Brief Info About Lid Spacers and Heat Insulator Plates
There is basically zero difference between the phenolic and billet, as far as overall gains. They do the same thing, but very minimal heat is transferred from the blower case to the lid. The billet ones are easier to drill and tap for foggers/meth nozzles, since the billet can be drilled directly, the phenolic will need brass inserts epoxied in. We make them from 1/2" all the way to 2" if needed, 5/8" being the thinnest we can do to put nozzles in.
The main, and possibly only benefit from the lid spacer alone, is it moves the brick up and away from the blower outlet. Anyone taken off a high mileage lid, and see a triangle shape dirty spot on the brick? There's a reason for that. The brick is so close to the outlet of the rotors, that 95% of the air only goes through that spot on the brick, essentially only using less than 50% of the surface area, both for flow volume and for cooling. The rest of the brick is useless. By raising up the brick, you get more volume through the brick, more cooling efficiency out of the brick, and you will actually see 1-2psi gained at the MAP sensor, since less air is backing up at the rotor outlet. Before you say "but boost is a measure of restriction", yes you are correct. The restriction being your engine flow, which didnt change, but not you are able to push more air into that restriction (the lid plenum volume), so that why the boost numbers will climb. We have seen as much as 35hp on a 650hp car with JUST a lid spacer. Plenum volume goes up a little bit, and it helps the rear cylinders fill a bit better as well with the ZL1 lids.
All the heat from the heads (and remember, that's the hottest part of the engine, besides the pistons themselves), has a direct path to the blower case. With the heat from the heads, and the rotors themselves, its not uncommon for 250* blower case temps. Which one, is bad for rotors, bearings, etc, but also distorts the case and rotors, especially if you thermal shock the rotors with anything sprayed in (like NOS through the TB). By using the phenolic to separate the heads, you make a air gap between the valley and blower case, as well as kill the thermal path between the heads and blower. I have had customers go do a 1/4 mile, come back, blower is crazy hot to touch, add the heat plates, and next time they went out the blower was barely warm. Another thing to keep in mind here, is that the entire blower is surrounded by 300* or warmer air, since the headers will make a ton of residual heat, and the ZL1 lid especially, will just soak up all that heat (not really sure what GM was thinking with that one, it acts like a reverse heatsink). So not only does your IC have to cool ALLLL the heat that has soaked into it through direct contact, but also all the heat absorbed by the rotors thats now in your air charge, as well as whats gonna get warmed up again by the lid surface, so its not very efficient. With the head plates, the only real thing the IC has to cool is the air charge itself. As a final piece of data, look where your IAT sensor is. Its in the lid. The air still has to pass through the blower case to get into the heads. If the blower case is 200*, by the time its passed the IAT, its going to pick up 10-20* or more, that that IAT isnt even going to see......so keep that in mind.
The head plates are made in 1/4" (for the low clearance and ZR1 guys mainly), 1/2" and 1". They come in cathedral, adapter, and square ports, both stock size and .050" ported oversize (based off an SPS Haymaker port size). We can also add the NOS or Meth nozzles to the 1" ones, under the blower.
If you read all that, I appreciate your time, and let me know if you guys have questions.