Good product, but have a plan whe you install them w/ EGR.
My experiences with the 8mm phenolic spacers have been centered around using them on a 2005 Subaru Forester X (2.5L SOHC EJ253), and as such may be a little different than others... The spacers themselves are very high quality, and raise the intake manifold off of the engine by 8mm (approximately 5/16th inches). The whole premise is that they should reduce the air temperature of the incoming air by reducing heat entering the intake manifold, which I can say these do indeed reduce the manifold temperature as tested by touch. Things to be aware of though, if your car is equipped with an EGR system you may run into a few problems as I did. The exhaust tube should be lengthed by 8mm, which can be fairly hard to do because if it's not exact you will have a significantly hard time getting the flaired ends to seal properly. I have heard of people not loosening the tube and using a pry bar installing the gaskets via tweaking the tube (with it still installed). I chose to attempt to lengthen the tube via cutting it in half and welding a length of tube over the tops of both, which while in theory should have worked well, resulted in a very annoying exhaust leak because the ridgid tube kept binding. My tempoaray solution was to use two M20-1.5 drain plugs and plug both the intake manifold and cylinder head EGR ports. This will result in a check engine light, slightly decreased fuel economy on the highway and slightly increased engine operating temperatures. An ECU tune could remedy this and/or a custom flexible EGR tube, or both. My observations of performance changes have been that it is very complimentary to a throttle body spacer, and while I have no dyno results, I suspect that a there has been a 1-3hp increase. More importantly though, the power band now seems to move beyond 4,000rpms and seems to have significantly more torque. I have also seen an increase of in-city fuel economy, but as mentioned above a decrease in highway economy (because of the EGR issues). Overall I would recommend this product, but do not expect this to make a world of difference without other moditications, which it will compliment nicely.