I know this has been asked before but I keep seeing conflicting answers, some say backpressure after the turbo is bad and you will have more after gutting the cat, and some say that it’s good. I haven’t seen any of these threads recently so I’m curious if anyone has any dyno or otherwise evidence of performance and/or mileage gains after removing the cats.

I was not aware the ‘06 came with a DPF, is that seated before or after the cats?

Triumph 2300cc Rocket III in tuning


MV Agusta F4 CC getting fueling and insane spark mapping reflashed


Aprilia RSVRRR with SC Project “pipe” such as it may be.


Stupid I know....but $3k at 151k miles with current services...AWD, and easy increase in power plus surprisingly good on fuel
I have a bunch on of turbodiesels stuff including a couple Mercedes. My 06’ OM648 has been my mod monster. For me as I do dyno tuning daily on Motorcycles I have a somewhat unusual opion of dyno work. On my cars/trucks/toys I avoid it, kust use a $10 App usually which if you do two way runs, actually weigh car, actually input rest of required values....like Cd and Cda and gearing and tire data accurately...it’s within a perfect or 3 of local dyno shop. I just updated to the newest version of performance pro, the one I like best after many years away to play with my new/used Audi D3 and I guess I accidentally deleted my library of previous data because now I’m digging around for CdA on every car I play with, gear and final ratios and making regular trips to local recycling center to **** them off by just weighing car in drive through, thanking them and leaving. Sometimes I donate to beer fund because I do feel a little guilty, got a nail last time though in A8L tire so next trip, no beer money.

I use a Mustang dyno for work which I’ve owned like 15 years now. It is one trustworthy, reliable machine, and while it reads 15-20% lower than a DynoJet it matters not to me, like the App based stuff, I just want to see changes and deltas. Datalogging in cars which I did for about 5k miles before first reflash in Benz teaches you a lot about what the car is really and really not doing. Gotta give me a break I cannot find my 8 or so year old log files before/after each change but for me, on my carbwith a clean oxidation catalyzer located less than 100mm from exducer hot side exit, straight piping was absolutely the way to go. Suffice it to say other than a tiny noise increase (had stock mufflers at this time) time-to-boost and a small increase in outright boost pressure for a given amount of fuel injected or motor load were the results. In time I actually allowed less fueling than stock in some parts of lower rev range and did end up straight piping the car.

It only sees a true full power “cleanout” type pull a couple times a year. If it has been a full 20k miles between hard runs a tiny bit of carbon does come out the exhaust in the first gear or two. I see the same thing on the dyno with higher mileage street bikes with stock and aftermarket pipes...the old Italian tune- up, sometimes it takes a while to burn chambers, ports and valves free of carbon as well as exhaust headers, manifold and cats if present.

I take a TON of pictures during the process, it’s visually spectacular lol. In the last couple years I have added option of water or water/methanol, isopropanol etc injection for a proper steam cleaning. Borescope pics before and after of engines on disassembly really look nice inside, it’s way easy to spot dead flow area of ports and dead zones in combustion chambers too.

Back to Benz related stuff. I did EGR in mapping and catless downpipe at the same time, then proceededed to drive to Reno Nevada for Air races and back to Central Texas datalogging the whole way. I always do a mathematical calculation of my fuel economy. On same sort of trip I was getting a true 27-29mpg STOCK, now making more power and running better I had a best tank of 43.7mpg and averaged 38.5mpg for the 4K mile round trip. My mixed driving commuting average for the last year is about 34mpg on that car. Not BS numbers from Benz dash lol. Way more accurate and less optimistic than my Ford truck 7.3 turbo Diesel with same basic mods but still the dash suggests higher mpg than reality.

I sort of figured with the Audi I can play with up to $2500 worth of work and mods before I even get too close to loosing money on a quick sale. 4.2 TDI Motor and trans isn’t that much money if motor popped anyway...that could be way fun.

The benz is a a total loss financial situation at this current mileage so it is my real toy car I guess. Throwing stuff at it over winter, maybe results will be better than expected but in the end I’m just shooting for 320 bhp or so and great economy. It’s my daily driver until some moron smashes it to bits in Austin traffic, then I’ll either get another and transfer parts or part out after getting insurance money and buying back? Worst case scenario lol, car is unkillable and I drive it till something truly expensive breaks? It’s a fun car, wish it were a manual shift but, it does great at almost everything I ask of it.