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[Zippy2012]

Ive got a 3.0 v6 estate & both cats are original & seems like 1 is rattling slightly....

Does the car have to run 2 cats??

a mate is going to make me a pair of stainless manifolds & 3" system but i was wondering if i find a single cat off another 3.0ltr car on a single pipe system (i.e Bmw 535i) can i run a 2 into 1 from manifolds single cat & 3"bore pipe threw car to a single 3" in duel 2" out deflection box with 2x2.5" tailpipes...??

i know someone will say that manifactured system from factory will be best... but the cats are £100+ each side...
& as soon as a car enters a breakers thats the 1st things they remove with airsaw/oxy!
i dont want system to be too free flow as i know fueling mpg will be lost etc

but mainly will a single cat pass an mot?? 

[Kevin Wood]

Whatever cat you have, all the exhaust gases must flow through it for an MOT pass, so you can't just remove one from one bank.

A single V6 cat would probably be horribly restrictive if trying to flow the gases from both banks, so yes, you would need to find a cat from a similarly powered car. The cat also needs to be reasonably close to the exhaust manifold to ensure that the exhaust gases are hot enough to activate it.

So.. yes, there's no reason why it needs to be 2 cats but you'd have your work cut out to make a successful single cat system. You'd still need 2 lambda sensors, one in each banks' downpipe.

[Zippy2012]

Whatever cat you have, all the exhaust gases must flow through it for an MOT pass, so you can't just remove one from one bank.

A single V6 cat would probably be horribly restrictive if trying to flow the gases from both banks, so yes, you would need to find a cat from a similarly powered car. The cat also needs to be reasonably close to the exhaust manifold to ensure that the exhaust gases are hot enough to activate it.

So.. yes, there's no reason why it needs to be 2 cats but you'd have your work cut out to make a successful single cat system. You'd still need 2 lambda sensors, one in each banks' downpipe.

Looking under car i can poss fit a single cat relitivly in same place under car as the 2 already on there "hopefully" im hoping a good bmw 530i/535i straight 6 cat shud do the job...

is it just my car....? or do both the cats/center boxes sit slightly lower than the sills looking under car??

As every dam speed hump i seem to ground them across!! i.e 2/3 humps across road & the long single humps...?? all the rubbers are new & all fitted correctly?? thats why im thinking of bining them all for a single pipe system closer to underside of car...

ok my car is approx 30mm lower than a standard elite cdx cd gls but i never grounded out my cdx saloon on 30mm irmscher springs this much 8 years ago or are speed humps just getting bigger & brakeover angles more abrupt? & not really very good for a long car???

[Stallion]

getting rid of 2 centre boxes would make it alot louder matey! 

[Lazydocker]

Something to bear in mind though, all single pipe systems I/we have experienced on here have resulted in a loss of power... A slight "flatness" that was hard to pin point, just there

I'd be looking to keep a twin pipe system as designed, but in stainless

[geoffr70]

Whatever cat you have, all the exhaust gases must flow through it for an MOT pass, so you can't just remove one from one bank.

A single V6 cat would probably be horribly restrictive if trying to flow the gases from both banks, so yes, you would need to find a cat from a similarly powered car. The cat also needs to be reasonably close to the exhaust manifold to ensure that the exhaust gases are hot enough to activate it.

So.. yes, there's no reason why it needs to be 2 cats but you'd have your work cut out to make a successful single cat system. You'd still need 2 lambda sensors, one in each banks' downpipe.

Looking under car i can poss fit a single cat relitivly in same place under car as the 2 already on there "hopefully" im hoping a good bmw 530i/535i straight 6 cat shud do the job...

is it just my car....? or do both the cats/center boxes sit slightly lower than the sills looking under car??
As every dam speed hump i seem to ground them across!! i.e 2/3 humps across road & the long single humps...?? all the rubbers are new & all fitted correctly?? thats why im thinking of bining them all for a single pipe system closer to underside of car...

ok my car is approx 30mm lower than a standard elite cdx cd gls but i never grounded out my cdx saloon on 30mm irmscher springs this much 8 years ago or are speed humps just getting bigger & brakeover angles more abrupt? & not really very good for a long car???

I think it's all of them, at least 2.5s and 3.0s anyway. Never seen a DBW up close. My two are the same. Makes me nervous, especially now that cat converters are being nicked off parked cars! Bastaaaards.

Oh yeah Sprinter vans across the land are being targeted for this, must have good cats.

[Zippy2012]

getting rid of 2 centre boxes would make it alot louder matey! 

I did that on my last cdx 2.5 yeah louder but felt slower & didnt it use some fuel!!

so this time ive just removed the rear box & fitted 2x 2.5" stainless pipes with baffle plates (1 above & 1 below but 2" apart) to quieten it down for motorway use but still sounds awesome tho & with k&n panel filter & modifyed airbox sounds great from both ends!! & mpg is nearly the same!!

[ngrainqey]

if you want a cat good enough then your looking at something that'd have been 1k new, my dads old 3.8 camaro cat went (high flow single one as standard) and it was £1200ish for just the cat but it was good enough for both banks worth of exhaust gases

[Zippy2012]

if you want a cat good enough then your looking at something that'd have been 1k new, my dads old 3.8 camaro cat went (high flow single one as standard) and it was £1200ish for just the cat but it was good enough for both banks worth of exhaust gases

ive found on e bay some universal sport (freeflow 200cell) cats for £79 each but are staggered so will sit higher up & wont ground out etc so i may keep the duel system but make it 3" stainless threw car & a decent tail box or pair of center deflection boxes or a single 2x3" in & 2x3" exit...