dohcfiend

I took a brief look underneath the car and to my surprise didn't notice any sensors monitoring any of the converters. I have never heard anyone talk about deleting all 4 so there must be another reason you guys leave the top 2 alone. Will deleting all 4 cause the engine to run incorrectly?

MarcusF

If it is a U.S. spec car, before and after the forward most converters are O2 sensors – a total of four. Looking at each exhaust bank, the first O2 sensor (closest to the engine) is used to control air fuel ratios when the engine is in closed loop mode (idle and cruise). The second O2 sensor (after the first cat) is used by the ECU to determine catalyst deterioration. IE, whether the primary cat is still working. It does this by observing the variations in oxygen content of the converter processed gases. That's why people leave the first cats in place - without it they'd get a CE light.

dohcfiend

To summarize then its not a matter of functional issue like burning valves but simply an ecu issue.
I see, I guess I just didn't see the o2 sensors behind the first bank. Do any1 offer o2 simulators for this application? Hmm I wonder if an o2 simulator could be spliced into a mb pigtail? Just thinking out loud but I would imagine an obdii o2 sensor would function the same for a german car as an American car hence an o2 simulator would function the same. I may need to dig into this a little.

dohcfiend

Any1 care to donate for research? I have a spare sim laying around; all I need is a wire pigtail from an o2 sensor. Don't care about the sensor itself whether it works or not. I'm also going to ask the dealer to see if they have any busted o2 sensors I can have. Other than that some wiring data would be nice. I imagine it's a 4-wire o2 sensor. 2 for sig and 2 for heater. Need color code or preferably a pinout for that sensor. Also info about the operating range of the sensor signal for the Benz. As I understand it obdii is a standard and as such the equipment should be similiar if not the same in operation.

bcarpman

I'm new here, but NOT new to custom vehicles. Been doing this for a LONG time. Many of us may not remember how bad vehicles stunk back before CATs but they did. Sitting at a traffic light was often an eye watering experience. Personally, I can't imagine wanting to own a vehicle without them, unless it's an original '67 vette. Get rid of all four converters, and you'll be giving up a major peice of refinment and I'd have to wonder why start with a MB in the first place.

Not trying to lecture. Everyone has their own standards. Just hate to see someone go to a lot of trouble to remove the front converters and reprogam the ECU, just to find out you no longer like driving it.

MarcusF

I've posted before, but here's something to think about: The 55 has a 331.9 cubic inch engine. Using 100% volumetric efficiency, at 6000 RPM, a 331.9 cubic inch engine could theoretically flow 576 CFM. However, that's not going to happen. In practice, unboosted engines can't achieve 100% VE at 6K RPM, but we'll use that number. The 55 exhaust path causes the cats to only see half of the exhaust flow, so the cat has to be able to flow 288 CFM. Magnaflow 2.5" inlet ceramic cats have been flow tested at 372+ CFM each. That's about 130% of what's needed using inflated engine flow numbers. Metal cats can flow 200% of what a 55 can flow.

The O2 sensor color codes are here.

dohcfiend

Everyone is entitled to their opinion and i respect that. There is no ecu reprogramming involved with installing an o2 simulator. If it
works, it's a fast and simple procedure. As
far as the eye watering stuff, well the exhaust comes out the back so that's the other guys problem. But to counter the mb in it's purest form; the German spec doesn't have cats as I understand so coming closer to that would make it more of a thoroughbred not less.

betrezra

Bcarp - alot of the bad smells from cars in the 70's / 80's was due to no cats AND poor running (Ill tuned carb'ed motors). Ever been behind a poorly tuned all orig 66 mustang? We have one, and I have to keep up with the points/carb settings to keep it running right. When out of tune it puts off the horrible smells you talk of.

The modern fuel injection will not be as bad..... you can remove cats from a modern fuel injection engine (assuming stock cam), and not get this situation.

All bets are off with offroad exhaust (no cats) + modern fuel injection AND aftermarket cam(s)....... then you're back into the smelly exhaust in some cases.

My 1cents worth

bcarpman

This is not for the Dohcfiend as I realize that pulling all four CAT's will work just fine for him and no offense was intended, but just to clear up some misconceptions for anyone browsing this thread in the future, I thought I'd add this.

- All german vehicles have had CAT's for at least 20 years that I know of. My work in emissions compliance for EU was limited, and the standards for deisel are less strict, but unless I'm missing something, all MB's have had CAT's for quite some time, as EU emissions standards for gasoline engines have basically piggy backed US standards for quite some time

- betrezra is correct that tune will have a GREAT deal to do with it, but most will still notice the difference in their own cars, even if you don't care about everyone else. It just depends on how sensitive you are, but unless you have a wife/girlfriend that loves classic cars, SHE will notice. If it's a cabriolet, the difference will be even more pronouced.

- MarcusF is also correct: unless MB was getting cheap on the CAT's on an $80k vehicle, or unless you're shooting for 700hp, I'd be surprised if you gained anything but noise. I'm not sure how much clearance there is on the front cats but a good set of high flow cats would definately flow enough for this vehicle, and you'd still be able to sell the car in other states with emissions test.

- Yes, I'm sure you can get by with 02 simulators, but personally, I'd never pull the close-coupled CAT's off a vehicle without doing a retune. There's a lot of interdependance going on there. It's a system. But I'm weird that way. I recal after every mod. Probably the main reason I won't be moding my CLK much: no one seems to make aftermarket tuning software for it like they do for virtually every US vehicle.

dohcfiend

- I read somewhere that implied that the European versions were less restrictive so it was am assumption on my part.

-my g/f has her own car. The CLK 55 AMG doesn't strike me as a chic friendly car(there are many exceptions I'm sure) as denoted by the ride quality or lack there of.

