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M2 Technical Topics > S55 Engine / Drivetrain / Exhaust / Bolt-ons / Tuning > Does having the valves always open fix the weed-wacker sound?

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      05-29-2019, 09:33 PM   #1
Blue2
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Does having the valves always open fix the weed-wacker sound?

I always drive my M2C in Sport+ steering and engine with MDM on. I have this setting saved as M1 and turn it on as soon as I start the car. Regardless, if I get on the throttle at all during the first few minutes, it sounds like a weed wacker (or maybe a sick cat).

Is this a function of the valves being closed for a few minutes or is it something else, like the exhaust being cold? I'm considering the BMS OBDII Can Flap Module and wanted to know if this would fix the issue.
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      05-29-2019, 10:34 PM   #2
rjtoudouze
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I warm my car up before hitting my M1 button. I think it sounds great, just too quiet.
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      06-14-2019, 01:30 PM   #3
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99% sure that it's from a cold exhaust.
Same thing happens in efficient mode if the car is off for 30-45 mins. The engine retains some healthy heat but the exhaust had time to cool: You get some raspy sound when you rev up but in efficient you only notice above 4000rpm or if the windows are down.

I actually like the sound as it reminds me of the old E46 rasp... though I recall that everyone else hated that. Maybe I just have bad taste... or maybe I enjoy yard work.
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