Grimmspeed Thermal Phenolic Spacer 8mm 02+ Subaru Phenolic spacers have been used for years by many other specialized automotive companies, but this is very new technology to the Subaru world. What it does Greatly reduces the transfer of heat from engine to intake manifold thus reducing heat soak. One of a kind true Phenolic material, not cutting board material like others. The cooler your intake temperature is the denser the air is which leads to more power For every 5 degree reduction in air temperature, increases power by 1. The cooler and denser the intake air that the engine sucks in, increases the amount of air that can be mixed with fuel thus increasing efficiency. Direct bolt-on. When running the oem gasket only, your intake manifold gets very hot to the touch, enough to burn your hand. When the oem gasket is replaced with our Phenolic Spacer, your hand can be placed on the intake manifold without any issues. We have installed both with and without OEM Subaru Gaskets and have had no issues with either way. We do recommend using 2 sets of oem gaskets however, one on both sides of the spacer. USA made