Not joined yet? Register for free and enjoy features such as alerts, private messaging and viewing latest posts and topics.

Questions on decatting UK!

2003 - 2009, roadster, coupe, facelift
Post Reply
Lukie761
Newbie
Newbie
Posts: 25
Joined: Wed Dec 28, 2016 9:33 pm

Questions on decatting UK!

Post by Lukie761 » Sun Apr 23, 2017 10:16 pm

Hi guys,

I'm very excited to be having a custom exhaust system made and fitted this coming Saturday, however I have some questions that I really need answering to make my decisions...
1.UK exhaust spec, are there cats in both the manifold and under the car?
2.if so, does removal of the cats under the car give mot failure.
3.what set-ups have you guys done? Anyone gone decat straight through to backbox? Thoughts on it?

I'm really stuck guys, I think decat straight through to backbox would be awesome, I just need to know the potential issues and almost have some clarity.

Any helpful answers are greatly appreciated!!

Luke
BMW Z4 3.0si 2008 Coupé. M sport: steering wheel, suspension, alloys, seats.
Sat nav, cruise, automatic. :fuelfire:

RyanB88
Member
Member
Posts: 436
Joined: Sun Apr 09, 2017 6:51 pm

Questions on decatting UK!

Post by RyanB88 » Sun Apr 23, 2017 10:27 pm

You can remove the secondary cat and still pass the MOT but not the primrary one
Z4 now sold :(

Current - M235i :thumbsup:

Lukie761
Newbie
Newbie
Posts: 25
Joined: Wed Dec 28, 2016 9:33 pm

Questions on decatting UK!

Post by Lukie761 » Sun Apr 23, 2017 10:31 pm

Cheers ryan, don't they do a visual inspection for cats however?
BMW Z4 3.0si 2008 Coupé. M sport: steering wheel, suspension, alloys, seats.
Sat nav, cruise, automatic. :fuelfire:

Mister T
Senior Member
Senior Member
Posts: 1073
Joined: Sun Oct 12, 2014 2:18 am

Questions on decatting UK!

Post by Mister T » Sun Apr 23, 2017 10:39 pm

There's no visual inspection for the cat, it just comes down to the emissions test

Lukie761
Newbie
Newbie
Posts: 25
Joined: Wed Dec 28, 2016 9:33 pm

Questions on decatting UK!

Post by Lukie761 » Sun Apr 23, 2017 10:44 pm

Thank you guys, and does anyone know if there's any sort of popping/cracking with the secondaries deleted?
BMW Z4 3.0si 2008 Coupé. M sport: steering wheel, suspension, alloys, seats.
Sat nav, cruise, automatic. :fuelfire:

RyanB88
Member
Member
Posts: 436
Joined: Sun Apr 09, 2017 6:51 pm

Questions on decatting UK!

Post by RyanB88 » Sun Apr 23, 2017 10:45 pm

Lukie761 wrote: Sun Apr 23, 2017 10:31 pm Cheers ryan, don't they do a visual inspection for cats however?

There is a visual inspection for the secondary cat, the primrary is down to the emissions test which it won't pass if removed!
Z4 now sold :(

Current - M235i :thumbsup:

RyanB88
Member
Member
Posts: 436
Joined: Sun Apr 09, 2017 6:51 pm

Questions on decatting UK!

Post by RyanB88 » Sun Apr 23, 2017 10:46 pm

Lukie761 wrote: Sun Apr 23, 2017 10:44 pm Thank you guys, and does anyone know if there's any sort of popping/cracking with the secondaries deleted?

Search for "ducklakeview" on here, vids in his threads :)
Z4 now sold :(

Current - M235i :thumbsup:

Marius
Senior Member
Senior Member
Posts: 1775
Joined: Sun Aug 12, 2012 12:01 pm
Location: west sussex
Contact:

Questions on decatting UK!

Post by Marius » Mon Apr 24, 2017 6:51 am

Give extra £20 to MOT Tester and it will pass witout any cats :rofl:

Nautrey
Newbie
Newbie
Posts: 36
Joined: Thu Jul 07, 2016 8:56 pm

Questions on decatting UK!

Post by Nautrey » Sun Jun 11, 2017 7:47 pm

I was just looking into decats. Does anyone know if there is a bolt on kit or is it just a matter of getting one fabricated?
E85 Sterling Grey 3.0l :driving:

User avatar
Ducklakeview
Lifer
Lifer
Posts: 6362
Joined: Tue Mar 22, 2016 4:08 pm
Location: Merseyside

Questions on decatting UK!

Post by Ducklakeview » Sun Jun 11, 2017 8:11 pm

Nautrey wrote: Sun Jun 11, 2017 7:47 pm I was just looking into decats. Does anyone know if there is a bolt on kit or is it just a matter of getting one fabricated?
The way I have done mine is by removing from the car, carefully removing the heatshield and then opening up the cat with the plasma. I then gutted them before welding up and replacing the heatshield. As a result, my car looks standard underneath and no problems with the mot. As mentioned, if the cats are visibly missing, it is a fail.

