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So now im the proud owner (if the sale goes through of course) of some 100 Cell Milly sports cats ... rather impulsive purchase ... really shoud have asked the question beforehand! But ... will a remap be essential?

It's currently running a BMC filter and non res non valved Milly .... so should sound spectacular!!

I guess really the question is ... what are the implications of not having a remap and running the full system? (oh ... and i didn't remap when the cat back went on either)

Yes.

Ok .... so essential .. as in it wont drive properly or cause damage?

Not trying to be a cheapsake but TBH im not seriously fussed about the performace ... and 500+ bucks is alot for a piece of software ....

don't get me wrong ... if i need one obviously ill get it done ... just curious to the implications of avoiding it.

yes pretty sure you will need a remap, only because as there as there are no precats on these you will likkely need to get a cat delete map as the 02 sensors will throw up codes right away (if there is even anywhere in the 100 cell cat to put the original upstream wideband sensor into) as i only see 2 holes and i think there are 3 sensors on the RS , one wideband sensor above the precat and one above the main cat and one below the main cat (to check the final exiting exhaust cas to ensure main cat is working)
maybe a call to millltek to clarify ?

Essential to avoid error codes (especially with 100 cell) but well worth it...

So doing a bit of research and ... well a remap will obviously be the best option but the cost ...cira 550 quid + IMO is alot of money for someone in my situation (just wanting the full milltek system to work without throwing CEL codes 24/7)

So it seems it all comes down to the 4 Oxygen (O2) sensors, otherwise called Lambda sensors. Two of which are located in either exhaust pipe (one for either bank of cylinders) before the pre cats and determine the amount of oxygen present in the gas emitted by the engine as a product of combustion. In the full milltek system these O2 sensors will remain in this postion (between the exhaust manifold and cat) and so the fitting of race cats will not affect the reading. According to the Ross Tech website these first two sensors allow the engine to adjust the 'trim' settings which in effect allow the engine to 'learn' the correct mix of fuel and air within the cylinders in any given situation (idle/full load etc) to provide the optimum combustion conditions.

The second set of O2 sensors are the ones that seem to cause the hassle. In the OE exhaust system they are located between the pre cat and main cat. In the Milltek system they are located after the single 100 cell cat. From what i can work out, in the OE system they measure the amount of oxygen in the exhaust gases after they have passed through the pre cat. They don't affect the 'trim' settings and therefore dont adjust the A/F ratio. (please correct me if im wrong on this though). So their main/only purpose is to ensure that the cats are functioning correctly.

IF this is the case then the fitting of race cats (without a remap) will cause the O2 readings in these second set of O2 sensors to alter from the readings when fitted in the OE system. This disparity in readings will make the ECU 'think' that the cats are not functioning correctly (because you haven't used a Remap to 'tell' it that you've fitted race cats) and therefore thrown a CEL.

Again IF this is correct the CEL is in effect harmless as it relates to an issue that isnt actually an issue. Therefore the fitting of race cats will NOT affect the A/F ratio and cause the engine to run overly lean or rich. I know there will be other consequences caused by fitting the race cats without a remap(such as reduced back pressure) but they will only adversely affect performance slightly.

I did also read on one site that remaps such as the REVO one actually switch off the ability of a reading from these second set of O2 sensors to cause a CEL. How true this is ... i have no idea!

Now, apparently to overcome these 'harmless' CEL's you can buy an O2 spacer (sometimes people use spark plug de fowlers... i think theyre only availabe in the states though) like this one ...

http://www.awesome-gti.co.uk/product.php?xProd=32887

They mechnically distance the second set of O2 sensors from the post cat exhaust gas flow and so in essence allow the sensor to measure O2 readings similar to those seen in an OE exhaust system and therefore no CEL. A bit heath robinson but apparently they work.

Sooooo .... has anyone actually used these or have any info on the implication of their use (im sure its not as simplistic as it reads above). I did speak to a respected remapping company eariler today and they did confirm that fitting race cats without a remap would not cause the engine to run dangerously lean but didn't go into any specifics ... something to do with wideband O2 sensors??

Im i need a remap i need a remap ... ill just have to save up before fitting the cats but if there is no REAL reason to spend many pounds ATM then i'll wait till the CAF and polish and port is carried out till i get a remap

you dont have to have a remap but the car will benifit from it,

however if you fit spacers to the second set of lambda sensors all will be fine,

i wouldnt but those ones at 30 quid a pop tho, these below will work fine

http://www.ebay.co.uk/itm/O2-Oxygen-lam ... 3a6d50bcc7

curious to why you bought the race cats if your not bothered about performance? fuel consumption will go up too.

I just love the sound ... I would have brought de-cats but too much of a PITA come MOT time ... so anything that unleashes that V8 I'm up for

I wouldn't say not bothered about performance but I don't really have the extra cash ATM for a map so if I can postpone it till I get the other mods done it will help alot! ...

Oh, and thanks for the link ... They look very similar to the 'spark plug defowlers'

It wont even take a few hundred miles before warning lights are on,it will run like a bag o sh*te from cold until fully warm,the std pre cats warm up v quickly and mixture is adjusted accordingly,systems are worth nothing really powerwise and highflow cats you will only get half the benefit in terms of power until properly mapped,1st pair of lambdas are deleted when mapped,i noticed the difference especially in the midrange after just fitting the system and cats but same again after mapping etc and it ran nicely from cold,well as nice as they do from cold!

With 100cels it will be a LOT louder than just cat back non-res .

I had mine remapped at the same time as i had 100cels fitted so no idea how bad it runs without one.

J

Ordered those eBay O2 spacers and the cats are being shipped tomorrow. So come early next week I'll find out ... vVV excited ... maybe too much!

soundclips or you just have a saxo

So .... Cats arrived (finally!) and so did the O2 spacers .... Got the car up on ramps this morning in an attempt to fit 'em.

What a BUGGER! ... two of the cat - manifold bolts are easy to get to but the third one seems almost impossible. Its right up behind the pipe. In addition, the rest of the exhaust will have to come off to allow the cats to slide far enough back to remove. Maybe with the cat back section removed the cats can be tilted downward to access the awkward third bolt .... but with the snow falling and hands begining to freeze i had to admit defeat and call it a day

Any pointers welcome!! ... i HATE losing .. so am very reluctant to call in the pros!

The other option is a 'mil eliminator' - essentially just a suitable resistor inline on the post o2 sensor. The ecu is just looking for a difference between the two sensors which the resistor simulates nicely.