After reading the tread by Fasteddy1, where he did this to an M240i, I decided to give it a try. Thanks Fasteddy1 for the inspiration. (Check out this link -
http://www.2addicts.com/forums/showthread.php?t=1357273) My objective here is more of a conceptual how-to, with pictures of some major steps along the way. One of Fasteddy1's comments was not to attempt this if you don't have extensive auto body experience, which is probably good advice. Personally, I've prepped and painted a number of cars over the years, molded on fiberglass fender flares, and fabricated a custom chin spoiler and rear spoiler out of sheet metal, but all for myself, not professionally. However, I'll say that a lot of the skills, tools, and techniques I used on this project are the same I've used as a homeowner installing tile, cabinets, paneling, repairing sheetrock, etc. Bottom line, it's more common sense and basic manual skills, and not rocket science.
Parts list and approximate prices, most all bought off of this forum, Ebay, and Amazon: M2 Exhaust - $350; M2 rear diffuser - $100; non M Perf. F22 rear diffuser - $100; 3M 04240 adhesive - $45; 3M 05887 filler - $45; 3M 08571 "caulk gun" for the adhesive and filler cartridges - $55; 3M 05907 adhesion promoter - $35; SEM flexible primer spray, 1 can - $15; SEM flexible bumper paint, 2 spray cans - $35; SEM Bumper Bite flexible glazing putty - $25; Misc. supplies - Denatured Alcohol, sandpaper, masking tape, disposable gloves, etc., $35; Total - $835. On top of that I bought a replacement muffler heat shield in case I want to go back to stock - $50; a spare Exhaust clamp just in case - $35; and Active Autowerke's brushed stainless exhaust tips, because I didn't like the look of the chrome ones - $260. Extras - $345.
Was it worth it, hard to say. My wife and I both like the way it sounds, a bit deeper, more aggressive sounding, but at idle it actually seems quieter. At low speeds, light throttle pressure, (25 MPH limit in our neighborhood), it seems like the engine revs up quicker, and shifts sooner, maybe due to less backpressure? From a looks standpoint, as the last pictures show, the exhaust tips seem too low, and angle down a bit. Not sure if it's individual differences between cars, mufflers, or a difference in the bends and angles between the M2 and M235i exhaust center section, which I did not use. I'll cut the inlet on the muffler, angle it up, and weld it back to fix both those issues. The tips also stick out further than stock, but that's because the non M Perf. rear diffuser is "flat", and doesn't have a kick out of about an inch like the M Perf. one does. I've got a fix in mind for that too. Either trim back the tailpipes and tips some, or, do another version with the M Perf. rear diffuser and an M2 diffuser.
Other looks issues? The "body work" is not perfect. I'm not a professional, I did it in my garage, painted it outside with spray cans, and probably rushed a step or two here and there. There are a few pinholes in the final coat of putty, and a few small "globs" of paint where the spray cans "spit" rather than sprayed. However, it's all down low, you can't see any of it when you're standing up, and certainly not when the car is moving.
Sorry, but no sound clips. I tried, but for some reason my phone would record video, but not sound. I wonder if the initial start up and "bark" of the exhaust overloaded the mic and shut it off? I had it pretty close to the car, and right at exhaust level. It recorded fine when I tested by just talking. I know there are videos and recording of the M2 exhaust on an M235i and 240i out there already.
So here goes the "conceptual" step by step instructions. Obviously a lot of details and "how to" were left out. Overall, I probably spent 25-30 hours on the project over the course of 2 weeks. There was a lot of down time waiting for glues, putty, and paint to dry between coats, set up and clean up time, running out for supplies, etc.
Picture 1 shows the initial cut out on the F22 diffuser, from just outside each of the single exhaust outlets, and just above them. A lot of eyeballing and marking up with a Sharpie before making the first cut. I used an oscillating saw and Dremel tool with a cut off wheel to do cut both the diffusers. Pic. 2 and 3 shows where I cut the small center section off of the M2 diffuser to get it to fit tighter to the F22 diffuser. After the initial cuts, it took a few more trial and error cuts to get them to fit better. Pics. 4 and 5 show a trial fit of the two diffusers just sitting on the floor, from the front and back. Pics. 6 and 7 show how the exhaust heat shield was cut to fit around the tailpipes of the M2 muffler, and a piece of aluminum angle I added to attach the M2 diffuser portion to. Used a jig saw and tin snips to cut the heat shield. Pic 8 is a trial fit on the car, before gluing the two diffusers together with the 3M 04240 adhesive. I tacked it in a number of places first, let it cure, then went back a second time to glue in the entire seam. After doing the front, I took it off the car and did the full seam on the back side as well. In all I probably removed and put back on the original diffuser, and my "new" one a dozen times to make sure it fit and looked the way I wanted. It's actually very easy to do, and I didn't even break one tab on either diffuser. Pics 9, 10, 11 show the diffuser after being filled, puttied, molded, sanded, primed, and painted. I used a 1/4 sheet oscillating sander to do all the rough sanding and molding in, then a hand sanding block and sandpaper wrapped around a piece of 1" PVC pipe for the final contouring. Started with 80 grit and went to 100, 220, 320, and 400 before it was all over. Pics 12 and 13 show it on the car, and you can see there is too much exhaust tip showing, and they are angled down slightly. But, that's all fixable.
If anyone wants more info or details, PM me, I'm also willing to talk and discuss if you'd like. And, if anyone has a F22 / M235i M Performance rear diffuser they are willing to let go of for a reasonable price, PM me, Already have another M2 diffuser to mold onto it.