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Originally Posted by The Radium King
...finally, looking at that 5500 rpm dip you have. i am trying to get my head around it. truegearhead had something similar. you see it on occasional dyno results. it may be an effect of scaling, as it shows up on the factory dynos also - ie, it just looks worse on a dyno that has an exaggerated 'y' scale. what is happening at 5500 rpm? the resonance tube closes again (opens at 3000 rpm, closes at 5000 rpm) ...
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Good points. That dip could just be a sticking/dirty/slow resonance flapper valve. Slight vacuum leak maybe? Electric valve starting to fail?
From an old Porsche archive:
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"... Below 3,000 rpm, the cylinders draw air from a “short” path. From 3,000 rpm to about 5,100 rpm – when the resonance flap opens – the cylinders draw from a long intake path, which boosts torque. Above 5,100 rpm, the flap again closes to allow the cylinders to draw intake air from a shorter intake path to boost horsepower at higher engine speeds."
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Last edited by 78F350; 04-01-2018 at 09:50 AM.
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