Removing cats
 

I saw there were a few thread on this topic already but there was no real concensus on which or both to remove.

I am defiently getting rid of the stock resonator.

I also want to ditch the cats and put angle block spacers or spark plug antifoulers before the secondary o2 sensors. I am fairly sure my cats are clogged as (60k on the car) as after a nice pull there is a smell coming from the exhaust.

Has anyone removed cats? Which ones?
Primaries?
Secondaries?
Both?

VRP replaced my resonator with an X pipe and put in straight pipes for the secondary cats (which have no sensors). Maybe Vadim will chime in on any plans to sell the setup.

I thought a nice smell on richness was a sign that the cats were working? I dunno about this stuff......

doesnt smell like richness. smell like rotten eggs - which is a sign of clogged cats.

thanks for the input jangy. so no check engine light with removing secondaries :)

Nope, no problem with that. Just cut them out. There is not a sensor anywhere near them.

No cats on my ride, just some small aftermarket resonators.

sounds good. thanks.

i will start with them and if that doesnt work i'll cut the primaries out as well and run an angle block before the o2 sensor and it should be fine. people used to do it on the mkv GTIs and those things threw check engine lights with 100 and 200 cell cats.......and the angle blocks went CEL free with test pipes

e55? get check engine light?

How much did that cost ya if you don't mind, also any CELs?

And more importantly, did you notice any gains?

quick pic of what i want to do for the 2nd O2 sensors to avoid the CEL
https://i15.photobucket.com/albums/a...wayne92slc.jpg

Haha!! Actually, not sure yet. It had leaks and stuff when i saw it. It should be clean and ready to dyno today. I am hoping for any top end gains. My dig is huge, so I really want a way to get to 150 pulling strong.

Also, I think my VRP/Powerchip tune has the O2 sensors turned off, so I get no CELs from that anyways. That is just what I think my datalogger was telling me. I dunno. Either way, no cels at all and you would not. There are no sensors near any of the work I've had. I left the primary cat and o2 sensors alone. All else is changed, except the mufflers.

i too have 2nd cat removed...
no CEL no issues... :y

Just 2nd cat removed? Did they just prefab something to fit in it? Also did you notice any gains?

yes. u won't pass smog if u remove both cats...
removing 2nd cat allows to exhale better than b4... :y

got the resonator and the secondary cats removed over the weekend. cost me 180$ for parts and labor. car sounds sweet,just a bit louder when cruising but when going wide open throttle it rumbles :)

definetly happy with the outcome and the cost, highly recommend this.
as far as power goes, its hard to tell small gains on a car thats almost 500hp. hehe. plus my stock heat exchanger pump is on its way out. johnson cm30 should be here today or tommorrow so i will go to englishtown to see how much better i can do than 12.7@109.

Who did the job for you? I am interested in removing my primaries....

does ur car only have one set of cats?
i heard the sl 65 only has one were as the sl55 has 2 is htis true?

my buddy owns a Meineke few minutes away from my house (i'm about an hour away from ETOWN), they do good work.

Yeah only one set of cats....I figured they would free up some ponnies, but of course will throw a cell light. Wonder if I could trick it with some simulators...Hmmm.

Ok, got you.

yeah you should be able to trick your sensors with the angle block things i posted pictures of or maybe the old spark plug anti fouler trick. they run about 70 a pair shipped for the angle blocks. guy has them machined for this purpose and i haven't heard of them not working. i believe my emission is due in February so after i pass, i will take my primaries out (just in case the angle block doesnt work i'll have a year to figure out what to do)

Could always get a tune and a pulley, they could program out the CEL code of the primary cats out.

Okay, you guys are definitely speaking a foreign language to me so I apologize. But, this forum is for asking questions, right? I've been reading most threads for a couple months now to learn as much as I can. Anyway, the one post I came across on this thread reference the smell of rotten eggs. After running hard and parking in my garage, I've noticed this smell. Does this indicate any problems I should be aware of?

Thanks.

