Let me clarify what the problem is before we discuss this further: When you start the Turbo in the morning, in the first minute or so, the exhaust is really loud, then after 1 minute, it becomes quiet. The EVOMS in my car sounds somewhere between that first minute of loudness and the eventual calmness. It's really not too loud, but because it is a higher frequency noise and remains a. at idle and b. stays farily loud above 3000 rpm at moderate throttle application (both of these I did not have previously, as the Cargraphic exhaust is actually quiet at idle and above 3000 only loud with aggressive throttle application). In a track or weekend car, with a younger person perhaps, a juvenile delinquent for example, this noise might/would have been ok. In a daily driver, it was causing me to have a headache.

There is also no doubt about the second change: The low rumbling from the Cargraphic exhaust was greatly diminished. The deep gutteral roar that shakes the car, a cross between hostility and anger Smiley, when jabbing on gas pedal at traffic stops to about 1200 rpm, was gone (this I missed dearly). The exhaust note shifts to a more irritating and stressful higher frequency as a result. In fact, I was sitting in the guest area of the shop when they changed the ECU from EVOMS back to my original ECU and then started the car. As soon as they fired up the engine, I instantly recognized the rumbling and knew the old ECU is back.

Most people change exhaust and ECU tune together, so would not be able to hear a change from an ECU tune alone. Partly because of this, IMO the fact that a change is rarely described doesn't mean it doesn't exist, nor do I think that it's restricted to EVOMS. I would agree it might be more severe with EVOMS + Cargraphic + my particular car than other situations. I would also agree that it might be worse with EVOMS because for whatever reason it happens at idle as well and therefore very easily noticeable. 

Of the parameters that are manipulated, boost, timing, AFR, I am speculating that the culprit is the Air Fuel Ratio (runnning rich?). For sure I will ask people more about this. Because an ECU tune by definition changes combustion parameters,  it actually would surprise me if an exhaust sound does NOT change with any particular ECU tune. Well, at least a little bit?

PS: Toby, you seem to have plenty of experience with turbo tuning, you've never noticed anything like this before? A different exhaust sound when combustion parameters of the turbo are changed?


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Regards,
Can
997 Turbo + Bilstein Damptronic ( Review and Pictures ) + ECU Tune ( ??? ) + Cargraphic Exhaust ( Oh heavenly noise! )