De-cat

[murphy1059]

hi,

i have recentley fitted a scorpian exhaust cat back system to my is,but i am after a de-cat pipe for it but i cant find one anywhere, i looked at an old forum topic saying that a dealer sold them on eBay but cant find them. so doest anyone know where to get one? my is is an 52 plate btw as i read that it matters to get the correct mach. cheers

[Dimitris Papamichail]

You can just go to an exhaust shop and fit a pipe in mate. You must have in mind that if you go for this option (decat) you must fit a wideband O2 sensor otherwise you will have the check engine light all the time. I thing Sparkystav is aslo selling his old decat pipe. he might still have it for sale.

[murphy1059]

You can just go to an exhaust shop and fit a pipe in mate. You must have in mind that if you go for this option (decat) you must fit a wideband O2 sensor otherwise you will have the check engine light all the time. I thing Sparkystav is aslo selling his old decat pipe. he might still have it for sale.

cheers 4 the info mate, but wish i read it yesterday as last night i managed to find one on the net(it has a hole pre drilled for the o2 sensor), bit woried if its going to fit or not but i will just have to wait and see,never fitted one before but hopefully it will be as easy (preferbly eaysier) than the system.lol,

any way thanks for the reply, and btw your is is amasing!

[Dimitris Papamichail]

I hope everything works ok mate

[Asi]

i think Stav has already sold his

[murphy1059]

i think Stav has already sold his

yeh i had a look for his but cudnt find it,(to compare the price lol) and yeh cheers il coment on here when it arives and say how it went.

[murphy1059]

You can just go to an exhaust shop and fit a pipe in mate. You must have in mind that if you go for this option (decat) you must fit a wideband O2 sensor otherwise you will have the check engine light all the time. I thing Sparkystav is aslo selling his old decat pipe. he might still have it for sale.

cr*p jst read an email saing that il have to wait till next month for it to come if i still want it, so think il pay a visit to an exhaust shop like you sugested.

[Asi]

a decent exhaust shop would be able to make one no problem

[flyeris]

You can just go to an exhaust shop and fit a pipe in mate. You must have in mind that if you go for this option (decat) you must fit a wideband O2 sensor otherwise you will have the check engine light all the time. I thing Sparkystav is aslo selling his old decat pipe. he might still have it for sale.

Does fitting a oxygen sensor spacer solve this problem? Has anybody tried putting such after going De-cat instead of changing the oxygen sensor?

eBay link: http://cgi.ebay.com/ebaymotors/ws/eBayISAP...em=290388574754

[Enright]

Is this the sort of thing that this topic is referring to?

http://cgi.ebay.co.uk/LEXUS-IS200-2-0-STAINLESS-STEEL-EXHAUST-DECAT-PIPE-/350371346962?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item5193c27a12

If so, please can anyone quote on their experiences with theirs? Specifically:

Can the car still pass an MOT with it fitted?

Did you need to change the O2 sensor? If so, how much did you have to spend on one and where did you get it from?

What difference in power/economy did it produce?

Alternatively, can you just remove the internals from the (edit: PRE-)cats for broadly the same result?

[fjcfarrar]

If so, please can anyone quote on their experiences with theirs? Specifically:

Can the car still pass an MOT with it fitted?

Did you need to change the O2 sensor? If so, how much did you have to spend on one and where did you get it from?

What difference in power/economy did it produce?

Alternatively, can you just remove the internals from the cats for broadly the same result?

I doubt there is an MOT tester slack enough to pass the car with no Cat. To detect any minimal improvement in performance produced by removing it; you will need to get a tattoo up your neck in an oriental language you don't understand and/or have a vivid imagination - although the car could be slightly louder while you drive around breaking the law by taking it out. People have successfully removed Cat elements using the same tools as used previously to remove their brains.

[Tango]

I doubt there is an MOT tester slack enough to pass the car with no Cat. To detect any minimal improvement in performance produced by removing it; you will need to get a tattoo up your neck in an oriental language you don't understand and/or have a vivid imagination - although the car could be slightly louder while you drive around breaking the law by taking it out. People have successfully removed Cat elements using the same tools as used previously to remove their brains.

