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Geoff
01-05-1999, 10:27 PM
Has anyone made any exhaust/cat mod's to their M3/3.2/SMG and what performance impact was there ?<p>I suspect that there is too much back pressure in my exhaust system and as a result my mid-range power is down significantly. Recent dyno has confirmed this.

Rainman
01-11-1999, 09:41 AM
<i>: Has anyone made any exhaust/cat mod's to their M3/3.2/SMG and what performance impact was there ?<p>: I suspect that there is too much back pressure in my exhaust system and as a result my mid-range power is down significantly. Recent dyno has confirmed this.<p></i><br>Hi<br>Depends who you talk to !<br>Mine is the R.S.A. 3.2 98 model , and I noticed the same symptom . Here in South Africa our unleaded fuel at altitude (Johannesburg) is only<br>91 . Our leaded is 93 and has a more reliable rating . Hence our compression ratio is dropped to 10.5:1 from the german spec 11.3 odd .<br>I find this very difficult to stomach and was quite dissapointed in the cars performance .<p>The point here was to convert to leaded fuel so I trashed the cats and fitted free-flow box in its place , the rest of the pipe is standard . Next<br>they changed a resistor on the fuel injection system , balanced the throttle bodies and modified the airbox - what I see is a huge pipe <br>in front on the left kidney grill .<p>The problem was solved !<br>But : since then I have done some futher phoning<br>around and see that Schnitzer only makes a rear <br>silencer ! And performance increases are minimal!<br>So if they don't think it restrictive neither do<br>I .<br>PART II :<br>It seems the trick with these cars is too leave them standard and consentrate on remapping the <br>fuel / vanos chips . My car is booked in for a <br>"tune-up" on Monday , and I am putting my cats<br>back-on before so we will see what the dyno sais.<br>This guy has the bmw software for the chips and remaps the existing chips - undetectable - no motorplan problems .<p>Apparently the real performance gains come from<br>vanos tuning , with further enhancements by adjusting a cam securing bolt under the tapett cover !<br>Wish you well , don't get down there's a solution out there , if I find it first I'll let you know.


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