Is it possible to delete the first cat on stock DP

[Ranton]

a way to remove the first Catalic Converter from the factory Downpipe and leave the second one in.. without having to go to a oversize downpipe?

I like having a stock size down pipe.. i know on VXR AStras etx most people remove the first cat and leave the second..

i dont like the restriction being that close to the turbs

[PaulG]

pretty sure it will mess with your o2 sensors n such... throw CEL's and generly do bad things...

i have removed the second one with no worries at all... minimal gains..

[Ranton]

you would relocate the sensors after doing so....

what im thinking is if possible.. than cut the first one.. and replace the second one with a hiflo

[kagerou]

isn't the second o2 sensor behind the second cat in the factory system? i dont remember unfortunately

but with all the aftermarket exhausts, the second o2 sensor is behind the cat, which is relocated to approximately where the second cat is positioned in the factory system, so i dont really see a problem with punching out the first cat, you'll just get a higher reading on the second o2 sensor

if you can get the labour done cheap, then it would be worth trying considering the cost of an aftermarket downpipe

[2XS]

You can remove the first DP cat, but you need to relocate the O2 from in front of the 2nd cat to after.

[2000MNLESS]

^^ No you don't .... Never did on mine. Threw 2-3 emission CEL's then was fine after that.

[Nuliaj]

Why waste time and money trying to remove the first cat (gotta remove the DP to do it) and rewire, when you can easily just cut the second cat out from under the car for a fraction of the cost. Regardless of which one you remove, there's not going to be much difference between the two, certainly not enough to justify the difference in cost.

[Street Road Laino]

^^ No you don't .... Never did on mine. Threw 2-3 emission CEL's then was fine after that.

isnt the sensor on the turboxs out of the pipe anyway

[2000MNLESS]

isnt the sensor on the turboxs out of the pipe anyway

Nope. One is located at the top of the dump and the second is located around 3/4 of the way down. Same as on the standard, minus the cat in between.

3MPS stock Dump pipe and secondary cat.




TurboXS dump pipe



TurboXS Cat pipe

[2XS]

You can also space the O2 sensor out and "trick" the sensor into thinking it is working fine.

[Ranton]

Hmmm

ok so only just realised that the Turbo XS pipe and the Cobb Racing Pipe do basically what I'm thinking and retain the Second Catalytic Converter..

is the Corksport Technically better as they claim due to the pipe work being port matched?

or is the bellmouth style pipes better?

---------- Post added at 08:25 AM ---------- Previous post was at 08:21 AM ----------


Cobb (similar to CP-e)


vs corksport?



hrmm

[2000MNLESS]

The Cobb system replaces both dump pipe and secondary cat pipe. CP-E does the same I am pretty sure.

Both TXS and CP are a two piece unit.

Not sure on the difference between teh ported mouth and bell mouth.

Personally I'd get the cobb system if I had my time again. But bear in mind, I don't think they sell a catback system anymore.

[Ranton]

Personally I'd get the cobb system if I had my time again. But bear in mind, I don't think they sell a catback system anymore.

Why would you opt Cobb

what did you chose?

[2000MNLESS]

Why would you opt Cobb

what did you chose?

Had TurboXS, had some fitment issues when I was just running it as a catback. So there was a bit of back and forth in motion. Once the full system was fitted, was fine.

Their system is/was loud. At the time they didn't have silencers avail for the system. Ended up having the 2nd resonator cut out and replaced with a highflow muffler. ... Sounded tough as nuts though

Personal pref for Cobb I suppose, just like their products and are priced fairly well.

Had their intake on my car and loved it.

[Ranton]

yeah well im looking at retaing the standard exhaust system.. i dont see any need to expand past the exisiting 2.5 inch system... i will never run big tubros or stupid hp so yeah.. if it was going to be 400hp plus id be all over a 3" setup.

however if i can just get away with dumping that first cat then yay!

[Doug_MPS6]

Not sure of your objectives here. The first cat and its sensor is the critical one for engine management. The second sensor basically just tells the ECU that the emissions going out the back are legal.

But the first cat is not the real restriction - the ghastly right angle design (see 1st photo above in 200MNLESS post) and multiple cranked bends of the entire arrangement, (including the second cat) out of the turbo is the biggest obstacle to clean gas elimination.

It's been designed by computer to fill a tiny space, with little regard to clean flow and getting your hand in there to service anything without dropping the motor on its mounts or even taking it out altogether.

Best thing you can do is put in a nice clean 3" dump pipe. It opens up the space in there, works well with the stock exhaust and sounds nice too, not noisy at all but purposeful, and much better in its overall effect than,say, a stock DP and a modded cat back exhaust.

If you are going to get your hands in there to mess with the cats, you're halfway dismantled anyway, so you might as well go the whole hog. You only want to mess with those heat shields once! It's cheap horsepower too!

[2XS]

I run a split dump pipe for power purposes.

The split design reduces turbulence between the wastegate and the back of the turbo (like an external wastegate setup) This was proven while I worked for CES, hence the reason they only fabricate split DPs.

The first O2 reads before the first cat anyway. As long as the 2nd O2 is after any cat, you won't run into problems.

The first cat being so close is a restriction.

The Corksport will get my vote. It could do with a better flow design where the wastegate pipe re-joins the DP and just before. I'll post a picture later

[Ranton]

i agree with 2xs on this in terms of the 1st cat being the major restriction.. logically it seems to me the gassses dont even have the opportunity to accelerate they basically are trying to move with the anchor holding them back..

i feel 3.0 is unnecessary the turbos in these are freaking midget..
i had a 2.5 inch downpipe on a K03 turbo once it was way to big the turbo over spooled to crap but had no lag.. the k04 isnt all that muich bigger... i just dont feel 3.0 is 100 justified.. bigger isnt always better... its generally different...

something that applies to everything... "For every action there is a reaction"

[kagerou]

personally, i dont see any difference between either of the manufacturers for downpipes, anything would be better than factory
if you're not aiming for big power, then just go with whatever is cheapest, and will fit with the factory cat back, otherwise, get a CES system for the split wastegate

not sure if the corksport will work with the factory catback, so contact mpsgarage

if you can be bothered doing it yourself, then its worthwhile punching out the first cat, if you cant justify the cost of a downpipe since they are over $1000 delivered

if you get that emissions error, then do the resistor trick, space out the rear o2 sensor, or just ignore it, unless you can be bothered relocating the rear o2 sensor, but that means you may have to extend the wires for the rear o2 sensor since they dont have much more slack in them

i dont know how the engine would go with a 2.5" downpipe, but a 3" really improved the mid range when coupled with the factory cat back from my experience

i actually prefer that setup over the current 3" cat back i have now, which is more focused towards higher rpms, but then i like the sound of the current system, and there actually is a point to revving out to 5000rpm now

if you want a factory down pipe to experiment with then i have one available as well

[lazydog]

The TurboXS doesn't have a cat in the downpipe btw the o2 sensors from what i can see. Looks like a similar bell mouth to the CPE/COBB DP. The Corksport is the only Downpipe that has a divorced downpipe which is meant to be better for spooling up( ie comes on a little lower than a straight bell mouth design). What's better? that's up for discussion.

Having said that, I had to get a custom cat made up to make my exhaust straight through system cause the stock cat isn't good enough.

The CPE and Cobb ones are the only downpipes that bolt directly up to the standard cat back exhaust AND contain a proper High Flow Cat in it. If i had my time again, I would be going for a CPE Downpipe...