Being a bit harsh on the lad , I'm sure when we were young and experimenting we did equally foolish and stupid things , but you learn from your mistakes, well those that don't kill you anyway.:eerrrmm:

[Enright]

I doubt there is an MOT tester slack enough to pass the car with no Cat. To detect any minimal improvement in performance produced by removing it; you will need to get a tattoo up your neck in an oriental language you don't understand and/or have a vivid imagination - although the car could be slightly louder while you drive around breaking the law by taking it out. People have successfully removed Cat elements using the same tools as used previously to remove their brains.

OK then, in that case can you recommend any good tattoo parlours please, because I’m obviously missing one! :P :winky:

I’ve already come at this from the opposite direction on my Elan, with stunning results:

It had a drink problem from before I bought it, averaging a truly awful 22mpg. As one of the early M100 SE’s it was only fitted with the standard open loop system. There was provision for an O2 sensor, pre-cat and catalytic converter for the export market, but being as these weren’t law in the UK until the introduction of new models after 1991, none of them needed to be fitted. Instead there was a bung where the O2 sensor could go, the pre-cat was hollow with no honeycomb inside, and the main exhaust system was mercifully un-strangled. This presented a great opportunity...

Installing a closed-loop (S2) Everest chip and an O2 sensor instantly corrected the stochiometric (air-fuel) ratio to 14.7:1 and as a result quartered the emissions. IIRC the CO limit for older cars without cats is 3.5%, and for those with them fitted as standard it is just 0.4%. Even without a pre-cat or main cat they came down to 0.65% - well inside the actual limit and only a whisker over a cat equipped car’s! This was on the MOT tester’s own machine, meaning that they were hardly going to argue with it, I didn’t have to rely on them being “slack”, and the car ended up completely legal.

Furthermore my fuel consumption increased by at least a third, and I’ve even seen in the 40’s on a run.

Then there was the power increase - the chip improved the boost pressure and fuelling, while the sensor ensured that the burn was as efficient as possible.

So I gained 40bhp, up from the original 165. Not bad for a 1.6, and living proof that you CAN have your cake and eat it!

Many fellow Elaners have since followed my lead and gone closed-loop with no adverse effects. See here:

http://forum.lotuselancentral.com/viewtopic.php?f=33&t=13359

Now back to my original question on the Lexus but with a few more details, as since my last post there’s been some daylight which has given me chance to look at the system a little more:

Most of the work has already been done in this case because the O2 sensor is fitted on the exhaust manifold just upstream of the pre-cats, and the main cat looks to be about level with the B-pillars.

So as expected the O2 sensor only measures the emissions as they come out of the engine, and passes the signal back to the ECU to alter the ignition/fuelling accordingly. Then the 2 pre-cats and the main cat simply scrub the spent gases to bring the CO level down by the last few tenths of a percent to below the legal limit.

There’s a very fancy looking exhaust manifold on eBay at the moment which does away with the pre-cats, and then as an alternative there’s the de-cat pipe which I previously linked to.

Increasing flow, as long as the air-fuel ratio stays correct, should be the first step in either releasing more power or upping fuel economy (or if you’re really lucky, both).

Past experience tells me that cars produced for the global market are built to be easily tailored to the strictest emissions standards on a regional basis, and ours aren’t the strictest by far. It comes down to how good the engine management system is in reducing emissions in the first place, before what’s left is passed through the exhaust system and ultimately measured.

I’d still like to know how hard the cats are forced to work, how good a job do they do, and why would getting rid of any of them produce an engine check-light when the gases have already passed the sensor? Could it be because the engine can now breathe properly due to the freer flowing air, so it has too little back-pressure?

Thanks in advance for any helpful replies! :D

[ormi]

as a mot tester yes a car can pass its mot with no cat it doesnt need one to pass as long as the emmissions are within the regs....

your car can even fail the emmissions with a cat....

fig 1 boy racer decatted car full exhaust check on the tester co 0.20 pass here you go mr boy racer a lovely bit of green paper for you

fig 2 middle aged boy clean standard car with cat checked on tester co 0.50 sorry pal a fail heres your red bit of paper....

cat not needed to pass mot as long as in pass specs

[fjcfarrar]

as a mot tester yes a car can pass its mot with no cat it doesnt need one to pass as long as the emmissions are within the regs....

your car can even fail the emmissions with a cat....

fig 1 boy racer decatted car full exhaust check on the tester co 0.20 pass here you go mr boy racer a lovely bit of green paper for you

fig 2 middle aged boy clean standard car with cat checked on tester co 0.50 sorry pal a fail heres your red bit of paper....

cat not needed to pass mot as long as in pass specs

The Law requires that vehicles manufactured after ?? (date I can't remember, but mid 90's) must be fitted with a Catalytic Convertor and if original equipment before that date must be maintained in effective condition. Perhaps you could describe an MOT tester as at least a bit slack if he didn't notice one was missing during the manadatory inspection.

