I recently converted my 98' 323is to M3 exhaust with an aftermarket stainless cat back. The car runs and sounds good with the exception of it making a popping sound under deceleration. Its not terribly loud but its just not the way a BMW should sound like to me. It makes me think of a Honda Civic some high school kid has that got an Auto Zone gift certificate and decked it out with a bunch of crap. I would like to get a quality intake as well but am afraid it will put the car out of tune more than it already is. I have never messed with programing before n or chips. Would a chip be my solution or am I just stuck with the sound?
My car does the same thing, Its not all that noticable or loud, but i do hear it under the same conditions as you do. My resolution may have been unique, It turned out I had a restricted exhaust, the cat was shot all to hell and back, and the pipes, (down pipes going to the cat, and the pipes from the cat to where the ACS exhaust pipes start) looked as if a person who knew nothing about exhaust put it on, there was 3 diffrernt size pipes from 2.5 inch down to 1.5, they welded in the gaps between pipes so they fit- very restricted exhaust, had all that crap replaced, I do not think that the popping sound is a bad thing, i still get it when I am (for example) cruzing at 3500 rpms, I take my foot off of the gas pedal and let the car slow down while still in gear, the popping occurs right when i take my foot off of the pedal-
i stress over strange sounds from my ride too,
__________________ 1993 e36 325is
AC Schnitzer Exhaust
AC Schnitzer type I full body kit
AC Schnitzer chip
A monkey in the trunk (stock)
It sounds like you have back fire. Probably with the new exhaust the ignition timing had been retarded. Adding a chip would most likely solve the problem as the ignition timing would be advanced. Race car's use back fire as a way to bump or keep RPM's higher while off the throttle.
Back pressure is something else. It's used as an airflow restriction in the exhaust system to increase low RPM torque, usually at the expense of some high end horse power. An angled peice of metal which diverts airflow inside the muffer would cause a build-up in back pressure as compared to a straight through less restrictive muffler which would produce more high end horse power at the expense of low end torque. This has nothing to do with the "popping" sound. Backfire is unburnt fuel being shot out the exhaust pipe (result of retarding the ignition timing).
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Yeah it's a backfire because of the timing when you're letting off the gas, and ussually at a higher rpm. It is affected by backpressure however, ussually when you go to a free flowing exaust with stock software you get the popping because timing is all out of wack for how little back pressure is in the system.
Hope that made sence
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