i'll modify my bs slightly. the 987 series have a second resonance flapper on the plenum; the 986 does not. the ipd product does away with this flapper on the 987; it's a non-issue on the 986. so, perhaps no issue with low rpm tuning to add an ipd plenum (or equivalent) to a 986?
here is the thread that i referred to earlier; scroll down a little over 1/2 way to see a quick simulation of airflow through a stock plenum - see how the sharp inside bend reduces airflow by over 50%:
linky
perhaps someone could confirm, however, that max airflow is not required? ie, that the engine recieves sufficient air as designed. i ask as i read somewhere that the 987 has smaller manifold intakes than the 986, so revising airflow pre-manifold on the 986 (with smaller engine) may not be worthwhile?
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