It is well known that Cats can reduce efficiency because of flow restrictions etc, but by 1999 (first IS 200s) improved cat designs and better ECU control meant that any reduction is marginal - detectable with measuring equipment but not when driving - certainly not worth fitting an empty shell or risking failure at a properly conducted MOT.

Losses in the OEM Cat with high performance mods can become significant. The solution to comply with Law is to fit a Cat desigened for higher flow rates etc. - or alternatively Decat & no road use/an accomodating MOT Tester.

[ormi]

as a mot tester yes a car can pass its mot with no cat it doesnt need one to pass as long as the emmissions are within the regs....

your car can even fail the emmissions with a cat....

fig 1 boy racer decatted car full exhaust check on the tester co 0.20 pass here you go mr boy racer a lovely bit of green paper for you

fig 2 middle aged boy clean standard car with cat checked on tester co 0.50 sorry pal a fail heres your red bit of paper....

cat not needed to pass mot as long as in pass specs

The Law requires that vehicles manufactured after ?? (date I can't remember, but mid 90's) must be fitted with a Catalytic Convertor and if original equipment before that date must be maintained in effective condition. Perhaps you could describe an MOT tester as at least a bit slack if he didn't notice one was missing during the manadatory inspection.

It is well known that Cats can reduce efficiency because of flow restrictions etc, but by 1999 (first IS 200s) improved cat designs and better ECU control meant that any reduction is marginal - detectable with measuring equipment but not when driving - certainly not worth fitting an empty shell or risking failure at a properly conducted MOT.

Losses in the OEM Cat with high performance mods can become significant. The solution to comply with Law is to fit a Cat desigened for higher flow rates etc. - or alternatively Decat & no road use/an accomodating MOT Tester.

i am not saying its worth while removing the cat at most on a n/a car you wont even notice any gains!!!!!

and in no place in the MOT manual does it say check a cat is present!!!!!!no place at all!!! as most modern cars you cant see the cats for undertrays and you cant remove undertrays during an mot!yes you carry out a cat test but that doesnt involve checking its their it involves hooking it up to a gas meter...so if it passes a cat test with no cat(not all cars will) then thats that....visually checking the exhaust involves checking for blows missing rubbers bad corrosion no obstructions in the tail pipe as said above on most new cars you cant see the cat(new yaris,new avensis,vauxhall vx220,lotus,new mercs,bmw's to name a few oh and poss your isf)if it passes the emmissions their is no place to fail it for not having a cat(as in no option on the mot computer)..... i beg your pardon a properly conducted mot.........i work for a main dealer and take pride in what i do and im good at what i do so every mot/service/repair is properly conducted thank you very much!!

many members on here will tell you that as well.....

[ormi]

