Type: Plenum Spacer
Models: Only one available. 5/8" Thermal Polymer.
Pros: When installing the spacer, I found that my plenum was very dirty, so my wife cleaned that while I installed the spacer. The combination of the spacer and cleaning resulted in a much cleaner throttle response with better power. I probably should have reset my ECU for comparison purposes, but I didn't until recently.
Cons: I'm too lazy to reinstall the engine cover
Bought at/Price: Custom Creations (Riverside, CA) $110 out the door (with heavy arguing and negotiation).
Comments: Per my conversation with the tech support, DO NOT apply RTV silicone or any other gasket making substance to the spacer. The thermal polymer will seat itself once it heat cycles. Plus it's somewhat flexible and makes a good seal. Also, because of the flexibility, the holes may not line up with the plenum. Just tweak the spacer a little hear and there before you tighten all of the bolts.
Supposedly this mod for my MY is best coupled with the MREV2 lower plenum which is actually a modified AT lower plenum.