Quote:
Originally Posted by 78F350
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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so, perhaps i am overthinking, but with engine conversions, and with plenum changes, often the resonance tube has to be rotated/moved for clearance; operation may have been impacted? oil can pool in the resonance tube - if positioned other than oem, it may start to not operate properly. or perhaps they get weak over time and can't return properly when faced with 5000 rpm airflows.
the other thing i am thinking is perhaps the turn-over points are not optimal for modified engines - ie, perhaps the flap should close sooner? not close at all? i presume this is not something you can change with a tune, as jfro's result w softronic tune indicates (he's got the dip too):
Dyno results!!
it would be interesting to dyno with the flap always open, and/or always closed, and see what happens with the dip.