The M.O.T. Inspection Manual Issue Date 06 June 2010 Information Method of Inspection Reason for Rejection D. Full CAT Test When to do the test It is recommended that the extended test is carried out as soon as possible after the BET Test. This allows the test to be carried out on a fully warmed up engine. Printouts The 1996 specification analysers will produce two printouts. One printout must be retained by the VTS for a period of three months. The other printout must be made available to the vehicle presenter. Cosmetic engine covers Where engine speed can only be measured by the removal of a cosmetic engine cover, the engine speed must be measured if the cover can be easily un-clipped. Otherwise, engine speed measurement may be by-passed. Engine speed and engine oil temperature must be measured whenever possible. If engine speed cannot be measured then the vehicle tachometer should be used if fitted. Otherwise, a subjective estimate should be made. Where, in exceptional circumstances, the engine oil temperature cannot be measured (eg in the case of a dry sump engine), check one of the following: temperature gauge showed warm engine, cooling fan had cut in or coolant pipes were hot. 1. A suitable exhaust gas analyser will be needed to perform this inspection. Check that the analyser probe can be inserted into the tailpipe 2. a. Ensure that the analyser’s daily leak check has been performed b. identify the vehicle specific test limits using the flow charts c. connect the engine speed measuring device and insert the engine oil temperature measuring probe into the dipstick hole d. engine pre-conditioning: Check the engine oil temperature. If it is below the minimum vehicle specific requirement, raise the engine speed to between 2000rpm and 3000rpm and maintain this speed until the minimum engine oil temperature has been reached. Remove temperature measuring probe and replace dipstick e. perform a HC hang-up check and ensure that HC<20ppm before continuing. Insert the analyser sample probe f. 1st Fast Idle Test: Raise the engine speed to the vehicle specific fast idle speed and maintain for 30 seconds. If the engine speed drifts outside the fast idle speed range, begin the 30 second countdown again. During the last 5 seconds note the readings for CO, HC and lambda, and record the results 1. The emissions cannot be measured because a tailpipe accessory is fitted which prevents insertion of the analyser probe. 2. a. The engine idle speed is clearly above the vehicle specific limit. Note: If the engine speed is clearly above the vehicle specific limit and this can be easily adjusted, a tester may perform the adjustment and complete the test - the adjustment is not, however, part of the MOT test. b. In the 2nd fast idle test, one or more of the following exceeds the vehicle specific or default limits continuously for the last 5 seconds of the 30 second countdown: · Carbon monoxide (CO) · Hydrocarbons (HC) · Lambda (l) c. In the idle test, the following gas exceeds the vehicle specific or default limit continuously for the last 5 seconds of the 30 second countdown · Carbon monoxide (CO). Cont’d

The M.O.T. Inspection Manual Issue Date 06 June 2010 Method of Inspection g. if the vehicle has passed the first fast idle test, then go to paragraph (j), otherwise go to paragraph (h) h. additional engine pre-conditioning: Run the engine between 2000- 3000rpm for 3 minutes or until all the emissions are within limits. If the engine speed goes outside the fast idle range, then freeze the countdown until the engine speed is within range once again i. 2nd Fast Idle Test: Repeat the procedure as laid down in paragraph (f), then go to paragraph (j) j. catalyst stabilisation: Raise the engine speed to the vehicle specific fast idle speed and maintain for 30 seconds. If the engine speed drifts outside the fast idle speed range then begin the 30 second countdown again k. idle test: Allow the engine to idle during a 30 second countdown. During the last 5 seconds, note the CO reading and record the result l. Remove analyser sample probe and engine speed measuring device. 7.3 Exhaust Emissions - Spark Ignition - CAT Test

their you go the full mot guide on emissions testing note at no point does it say check for a cat...

if you would like the one for the guide lines on checking the exhaust i'll put that up too??

[fjcfarrar]

The M.O.T. Inspection Manual Issue Date 06 June 2010.... Detailed description of emmision tests followed......

their you go the full mot guide on emissions testing note at no point does it say check for a cat...

if you would like the one for the guide lines on checking the exhaust i'll put that up too??

The presence of a Cat is part of the over-riding Condition & Use Regulations where a failure would possibly mean the emission test would not even be carried out because the car could be considered as unfit for the MOT to procede. Do you imagine that when Legislation insisted that Cats were mandatorily fitted by ALL manufacturers to ALL cars, that any Tom, Di*k or Harry could take them off if they felt like it - just because many cars without Cats could pass standard emission tests? Given that, who other than the MOT tester is going to police it?

A Cat is part of the basic essential requirements for cars - just like windscreens without significant damage or tints, airbags, functional speedos etc. but more environmental in nature than safety-related. The Cat is supposed to take care of conditions outside the scope of limited emission tests possible at the MOT.

Agreed a removed Cat may not always be obvious, but when it is, deliberately ignoring it is taking a tester's discretion a bit far. It is just this sort of issue that makes the MOT Tester's job much more complex and difficult than it appears with a minefield of seemingly conflicting legislation.

I'm not going to take this any further except to say that keeping a Cat ensures remaining within the law (assuming emissions etc. are also OK): removing it is at least questionable. Is it worth the risk? If you want a definitive answer, write to VOSA with a direct question about the legality of using a car with the Cat removed.

