is a bit more grunt and if I get a bit more power with it then thats a bonus.

They suggested the removal of the CAT's. The set that are about 1/3 of the way down the exhaust system before the resonators. The guy at Top Gear has a 330CI and has done this and said its made a big difference to the sound and power.

What do you guys think?
 
It'll deafen you and make just a little bit of difference to power.

You'll also likely need to put them back for your MOT to pass emissions tests.

imho better stick to aftermarket systems than just removing pieces.

EDIT - BTW - thanks for the compliment about my quad system :thumbsup:
 
We had quite a bit of doing this on the E46's. On the 330's with 4 cats, when we removed the lower cats it still passed an MOT, and was much better rev wise, so more BHP.

I take it the Z4 is the same, so 2 cats on the downpipes and 2 under the car. Personally i would have it where the lower ones are removed, but on flanges so just in case you need to put them back in!

This is my next thing to do, but after the headlights need to watch the pennies for a few err days :rofl:

Let me know, as i will be going down this same route :D
 
The 2nd Cats aren't monitored by lambdas, so should be ok to remove...

Im wanting to chop the rear box, but would love get rid of those Cats also! Both would probably farrrrr too much though! :P Chris, have you got any videos? I know theres loads on youtube, but you don't know what else is in there.

Surely 2 Cats and 2 tiny resonators will be enough?! :P :evil:
 
It will be louder, well the coupe was, so god knows with the roof down what it will be like :lol:

In the US they never had the 2nd set of cats, as their emission laws are different. But you dont need 4 cats! Well i dont :P
 
chris said:
It will be louder, well the coupe was, so god knows with the roof down what it will be like :lol:

In the US they never had the 2nd set of cats, as their emission laws are different. But you dont need 4 cats! Well i dont :P
Click to expand...

Oh yeah, i didn't realise that!! They just have a set of resonators instead. Get it chopped :thumbsup:
 
chris said:
It will be louder, well the coupe was, so god knows with the roof down what it will be like :lol:

In the US they never had the 2nd set of cats, as their emission laws are different. But you dont need 4 cats! Well i dont :P
Click to expand...

I guess one persons louder is another deafening :D

Isn't it the first cats that are missing on the US not the second? I have something in my mind that says the first set are only fitted for emmisions on start up wheras the 2 nd set take longer to heat up but dot eh main bulk of work and of course don't affect the MOT as the engine is pre warmed for that.
 
Na when we were looking into exhaust systems, the US dont even list cat replacement, as theres are on the down pipes. As you say these are the MOT ones, and not really sure why they bothered with the other two. But its good to get rid of them :D

It will be loud if going eismann etc, or milltek. Well anyone really :lol:
 
Just looked on realoem and the US is just a muffler where ours have the 2nd set of cats. But there seems to only be the rear box, no centre boxes at all? Is this why the rear box is so insulated?
 
Decats one of those things I'd like to be able to do and put it back in an instant if I didn't like it. Somethinng for someone else to do first :) (suppose that's only like me chopping headlights up, fitting diffuser, custom exhaust abd battery move, etc.)

I think my ideal would less restricted CAT and a vacuum controlled cutout, so I could get the nice subdued note of the large ///M backboxes and when needed bypass the lot for some fun
 
cj10jeeper said:
I think my ideal would less restricted CAT and a vacuum controlled cutout, so I could get the nice subdued note of the large ///M backboxes and when needed bypass the lot for some fun
Click to expand...
Same here - that would be my ideal (although not with the ///M backboxes :( ). A little bit more noise would be ideal...

Was Mr Whippy not planning to do something involving the electronic flap fitted to the 330Ci's backboxes? I seem to recall him picking up a cheap box to hack up but don't know how far he's got with this.
 
Hmmmm, some good / positive responses to this. I think im just gonna bite the bullet and do it. I suppose you dont know unless you try and I guess it is reversible if done correctly..

They guy is pretty tied up for the next week or so though, which is a good sign I suppose. He does know his stuff and I had him do a custom rear section on my last car (120d M Sport) which I was very pleased with.

He also mentioned about fitting a pipercross induction kit and a purpose made heat shield etc.. Not sure after reading the posts on here though that its really worth doing. If anything I may just mod the existing air box with a direct cold feed to the bottom, but Im unsure about this really. I do like the induction noise you get with a kit but would it be that noticeable as Ive already taken one piece of foam out of the sound generator... on the day I picked the car up :wink:

I just feel that the sound you get is just not that great for this type of car... I think what has made me realise it is driving the Z4 M around for a few days...
 
i think the sound is great with these cars, but the problem is you get used to it over time and crave more !
 
JDM said:
If anything I may just mod the existing air box with a direct cold feed to the bottom, but Im unsure about this really..
Click to expand...

Why would you do this? There is already a direct cold air feed from the front. Routing air from lower down could cause water injestion problems.

I have read however that there is a screen/flap in front of the Z4's airbox (many cars have them now) to take large particulates out of the air stream before the air filter. I removed this on a previous car and it definitely made a difference in responsiveness... Now i just need to find out whether its a bumper-off job!
 
easty027 said:
i think the sound is great with these cars, but the problem is you get used to it over time and crave more !
Click to expand...
I think you're probably right! It's never going to compete with a TVR speed-six engine, but I'm sure the 3.0 M54 can be made to sound a LOT better :)
 
There is an elbow behind the passenger side grill that I removed to get more air flow, will have a look tonight if there is any other bits to remove ha
 
Seeing a place on sat or monday for the idea to go quad, with lower decat. But on a flange so the cats can be put back if it fails the MOT. See how much they want, but seem very good, and great reviews so far :thumbsup:
 
Well im off to get mine de-catted (is that even a word) later this afternoon.

£30 per side so £60 all in for them to be removed and stainless steel bridge in place, then its straight from there to go pick up the new around for the weekend ( see other recent post ).

Ill let you know how I get on.

chris said:
Seeing a place on sat or monday for the idea to go quad, with lower decat. But on a flange so the cats can be put back if it fails the MOT. See how much they want, but seem very good, and great reviews so far :thumbsup:
Click to expand...

Chris, will be interesting to see what they say about the quad system, I still like the thought of that :thumbsup:
 
You must log in or register to reply here.
Back
Top Bottom