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it's the 987/cayman that has the long-neck plenum. the 997 is shown in the link to pedro's site below and is quite stubby. i think the 987/cayman have the long neck to distance the throttle body from the resonance flapper on the plenum, there to add more low rpm torque similar to the resonance tube on our cars. the problem with this is that that flapper is an obstacle to airflow at high rpm/airflow situations. it also must mess with the vacuum available, as the 987/cayman aos has two connections at the plenum.
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