:confused:

that simply means your cat(s) are clogged and probably robbing power. maybe its time to get rid of them or replace them with higher flowing ones if you dont want to increase the sound at all. hope this helps!

i had a similar smell and it got better after i removed the secondaries, it has only been a few days but i haven't noticed it be as bad as wehn i first got the car.

replacing cats with OEM units is outrageously expensive, so aftermarket or catless is theway to go:y

More ignorance here... is that a warranty issue? Are there CA emmissions considerations? If no to both, any suggestions?

you asked what it means you have the rotten egg smell? that is a tell tale sign you have an issue with a clogged cat. if your car is under warranty then why not just take it in to the dealer? :nix:

anytime you remove cats you run the risk of not passing smog. thats why i mentioned replacing with after market high flow cats if warranty has expired.

The rotten egg smell is a sign that the cats are working overtime. This is most likely due to misfires. I suggest changing the plugs, air filter etc. I bet the smell will disapear.

Now if high performance is your ajenda then consider removing the precats and replacing the main cats with high flow units. This will give you 99.9% of the performance of a catless system and still be green friendly. You will be able to pass emissions out the tail pipe. The lack of pre cats only affect cold start emissions which nobody test for.

Good feedback C32. So, what kind of power gains can be expected from that type of set up? Also, does it void warranty? My second issue is I just bought this thing CPO so you would think it was have just had a tune up... I think I need to get a repair history from the dealer.

Working overtime, exactly.. when a cat gets too hot it restricts exhaust gas flow. pretty self explanatory after that.

The dealer will only perform service based on MB dictated life cycles. I have seen spark plugs fall well short of what they expect them to. Simple minor tune up will yield real gains.

I had my secondary cats removed on my C55 and picked up 13whp and 19wtq Then a week later i went true dual exhaust with custom xpipe 2.5 inch dual pipe all they way back mated to the stock mufflers and picked up an other 6whp and 6wtq on top of what i already gained.

here is a sound video of my C55 with no secondary cats no resonator and true dual exhaust. I got dyno sheets in the C55 section if you want to see them.
http://www.youtube.com/watch?v=1da_AKDISho

This forum is really helpful. I just got off the phone with the "service tech" at the dealer and he mentioned that plugs, etc. aren't due until 100k. He also was totally unfamiliar with what I was talking about including the rotten egg smell. I think the program here will be to get a "minor" tune up done (whatever that entails) and see if the problem persists. As far as modding the exhaust goes, I really want to do that... but, not yet. I want to drive this thing for a bit and then decide on my game plan. Plus, I need to save a few $$$ first.

I hope nobody ran leaded fuel in the car?

yea, you can kiss those o2 sensors goodbye.

Besides plugs and filters what should I do to improve cooling/flow as part of the next service?

Has anyone tricked the primary 02 sensors with the simulators, I am really considering those....

Yes the sensor blocks look interesting. Can someone post or pm me in the proper direction.

secondary cats
 

I took my secondary cats and the resonator out it is now 3" piping all the way back, it sounds good. There are no sensors before the secondary cats. It also improved throttle response a bit.

the angle blocks are machined by a member over on the VW forums. they are very popular and work really well on late model VW/Audi cars. the space out the sensor as well as add a 90 degree turn in front of it decrease the inside diameter (similarly to oldschool spark plug anti fouler method).i am fairly certain tehy will work on mercedes as well, i am waiting on him to get me a set (about a 3 week wait right now) and i will get rid of the primaries.

after i try them and if they work we can ask him to do a group buy for everyone else who wants them.

do you feel that you lost any tq? this mod seems so obvious to gain power but, i hear conflicting stories about this.

i did not feel any loss of torque with this mod in my car

let us know how you do at the track after your new mod.

A friend of mine had the rotten egg smell after time when he drove to and from work over a steep hill about 3 miles long. The Service Tech told him to try different gas brands and come back if the smell goes doesn't go away. So far, the smell is gone. Go figure.

You put in 3" pipes? The OEM pipes aren't 3" is why I ask.



