I know this has been asked before, but there must be a way to put an open air dumpvalve on a T7 system. Abbottracing sells a special open air dumpvalve with twin piston (or twin spring, something was twin anyway lol) that keeps it from sucking in air at idle. Most people say that you can't do this with an mass aiflow system car, but even the new Impreza WRX is frequently modified with an open air dumpvalve, and it is a mass/airflow car. (at least the newer US WRX's are, I didn't believe they were but a friend of mine showed me his sensor, small as heck too. lol) I doubt very much that during the shift the computer takes into account the air being dumped, and even if it did, it would just momentaryly run slightly rich. I think the idle problems are mainly that the recirculating valves stick open a little longer. I'm curious if anyone has tried an dumpvalve on a T7 car designed specifically to dump into the atmosphere. It would be cool to get that loud whoosh.
However ... if you're not interested in the sound, despite a number of people's noted reccomendations for atmospheric dumpvalves, I think they have a slight performance disadvantage. Eric with the 900 claimed the air coming out of the intake pipe was 140 degrees, so he didn't want to recirculate that. But that's the temperature of the COMPRESSED air, much as it heats up when compressed (to well above 140 degrees which is why you need an intercooler) it will cool significantly when decompressed. Think about it. If compressing it to 15 psi heats it up to say 200 degrees, decompressing it from 15 psi to atmospheric pressure should take it back down to about ambient temp right? (not accounting for heat created by inneficiencies in the turbo compressor) Now if it's heated to 200 degrees, and then cooled to 140 degrees and THEN decompressed to atmospheric pressure the temperature of the gas coming out should be below ambient temp! The compression and then radiative cooling of the gasses will work in exactly (not counting for evaporation and condensation) the same way as your air condition works. The gas is compressed which makes it hot, then cooled to close to ambient temp through an intercooler (in your a/c's case the condensor) then decompressed and subsequently cooled when released into the atmosphere (in the a/c's case in the evaporator). Your air con may use the heat absorbtion of evaporation and condensation to grab even more heat from the air going into your car, but the intercooled turbo system should do nearly the same thing, though a lot less efficiently. Also recurculating the gasses reduces the amount of air that has to go through the air filter, since some filtered air is wasted when it's dumped. This too gives more power. Atmospheric dumpvalves may have a number of performance disadvantages, but they sure do sound cool and I want one dangit! lol Oh well ..