So the weekend before last, Tom and I set up to install a free-flowing exhaust on the M Coupe. I was pretty picky with what I wanted from an exhaust, the stock BMW M units are pretty good, albeit very quiet and thus quite heavy. I didn’t want a boomy american (or ‘rice’) sound just to shed some weight and add a bit of top end power, so I ended up getting bespoke exhaust makers Hayward & Scott of Essex (UK) to build me one. After a month of pounding on metal in sheds, the men from Essex sent me a hand-made exhaust. We waited for good enough weather to perform the install and got to work…
The process is easy enough in theory. In fact our biggest worry, seized bolts/joints was a non issue. The real challenge was fitting hands/tools in places to remove joints. We put the car up on four jacks, as high as we pretty much could. One of our jacks was low on hydraulic fluid, and was located at the back on the driver side, so we shuffled it to the front passenger side where it would be less of a determent. After playing with the jacks for awhile we were ready to begin. We began by removing the BMW back boxes. Each one was held on to two brackets, rubber mounts. Getting them off of the brackets was much harder than just removing the brackets from the body, so thats what we ended up doing. Each muffler was connected to the mid-section with two bolts and a metal ring, easy enough to remove. Removing the BMW mufflers, you really got a feel for how heavy they were, in excess of 30 pounds a pop.
With those removed we could focus on removing the mid-section. The mid-section is guarded by several heat shields, which also keep it snug with the chassis. Removing those was trivial. The mid-section is attached to the rear cats (the car has four catalytic converters in the North American spec) with six bolts. Removing the top bolts proved to be exceedingly difficult but we managed to do so. At this point we felt pretty pleased with our efforts. We began to try and jiggle and slide the mid-section out from under the car to no avail. It was being blocked by two large pieces of the rear subframe that cross the back of the car and add to the overall rigidity. After hesitating and trying to partially undo and move them out of the way, we gave up and removed both cross bars. This made removing the mid-section a snap, and we put it on the lawn with all of our other parts.
The stock BMW M mid-section is an X-pipe and contain a mid resonator, and was also quite a heavy part. The Hayward & Scott mid pipes we were replacing them with were a straight stainless steel X-pipe. This change reduces back pressure, reduces overall weight (although not by more than 10 pounds) and produces an awesome crackley overrun noise on lift off and during engine braking… After a short break, we installed the mid pipe, having similar trouble getting those top bolts in. After putting those in, we reattached the cross bars, and then put the heat shields back up. From there we were able to begin installing the H&S back boxes. We rotated and snug them onto the mid pipes until they lined up with the brackets. This wasn’t particularly hard, though the mid-section was not perfectly symmetrical (an issue with any non robot made parts), and thusly made fitment on the drivers side a bit trickier than the other.
We finished up, put the drivers side wheel, and lowered the car. I then proceeded to fire her up. The sound of a cold start was pretty impressive, you could FEEL it. Pretty soon the car warmed up and it became silent as it hummed a long in neutral. I took her out for a quick spin. Low revs are a bit deeper than I had anticipated, but the scream at high revs is just spine-tingling. Better yet is the sound between gear shifts, as unspent fuel burns up on the pipes and crackles out the back. This becomes more pronounced as the pipes heat up, to the point where a throttle blip with a fully hot exhaust is just incredible. Highway cruising is completely silent thankfully, however any throttle under full transmission load is quite a bit louder than I had anticipated. Superficial (though important, since you have to live with it) criteria aside, performance is fantastic. Though its really hard to say as the car has always had a ton of power put down to the road, so detecting a predictably small peak power improvement is impossible, we’ll have to book some dyno time to really know for sure.
The weekend after we did a bit more fitment work on the drivers side, as the pipe still sits crooked, more so when the exhaust heats up and expands. We’ve not quite gotten it perfect. I’m also not 100% happy with the volume level, it’s a bit TOO loud for my taste, though it sounds fantastic and raw, not synthetic and big-tippy. Never the less it’s been a fun project, however it turns out! Thanks to Tom for his hours upon hours of work.
The following is a video I made with a cold exhaust, the overrun is not nearly as noticeable as hot pipes, sadly. I had made a better one earlier but had completely forgotten to TURN THE MICROPHONE ON (as was the fate of my ‘before’ video). I might make another one one day, but I generally don’t like sitting and revving the engine like a child in place, its rather anti-social :)