E85 Secondary Decat - What's Next?

J

jonathancaddick1

Member
Hello everyone,

I recently decided to try and get a louder, throatier, raspier sound from my 2004 Z4 3.0 and read somewhere that having your secondary (middle) cats cut out and replaced with straight pipes makes a difference so I went for that today, and there is a noticeable difference but it's left me wanting more!

It's not much louder than the stock system and I do occasionally hear pops and bangs but I'd love a more impressive, sporty sound when I put my foot down. I was wondering if anyone has any suggestions?

I dont want a muffler delete as this leads to drone, as (Ive heard) does removing the resonator, and I couldnt stand any drone.

I have also installed a cheap cold air induction.

Thanks! Jon.

PS. If anyone wants a video of the car with secondary decat, let me know.
 
I took the resonator with the secondary cats off and did 2 30mm bypass pipes on rear silencer along with a afe air intake . Been done over a year and no drone .
 
Are you in the uk?

Eu cars only have the cats in the manifolds then a resonator then the back box.
US cars had an additional set of cats i think but not sure.

Ive heard that removing the resonator shouldnt give you drone as its more the size of the piping you use.
 
I've taken one of the foam bits out of the sound gen, I found that both out was a bit too much but might try again with the decat now.

Yes I'm in the UK, mine definitely had the secondary cats, I have them in my boot to put back on in the case of MOT failure.

Heres a short video of the sound from inside the cabin at different speeds etc, as you can hear not a massive change but better than OEM I think.

https://youtu.be/-yULBQm4IFI
 
lotus791 said:
I took the resonator with the secondary cats off and did 2 30mm bypass pipes on rear silencer along with a afe air intake . Been done over a year and no drone .
Click to expand...

Lotus, when you say bypass pipes do you mean you removed the backbox and replaced with straight pipes? Or could you explain a little more?

Many thanks.
 
Can you show pics of your secondary cats?
Realoem shows secondary cats being replaced by the resonator which looks like a small backbox as opposed to two cats.
As for bypass he means a straight pipe going from befor ethe back box the exhaust tailpipe

Basically some gasses will bypass the back box giving more sound.
 
jonathancaddick1 said:
I've taken one of the foam bits out of the sound gen, I found that both out was a bit too much but might try again with the decat now.

Yes I'm in the UK, mine definitely had the secondary cats, I have them in my boot to put back on in the case of MOT failure.

Heres a short video of the sound from inside the cabin at different speeds etc, as you can hear not a massive change but better than OEM I think.

https://youtu.be/-yULBQm4IFI
Click to expand...
Both out is too much, however instead of putting a whole one back in cut one third of the remaining piece and put it back in leaving the other two thirds out, you should now have just one sixth of the origanal foam and should have a much meatier but not overboard sound in the cabin, give it a try, nowt to lose, you can always pop it back in if you don't like it, sounds awesome tho imo :thumbsup:
 
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