I read that without the SAP the first 5-10 minutes of driving will pollute more than the next few hours so clearly it’s a significant part of pollution reduction. It's stupid expensive to get a new one but if you can source a decent used one it's the route I would take.

The bypass for track use makes more sense however. It's quite silly to apply highway emission rules to racing.

Back to the topic: if you get 90 seconds of sound like the car is trying to hover thats the classic symptom of the pump bearing shot.

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)