Both are about keeping the intake charge cooler. Nominally you get some power increase form the increased runner length moving the power band a little on the IM spacer, but the major issue was just simply keeping things cooler and they made a good difference to be sure.
We did discontinue them though... the manufacturing costs went up a lot and they weren't selling well enough to justify carrying the huge cost in inventory. If someone else is ever interested in selling/producing them I can provide the CAD models for the spacer so they can get them fabbed up. You need to use G10 phenolic to be safe with the engine.
Later!
Steve