Mine pops and crackles like a good'un now though 😃 It also feels like it's been remapped, the increase in power and throttle response is THAT noticeable.

Mike

User avatar
Ewazix
Lifer
Lifer
Posts: 4721
Joined: Sun May 02, 2010 5:30 pm
Location: Somerset

Questions on decatting UK!

Post by Ewazix » Sun Jun 11, 2017 8:58 pm

As a matter of interest re the above advice that removal of the secondary Cat is not an MOT fail in itself, the MOT test manual for petrol engined cars first used after 2002 and listed in the database (which the Z4 is) seems to say it should be a fail,

"Reason for rejection 3. A catalytic converter or particulate filter missing where one was fitted as standard "

https://www.mot-testing.service.gov.uk/ ... 000101.htm

https://www.mot-testing.service.gov.uk/ ... 000311.htm

Whether you can get away with it is a different question but it looks like it should be fail, unless I'm reading it wrong? :?
2003 2.5 SE, low miles, Sterling Grey, 108's & Eagles, no stubby here! Unmolested.
2018 Cooper S Countryman
Fiesta Ecoboost

User avatar
Newbers
Member
Member
Posts: 569
Joined: Sat Jun 12, 2010 12:10 pm
Location: St Albans (one days march from London)

Questions on decatting UK!

Post by Newbers » Mon Jun 12, 2017 10:12 am

Has anyone dyno tested before/after (or even a timed 0 - 60) with this rather appealing cat gutting exercise?
Coupe, KW coil overs, PSB limiters, Powerflex ARB bushes, 18" CSL reps, Aero skirts, ZHP leather knob, Whippy and proud. Probably needs a wash :roll:

User avatar
MACK
Lifer
Lifer
Posts: 3600
Joined: Mon Jun 15, 2015 11:38 am
Location: Manchester

Questions on decatting UK!

Post by MACK » Mon Jun 12, 2017 10:28 am

Ducklakeview wrote: Sun Jun 11, 2017 8:11 pm
Nautrey wrote: Sun Jun 11, 2017 7:47 pm I was just looking into decats. Does anyone know if there is a bolt on kit or is it just a matter of getting one fabricated?
The way I have done mine is by removing from the car, carefully removing the heatshield and then opening up the cat with the plasma. I then gutted them before welding up and replacing the heatshield. As a result, my car looks standard underneath and no problems with the mot. As mentioned, if the cats are visibly missing, it is a fail.

Mine pops and crackles like a good'un now though 😃 It also feels like it's been remapped, the increase in power and throttle response is THAT noticeable.

Mike
Mike have you thought about gutting the cat then welding a pipe between the two opening, (so its like a straight through exhaust pipe) rather than just leaving the Cat shell as an empty box with the exhaust gases going into it. If noise is an issue I suppose you could even add some exhaust silencer wadding around the new pipe inside the gutted cat casing to quieten things down.

Could be your next "line" to add to the list of other products
Silver 05 3.0i SE
Mods inc - F/L Xenons Clear Ind Rear Lights M Sport Seats & Wheel Eibach/B4 3.64 DIFF (SOLD)

White E89 20i M Sport
Mods inc- B12 kit, M3 Arms, 18" Zito 935's with PS4's, Decat & Remap, Switchable Exhaust Flap (SOLD)

User avatar
Ducklakeview
Lifer
Lifer
Posts: 6362
Joined: Tue Mar 22, 2016 4:08 pm
Location: Merseyside

Questions on decatting UK!

Post by Ducklakeview » Mon Jun 12, 2017 11:47 am

MACK wrote: Mon Jun 12, 2017 10:28 am
Ducklakeview wrote: Sun Jun 11, 2017 8:11 pm
Nautrey wrote: Sun Jun 11, 2017 7:47 pm I was just looking into decats. Does anyone know if there is a bolt on kit or is it just a matter of getting one fabricated?
The way I have done mine is by removing from the car, carefully removing the heatshield and then opening up the cat with the plasma. I then gutted them before welding up and replacing the heatshield. As a result, my car looks standard underneath and no problems with the mot. As mentioned, if the cats are visibly missing, it is a fail.

Mine pops and crackles like a good'un now though 😃 It also feels like it's been remapped, the increase in power and throttle response is THAT noticeable.

Mike
Mike have you thought about gutting the cat then welding a pipe between the two opening, (so its like a straight through exhaust pipe) rather than just leaving the Cat shell as an empty box with the exhaust gases going into it. If noise is an issue I suppose you could even add some exhaust silencer wadding around the new pipe inside the gutted cat casing to quieten things down.

Could be your next "line" to add to the list of other products
Nooo... I LOVE the noise it makes now!!

Mike

Post Reply