Just got my car straight piped. I am really enjoying the sound that it is putting out. I'm coming here to ask you guys a couple questions about it. A little bit of backstory first. I simply went to a small town muffler shop and had them straight pipe the resonator and both mufflers. 100 bucks easy. Haven't tuned or done anything else to the car. Some people claim that you must tune certain parts of the car to accommodate for the straight pipe or else it will "damage" the engine or lose performance, which leads me into my questions:

1. Do you guys think that this has had any performance effects on the car, good or bad?

2. Do I need to do anything else to the car to accommodate for the straight pipe?

3. What do you guys think of the sound? (The exhaust is actually really loud, my phone doesn't really pick it up that good though.)

 

Update: So I now have a check engine light on. Air intake system leak. Code P2279. Is this from the straight pipe? I don’t see how I could be getting a code from the resonator and muffler being straight piped.

 

1. Not until you get an ECU tune. The car is already programmed to be putting out so much exhaust. You would need to tune the computer to take advantage of the extra flow.

2. A catalytic converter.

3. Meh, a true aftermarket exhaust wouldn't sound as loud and wouldn't get you breaking many sound laws (these exist depending where you live or travel through)

Your check engine light is likely caused by the car not recognizing the pressure or gunk in the output that is coming out of the exhaust. Your O2 sensors are likely causing that code (if they are still there). If they arent, you would see that code also.

Straight-piping is not the most responsible or safest way to get a better sounding exhaust. In my opinion, you would have been better off spending $400 for an exhaust that wont throw a code, still increase performance, and not make your car sound like a Honda.

These are very nice cars and I guarantee more care went into engineering the E-class than every other car in the midsize sedan market segment. Don't mess with these cars like that, they don't like it.

 

The code is the cooling air that was feeding the muffler bearings. Said air is now free flowing and it sees it as a leak.

 

Sorry, I couldn't resist... I don't see how the code is related, but who knows.
I would put some free flowing mufflers on it to tame that annoying sound. The only mufflers I've had that were actually full and free low were DynoMax Race Flo. They work and sound awesome. I use them on my Chevota and any other muffler I tried would will kill performance. The drawback is they're packed with fiberglass, which is awesome but it breaks down over time. You may not have an issue but I did so I had to repack them after a couple years or so. I had the ovalish shaped ones so I simply cut a 2" hole on the aft end on either side of the exit pipe, then I pack it tight with regular house insulation fiberglass using a stick and a mallet and she's good to go. I made 2.5" covers for the holes made of .062" steel with four holes for screws. The machine screws thread into the muffler body. So super easy to repack any time I hear it getting louder.
Ironic story: Dynomax guarantees the fiberglass to stay put for life, but in order to prove it's not there anymore you have to cut it open, which voids the warranty. I was pissed and argued with them over the phone, but basically they want to make the claim to boost sales, but they don't actually want to honor it. Again I don't think you'll have issues but I don't know for sure, all I know is my motor was extremely hard on them, far more than a 3.5 V6.
Just an fyi that they flow as well as a straight pipe but greatly reduce sound and what comes through is a super sweet tone. They do not sound like a flowmaster at all, which I call a flowclogger, and they sound like an open pipe exiting into a 55gal steel oil drum. I hate those things but their advertising campaign was good and brainwashy so people buy them. The Race Flo filters out all those high pitched noises leaving a nice deep bass tone. I had one old retired racer neighbor tell me he gets a hard on every time I hears me. I gotta admit, it's the best exhaust note I've ever heard and I think it would be perfect for you. I actually think maybe just one 2.5" muff where the resonator was would work great. Have the two pipes Y into it and Y out. They make 3" too, if you think you need it.