Here is the conflict. If you remove the exhaust, then you have no back pressure and therefore a loss in power from the SC. VERY similar to raising in Altitude. As you mod the car, it will be able to push more air and then some drop is efficient.

backpressure is the by product of exhaust velocity and scavenging, it in itself isn't beneficial in any way. lysholm supercharger(used in the 55k) is similar to eaton/roots supercharger. roots blower was a way to get rid backpressure and still have scavenging and velocity which would be ideal. of course, every car on the road isn't going to be running a roots blower...


Earlier cars (and motorcycles) with carburation often could not adjust because of the way that backpressure caused air to flow backwards through the carburetor after the air already got loaded down with fuel, and caused the air to receive a second load of fuel. While a bad design, it was nonetheless used in a lot of vehicles. Once these vehicles received performance mods that reduced backpressure, they no longer had that double-loading effect, and then tended to burn valves because of the resulting over-lean condition. This, incidentally, also provides a basis for the "torque increase" seen if backpressure is maintained. As the fuel/air mixture becomes leaner, the resultant combustion will produce progressively less and less of the force needed to produce torque.

another words i do not see how the backpressure issue can be an issue as in a case of our 5.5 with lysholm blower more air can be pushed in than can come out (even in stock form) therefore gains can be had from removing restrictions in exhaust. i would not run a bigger diameter exhaust though because the stock one is big enough

Can you explain that? I've always seen the intake side as more restrictive than the back side so i am a little confused on what you are saying. I know for a fact that even cutting resonators on an OEM car will drop some TQ.

i am not saying intake is less restrictive there are gains to be had there i.e larger throttle body but unlike a naturally aspirated engine the lysholm supercharged engine has a build up of air pressure ready to be fed in and it's waiting to be forced into the combustion chamber.

example a garden hose ...
Sure you get more velocity out of it with your thumb over the hose, and the water pressure is higher in the hose, but the pump at the other end has to work harder to push it! In an engine, the "pump" is the piston... you don't want to make your pistons work harder, do you? The only reason you make more power with smaller pipes converging into a collector is because the collector provides scavenging, and exhaust velocity contributes to this effect. There is a fine balance between exhaust tubing size and backpressure, too small is too much of a restriction and negates the scavenging gains, too big kills velocity and therefore scavenging. In a perfect world, the piston would push all the exhaust out of the chamber on its own.


i would want to see a dyno of a 55k loosing torque to really believe it. even then dyno of the same car can vary so much even if it is done the same day on the same dynometer......in the end even a dyno would not show much so it will remain a matter of preferance and what people choose to believe.

well spoken prodigymb. i do agree with picking up power with less restriction. especially on a f/i vehicle, (actually common knowledge) but a lot of urban myth has risen about this topic and some do believe the ecu have a negative effect on power output. (or something like that) after being a long time advocate even i am doubting touching my cats untill i get a tune. :scared::shakehead :wall:

Another thing to keep in mind is EGTs. I am not sure if the O2 sensors in MBs read the precat exhaust gas temperatures, I would assume they do. The more restrictions you have the higher your EGTs will be, high EGTs will make ECU pull timing. (should not be an issua at stock boost, but with higher boost levels it may)

Max.H you are definetly right on being able to capitalize on the power gains from less restircitve exhaust through tuning.

where is the shop located...i am interested in doing the same to my e55...

are the secondary cats the ones closer to the rear of the car?
so basically if i remove the secondary cats and the resonator i can still pass air care (emissions) tests and i wont get a cel?

yes.
yes.

google meineke in 19115. tell them mark with black e55 sent ya :y

when changing the piping did they use stainless steel pipes or just regular metal?

for me, only the x-pipe was stainless steel...

mine were done with mild steel not stainless. most meinekes dont weld stainless as it is harder and more time consuming. in my GTI i had a stainless system built at a fabrication shop but that runs more money nad i didn't feel like spending it considering mild steel will outlast my ownership of this vehicle.

same peple built a turbo back exhasut for my very first car 5 years ago and that exhaust still looks great.