Uhhh, Chris... I think you're a bit confused here.
"Closed loop" refers to the control system of the FI, not the vacuum system. It means that the control system has some measurement of its output and uses that signal to modify the gains in the control system. In an engine's case, the FI has an O2 sensor in the tailpipe, and uses the signal from that to tweak the mixture.
The K&N thing has been done. I've seen a 2.0 with a K&N cone directly on top of the throttle body, sticking straight up. An aluminum rain shield sat above it to keep most of the water out of the motor--needed, since there was no room for the rain tray.
Jeff Shyu also had a homemade intake with a K&N filter. He used some PVC pipe to plumb from the throttle body to the filter. I forget if he plumbed the pressure-side vacuum lines into the pipe, or if he had smaller filters that he just stuck on the ends of those lines. Either approach should work with D-jet.
If you have L-jet, then you have to plumb the lines that are in between the air flow meter and the throttle body into something that is in between the air flow meter and the throttle body.
--DD
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Pelican Parts 914 Tech Support
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