[...snip...] And the fact is that you can free up lost horsepower....but for the cost/benefit you get with an exhaust ... [...snip...]
I think your overall advise is probably pretty spot on.
I did my exhaust as part of my
first phase of work. But I hated the exhaust on my Z4 and we happen to have a shop in the DC area,
Mandrel Bend Solutions, that has
German Transfluid Mandrel Bender which can do center line radius on most bends is 1.5 times the outside diameter of the tube. Their digital design work and mandrel bend exhausts is awesome. They also have equipment to take measurements on OEM bends and replicate. - I wanted to leverage their skills and product (as sometimes stuff disappears). Cost was under $2k for 2.5" dual behind the downpipes, with high-flow mid-pipe cats, and mufflers. The exhaust was a work of art. Car should be driven upside down. I've attached a photo below - wish I had one of the fit over the axles.
I'm also a bit weird, strategy-wise, as I chose to build up my car to support the power, not the other way around.
Traditionally BMWs don't leave much of any power on the table with the exhaust. This has been true for a long time. Same with intakes. Same with air filtration. Same with programming, once Bosch (at the time) figured out how to do it (turbo changes that, I'm talking NA Motronic 1.0 days V1,2 ...). It was not unusual to school people new to BMW that changing parts could actually make the car worse because BMW did a pretty good job - they leaned toward performance. On exhausts their stuff was just heavy, but that plays in to other priorities, since their MO has always been balanced performance (handling/power) with comfort.
When we talk exhaust, we're really talking post downpipes on the N54. Those seem to be worth doing sooner rather than later. I suppose I could have pushed for a bigger exhaust system, but I'm working toward a road-race style build with no more than 600whp.
Filippo
