The attached pictures show the plenum on N170BR. The composite elements are 3 bid E-glass and 1 bid carbon with the occasional foam and 2 bid carbon stiffener. I used standard Jeffco epoxy which has shown excellent heat resistance.  I made the inlet and intercooler ducts by carving male plug molds in high density foams, coating the plugs in car wax and applying a 2 bid layup. I removed the shells from the molds and then applied another bid of glass followed by one bid of carbon. The carbon makes a dramatic improvement in stiffness.

The large top cover piece was molded using the inside of the cowling. The final weight of the cover was about 1.4 lbs, less than half the weight of the silicone perimeter seal and fasteners that you would use in a conventional installation.

My engine is based on a Lycoming IO540 K series. It has a large capacity oil pump, long plug angle valve cylinder heads and 8.5:1 pistons. It produces its rated 350 HP at  2700 RPM and 35" (dynamometer tested).  You can see another picture of my engine in almost any Trade-a-Plane in the Barrett Performance Aircraft ad.

During climb I fly at Va ~175 KIAS, 29 GPM, 87% power (300 Hp), 1000 FPM average to the mid 200 flight levels. CHT NEVER exceeds 400 degrees F.

In cruise I run 2500 RPM, 28 inHg, 21 GPM (150 ROP), 1500 TIT, 390 CHT (+- 10 degrees).

During races I run at 104% rated (takeoff) power.  I run the engine relatively hard all the time and always at 75% in cruise. At 845 hours TT the engine has the same compression as new (mid 70s).

The big secret in designing an effective plenum is no big secret at all. Make it tight. Seal all cracks, gaps and holes that do not directly cool the engine.  Remember that there will be nearly 1 PSI deforming the plenum in flight. Many gaps enlarge under pressure, bleeding off precious cooling air just when you need it.  Remember that  silicone perimeter sealing "belting" is not very effective, especially at the corners, and all those little gaps add up.

Regards
Brent Regan