Sorry but those plenum reducing plates are worthless. There is no fuel to keep suspended so no issue there, they may help throttle response but those engines have no issues there either, they are very responsive, also with a smaller plenum volume the cylinders will have more effect on each other than when they have a larger volume especially those cylinders breathing from a corner, what are they supposed to do when the cylinder right befor it in the firing order just sucked all the air out of that corner right before it started trying to pull in air? The large plenum reduces that effect, so in my opinion they are a waste and actually counter productive. If you wish to increase the rpm you can cut down the runners some but again you would actually be increasing the plenum it pulls from witch is not a bad thing. A bigger plenun volume helps smooth out the flow through the throttle body making a small throttle body seem just little bigger. That big plenum is not hurting a thing.