[The Transporter]

Provided that the emissions are within the required tolerances prescribed for the year of vehicle, then it is irrelavent wheater a cat is there or not... I would say that virtually all correctly adjusted modern fuel injected petrol enginse would meet the requirements without a cat.... Or in the words of my old but very experienced Motor vehicle technology lecturer... With the control that you get from a modern engine managemet system, you don't need a B+@@?y catalytic converter.

Having said that, I doubt that the gains of removing it from an IS200 will be great or even noticable... If you want to go fast, then start with a fast car.

[Enright]

Fortunately I did. But then I bought a Lexus!

Going back to my earlier post, for me it was as much (if not more) about eeking out a bit better economy through improved flow. After all, it's usually a trade-off - it doesn't HAVE to be all about power. Besides, I have the Lotus for flies in the eyes motoring. My IS200 just needs to move me around in comfort - preferably without drinkiing the contents of my wallet!

I do get the feeling though that the IS's engine is a but gutless for it's size, so because it has to work harder that contributes to the poor mpg. Being partially strangled could account for only achiving 155bhp from 2 litres.

It's a shame that nobody replied to my original questions who had actually bought and used the parts. Maybe that means it's all just been a big marketting exercise and they haven't actually sold any!!!

[Koko]

You can just go to an exhaust shop and fit a pipe in mate. You must have in mind that if you go for this option (decat) you must fit a wideband O2 sensor otherwise you will have the check engine light all the time. I thing Sparkystav is aslo selling his old decat pipe. he might still have it for sale.

Hi,

Need your help Ive got a decat system on mine since this summer and the check engine light came on a couple of days ago. Took her to my local dealer and the code is for the O2 sensor. Would be good to know what to do and where can I get this wideband 02 sensor from. Googled it and there is many of these and I dont know which one is good for me. Hope you can help

Regards

[ormi]

The M.O.T. Inspection Manual Issue Date 06 June 2010.... Detailed description of emmision tests followed......

their you go the full mot guide on emissions testing note at no point does it say check for a cat...

if you would like the one for the guide lines on checking the exhaust i'll put that up too??

The presence of a Cat is part of the over-riding Condition & Use Regulations where a failure would possibly mean the emission test would not even be carried out because the car could be considered as unfit for the MOT to procede. Do you imagine that when Legislation insisted that Cats were mandatorily fitted by ALL manufacturers to ALL cars, that any Tom, Di*k or Harry could take them off if they felt like it - just because many cars without Cats could pass standard emission tests? Given that, who other than the MOT tester is going to police it?

A Cat is part of the basic essential requirements for cars - just like windscreens without significant damage or tints, airbags, functional speedos etc. but more environmental in nature than safety-related. The Cat is supposed to take care of conditions outside the scope of limited emission tests possible at the MOT.

Agreed a removed Cat may not always be obvious, but when it is, deliberately ignoring it is taking a tester's discretion a bit far. It is just this sort of issue that makes the MOT Tester's job much more complex and difficult than it appears with a minefield of seemingly conflicting legislation.

I'm not going to take this any further except to say that keeping a Cat ensures remaining within the law (assuming emissions etc. are also OK): removing it is at least questionable. Is it worth the risk? If you want a definitive answer, write to VOSA with a direct question about the legality of using a car with the Cat removed.

i have asked the boy that comes round to check us from vosa(phoned him today just to put my mind at ease) his answer if it passes the emissions you have no need to check the cats their if it fails thats when you end up looking but even then it doesnt fail on the cat missing(as said no option on the computer for this)it fails on the readings them selfs......

as i have said i see no point in removing the cat as modern cats arent too restrictive and any gains you will not even notice but condeming it to be illegal it wrong also as i have said only some cars will get through the emissions with the cat off......

[fjcfarrar]

The M.O.T. Inspection Manual Issue Date 06 June 2010.... Detailed description of emmision tests followed......

their you go the full mot guide on emissions testing note at no point does it say check for a cat...

if you would like the one for the guide lines on checking the exhaust i'll put that up too??

The presence of a Cat is part of the over-riding Condition & Use Regulations where a failure would possibly mean the emission test would not even be carried out because the car could be considered as unfit for the MOT to procede. Do you imagine that when Legislation insisted that Cats were mandatorily fitted by ALL manufacturers to ALL cars, that any Tom, Di*k or Harry could take them off if they felt like it - just because many cars without Cats could pass standard emission tests? Given that, who other than the MOT tester is going to police it?

