Quote:
Originally Posted by ray7792
Hello,
I've always wondered if everyone else's brz sounds slightly strange when driving before it is fully warmed up.
I hear a whiny noise when I accelerate, almost like a mini supercharger...most likely source is the belts.
The exhaust note is a lot more raspy and dull sounding compared to the usual deeper note rumble (I have UEL)
But once the car is warmed up, all of these disappear. What is the cause of this?
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The predominant cause of the engine sound and resultant exhaust note prior to the engine reaching operating temperature is negative valve overlap combined with an initial high idle. Simply put, NVO helps warm the primary catalytic converter, lowering tailpipe emissions. See this patent for more information:
http://www.google.com/patents/US6394051