Towards the end of last year, I briefly flirted with the idea of upgrading from my 128i to a 135i, then an E92 M3, but after a few months of searching and thinking, I decided I was at home in my 128i and decided to dump some of that potential down payment into upgrades instead. I already had the BMW Performance Exhaust installed, and wanted to keep to OE upgrades, but the performance increase seemed to good to pass up, so I purchased it back in January to commit myself to a plan and get off the car shopping kick. Had some questions before ordering which were promptly answered by Rob @ AA (more on this later) and was given a great deal on the parts & tune.
Before starting the install, I made sure to order an extra set of studs for the mounting of the headers to the cylinder heads (part #11127593376, qty: 16).
Ordering these extra is STRONGLY RECOMMENDED. My car has been in the northeast its whole life, and many of the stud nuts holding the OE manifold in had corroded and fused themselves with the original studs, so most of them came out together. AA provides 16 new nuts and 4 bolts/nuts for the exhaust flanges.
Did the install in a helpful friend's garage on jackstands. SEVERELY underestimated the time it would require to do this job. Took us around 10hr to complete the job due to some complications, pitfalls and needing some better tools.
For starters, the workspace is very cramped. I made another thread asking about how best to attack the stud nuts for the manifold - I would highly recommend a
flexible-head ratchet and a
flexible box wrench. I'm pretty certain there's no way we could have completed the job without that flexible box wrench, though maybe one with an offset would suffice. As I mentioned, the car has been in the NE, and seen plenty of salt/snow, so the exhaust manifold-to-straightpipe flanges were also fused together, along with the bolts. Due to the cramped space, getting these apart was no simple matter either.
First thing to disconnect were the O2 sensors. I taped off both sides of each connection to make sure I didn't screw up which sensor went where when we re-installed. I put one piece of masking tape on both sides of the connection for one bank, and two pieces of tape for the other. Left the sensors plugged into the original manifolds and pulled the cables when taking the manifolds out to make removing the sensors from their sockets a little easier.
We double-teamed the stud nuts, one person underneath, one person with an arm down the engine bay from above. We generally needed one person to guide the socket/wrench onto the nut, and the other person to wrench on it, so highly recommend having two people for the job as well.
Once all the nuts were off, getting the old parts out, and the new parts installed was just a matter of will and figuring out how to contort our hands to get access.
After everything was put together, buttoned the car up and started her.
HOLY CRAP it was loud. I mentioned the questions I asked AA before ordering - one of the questions I had asked was what the NVH impact was going to be like given that I had the PE, I was concerned about it being loud, and they had said that it would be "minimal", but this was far from minimal. Sounded pretty badass, but had an incredible resonance from ~2000-2400 rpm that rattled my windows and floorboards. While the performance increase was awesome, the volume increase made me quite self-conscious driving home, wasn't exactly what I was hoping for after hearing such good things about these headers. The car also picked up a nasty idle surge that was causing the car to jump from ~600-800rpm and shudder pretty badly. The next day, after driving to work and sitting in the parking lot, car threw codes: 29D1, 29D2, 29D0, 29CC, 29CD - Misfires cyl. 5, 6, 4, Multi, 1. Cleared the errors with AA's Simon3 tool and they did not come back, but I was hesitant to drive the car a whole lot at this point.
I went through about a week of back-and-forth with Nic @ AA (very responsive and helpful) trying to troubleshoot the idle surge and potentially get at the root of the volume/resonance as well. I tried resetting the throttle adaptations using the instructions on AA's website, and the instructions on these boards (which vary slightly in how the throttle comes into play during the process). Retorqued the exhaust bolts, verified my O2 sensor connections several times over, took apart the EVAP system in case we had bumped a hose or something - no dice. Finally, today I think I made some progress:
Last night, I had installed a new M-sport steering wheel (courtesy of
idk alex great seller!) and had the battery disconnected while doing so. This morning when I started the car,
the idle-surge was gone. Car was still loud as hell, but the rough idling was gone, so that was a relief. Not sure why this is, but my guess is that maybe that *actually* reset the throttle adaptions?
I also removed the BMW PE and reinstalled the OE exhaust. Huge difference! When AA said that the NVH impact would be minimal, this is what they must have meant - could barely tell the difference from stock. I'm a little sad to lose the PE (I really liked the tone and look of the pipes), but I'm very happy to get back the liveable volume and retain the performance bonus of the headers.
In summary: AA has been a good company to work with, both for the purchase and their support. Headers definitely give a performance boost (have not dyno'd but plenty of others have). If you have a BMW Performance Exhaust, be forewarned - this upgrade will make your car loud as shit.
Sorry for the long post, but I just wanted to capture my thoughts and problems in case someone else goes searching for the same thing and has problems.
Cheers!