- I like noise, iirc there have been dynoed gains of 19hp by removing the rear cats and the resonator with no tuning. I do however see a benefit to it but not on the exhaust. Other than o2 content the ecu doesn't care what you do to the exhaust. Fitment will not be a problem bc I will just be relieving the cats of their guts. As with most peeps that decide to modify their cars, I plan on keeping it.

- doing a recal with every mod would be ideal but there are situations where it isn't necessary. There are quite a few members on here with heavily modded CLKs that seem to be doing just fine. I personally don't plan on going that far but you never know. Also just bc a car is not what you are used doesn't mean it's off limits. That kind of close minded thinking is just a way to stiffle innovation and if everyone thought like that we'd still have horse drawn carrages.

- I'm not trying to change anyones mind but I do see the need to engage against sleights both blatant and veiled. All in all you do or not do to your car what makes you happy. The descision is up to the owner; if the owners descision causes concern with others by all means voice those concerns. But at the end of the day the descision still lies with the owner to either reap the consequences or the benefits of.

dohcfiend

After doing a little research I'm going to go a different route. They make a different style o2 sim that's a screw in bung with a mini-cat in it and you simply screw the o2 sensors into the bung. If it stops raining long enough I will put my car on ramps to take care of the rear 2 myself and check fitment of the bungs on the front 2 to determine whether I need a straight or angled bung. Naturally I'll buy and test them before servicing the upstream cats. Also I'll give a visual to determine whether or not I want to service the upstream cats or have my mechanic do it.

dohcfiend

I ordered the 2 sims I need and made a visual. It appears the rear cats are flanged on one end and welded on the other. I think I'll just wait to get the sims in, test em and have the mechanic pull the exhaust and take care of all 4 at once. If I have the spare cash and if the OBX headers work out for that other guy I may have them installed with the exhaust.

MarcusF

Are you buying adjustable simulators? Double adjustable (heater and O2 circuit)? You may want to save the plugs from the original O2 sensors. All four plugs are unique (idiot proof, they can't be plugged into the wrong socket). Don't forget the anti-seize for the pipe plugs. Post back the results. The more details the better - simulator manufacturer and model. Thanks

dohcfiend

No these are completely different and cheap, but the idea is so simple. They can be found at bigdaddiesgarage.com. There is no modification required. Basically you remove your o2 sensor and screw this little 4 inch umm Thingy about the size of a 5/8 spark plug socket. Inside it is the same material found inside a converter and it has a threaded 18mm end you screw your existing o2 sensor into and you are done. They have straight and angle ones for clearance. Why I never thought of this earlier.....D*MN IT!!!!!

MarcusF

In case you didn't know, there are O2 sensor simulators that completely replace the O2 sensor. Pipe plugs go in the O2 sensor exhaust bung, and the O2 sensor wires go to the simulator. The O2 sensor simulators I'm referring to mimic the signal the ECU is expecting from the O2 sensor. In case they're slightly off, they are double-adjustable. One adjustment is for the O2 signal, the other adjustment is for the heater element signal. All that's needed to adjust one is a flat head screwdriver. If you come across one that advertises it can increase power, ignore the marketing hype. O2 sensors are only used at idle and at cruise. Maps are used for all other conditions.

Please post back your results from the device you listed. It doesn't appear that any exhaust would flow "through it". "Up to it", yes, but not "through". If so, it'll be interesting to hear the results.

dohcfiend

Will do. I think if bad comes to worse I would have a little piece of metal welded on it to "catch" some gases if necessary. But I don't think it needs much to "sniff" tho.

Chappy

Dohcfiend...have you dynoed your 55? Will you be able to measure any possible gains from modification?

dohcfiend

I'd like to but money is a little tight ATM. Mainly due to maintenance issues. I do plan on dynoing it tho. I wish I could get a before and after shot. It's only a partial victory but if my legwork proves fruitful perhaps someone with more resources could take the final step with their 55 and install/measure it.

Chappy

The first 208/55s arrived here nearly ten years ago. If the mod hasn't been tried and documented, you just may be the Guinea Pig....please let us know your results.

dohcfiend

Whistle squeak whistle.

MarcusF

Here's a cheap way to find if your mods produce more power. Real cheap. Buy a G-Tech on ebay. The old ones are about $20. Do a quarter mile pass and write down the G-Tech MPH figure. The street doesn't matter, as long as you can do it again later on the exact same street. Make your changes, do another pass, and record that MPH. Higher MPH usually means more HP. If you're worried about weather conditions, go to weather dot com and record the humidity, temperature, and barometric pressure – then do your baseline. Ignore the elevation, that won’t change. Then every time you make another pass, get fresh info from weather dot com. Plenty of sites will do environment conversions for quarter mile passes. If you can't find one, post it here – some of us have them on our PCs and can post the results.

Chappy

Excellent suggestion Marcus

dohcfiend

Sorry about the delay. Been raining. I installed the sims and they appear to work. I let the car run for about 5 minutes without incident. Next step is to get it to the mechanic and let him work. Things are a little tight ATM so it may be a few days.

dohcfiend

Mechanic should be done in an hour. I'll have results then. Not really going fast at performance modding. Have maintenance and appearence things to do first. I have 4 possibilites for performance mods tho. Modify air box, headers, ported intake or ecu flash if I can get a good value. I do however plan on starting a custom dual exhaust project with a fabricator soon but it's kinda in the middle of looks and performance. Different wheels is the highest priority bc the amg wheels suk IMO.

dohcfiend

Operation was successful. 4 cats are gone and boy was it alot of material. The exhaust has a hollow sound which is ok but I plan on more exhaust work. But dyno says 17-19hp.lol. Why I didn't get to gauge the result but I did test the parts and they work.