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.