A Cat is part of the basic essential requirements for cars - just like windscreens without significant damage or tints, airbags, functional speedos etc. but more environmental in nature than safety-related. The Cat is supposed to take care of conditions outside the scope of limited emission tests possible at the MOT.

Agreed a removed Cat may not always be obvious, but when it is, deliberately ignoring it is taking a tester's discretion a bit far. It is just this sort of issue that makes the MOT Tester's job much more complex and difficult than it appears with a minefield of seemingly conflicting legislation.

I'm not going to take this any further except to say that keeping a Cat ensures remaining within the law (assuming emissions etc. are also OK): removing it is at least questionable. Is it worth the risk? If you want a definitive answer, write to VOSA with a direct question about the legality of using a car with the Cat removed.

i have asked the boy that comes round to check us from vosa(phoned him today just to put my mind at ease) his answer if it passes the emissions you have no need to check the cats their if it fails thats when you end up looking but even then it doesnt fail on the cat missing(as said no option on the computer for this)it fails on the readings them selfs......

as i have said i see no point in removing the cat as modern cats arent too restrictive and any gains you will not even notice but condeming it to be illegal it wrong also as i have said only some cars will get through the emissions with the cat off......

I wasn't going to take this further but 1993 - 2009: Catalytic Convertors fitted MUST be replaced with suitable types. From 13 Aug 2009, on cars produced after 1st March 2001, Catalytic Converters can ONLY be replaced by type-approved versions of the original converter. I know it is a bit pickey, but neither includes getting rid of them with fines up to £5000 for doing so.

[ormi]

The M.O.T. Inspection Manual Issue Date 06 June 2010.... Detailed description of emmision tests followed......

their you go the full mot guide on emissions testing note at no point does it say check for a cat...

if you would like the one for the guide lines on checking the exhaust i'll put that up too??

The presence of a Cat is part of the over-riding Condition & Use Regulations where a failure would possibly mean the emission test would not even be carried out because the car could be considered as unfit for the MOT to procede. Do you imagine that when Legislation insisted that Cats were mandatorily fitted by ALL manufacturers to ALL cars, that any Tom, Di*k or Harry could take them off if they felt like it - just because many cars without Cats could pass standard emission tests? Given that, who other than the MOT tester is going to police it?

A Cat is part of the basic essential requirements for cars - just like windscreens without significant damage or tints, airbags, functional speedos etc. but more environmental in nature than safety-related. The Cat is supposed to take care of conditions outside the scope of limited emission tests possible at the MOT.

Agreed a removed Cat may not always be obvious, but when it is, deliberately ignoring it is taking a tester's discretion a bit far. It is just this sort of issue that makes the MOT Tester's job much more complex and difficult than it appears with a minefield of seemingly conflicting legislation.

I'm not going to take this any further except to say that keeping a Cat ensures remaining within the law (assuming emissions etc. are also OK): removing it is at least questionable. Is it worth the risk? If you want a definitive answer, write to VOSA with a direct question about the legality of using a car with the Cat removed.

i have asked the boy that comes round to check us from vosa(phoned him today just to put my mind at ease) his answer if it passes the emissions you have no need to check the cats their if it fails thats when you end up looking but even then it doesnt fail on the cat missing(as said no option on the computer for this)it fails on the readings them selfs......

as i have said i see no point in removing the cat as modern cats arent too restrictive and any gains you will not even notice but condeming it to be illegal it wrong also as i have said only some cars will get through the emissions with the cat off......

I wasn't going to take this further but 1993 - 2009: Catalytic Convertors fitted MUST be replaced with suitable types. From 13 Aug 2009, on cars produced after 1st March 2001, Catalytic Converters can ONLY be replaced by type-approved versions of the original converter. I know it is a bit pickey, but neither includes getting rid of them with fines up to £5000 for doing so.

weres this from?not the mot check list anyway?mibbi construction and use?in which case im not interested,i got involved due to people saying it will fail the mot which i have proved by posting up the emissions procedure that it wouldnt(as long as the emissions meet the standards set)and as said if you want i can post the exhaust one too....

if you did get a road side vosa check with the emissions and they were fine they wouldnt do you for no cat as your emissions are fine.

i run a tuned car the only things i have removed is the pre cats as they break up due to the charger(well the heat produced)so i have a prolex manifold but i am still runing the standard cat and dont have any plans to remove it...