I am able to get a 2.5" custom made stainless steel exhaust with a turbo muffler fitted to my 87' 735i. What effects will this give?? good or bad all suggestion will be appriciated. I can get a custom made sytem made up any size and specification so any suggestion will help.

I live in Australia so i dont wanna import but have a friend that can make a custom made one!!

Thanxs

I've been looking into an exhaust change for a while. Increasing the pipe diameter can actually reduce low-end power. You need a specific amount of backpressure for the low end, and the diameter of the header and distance to the muffler is calculated by the diameter & length of the intake runners, cam lift & dwell, the desired RPM you want the power to come at as well as numerous other factors. A free-flow design could be detrimental, and only give an "aparent increase" in power due to the increased noise. At best you'll gain some at the top end, but you'd be better off with low end torque in my opinion. The OEM muffler is most likely the one for which the most comprehensive developement was invested & likely your best choice.

There are many brands out there, enough to get well confused. Supersprint is one of the more researched tuned stainless ones from what I've been able to find out, but BMW's original equipment (Eiberspaech?) is likely the best choice unless you do other mod's e.i. chip, larger throttle body, cam, headers, MAF, intake extrusion honing, etc.

Here's a link which rates a dozen or so brands but does not list specific engines.