It's an M62, the original recirc valve was in the mercedes piping attached to it.
If you're still trying to run the remote-mount air-to-air intercooled thing, you'll need one throttle before the blower, and one throttle on the intake manifold. The recirc valve is to keep the blower from overheating at idle, it's got nothing to do with relieving pressure on the throttle plates, when set up this way.
The reason for the twin throttles is because as the throttled volume goes up, the engine can't pump the throttled volume down quickly enough-and you have *severe* drivability issues. Essentially everything behind the throttle plate becomes your intake plenum volume...more than 2X your engine displacement starts to get really unruly very quickly.
If you were to just bolt the eaton directly to the manifold and not have the extra piping for the intercooler, volume of the intercooler, and the volume of the plenum all adding in, then you would only need the single throttle + compressor bypass valve.
The bypass valve isn't a "blowoff" or "pressure relief" valve in the same way that you use one in a turbocharged application-it's there so that at idle, when the inlet of the supercharger is throttle down to just the idle air opening, the supercharger isn't trying to pump -15 inches of vacuum up to -5 inches of vacuum-which it will absolutely attempt to do, and it will get VERY VERY hot very quickly as it attempts to do this. The rotors will get hot faster than the case, they rub the case, and rapid wear ensues-and after extended idle times you can even swell the rotors enough to lock them in the case. By opening the compressor bypass, the air being moved from the inlet to the outlet of the supercharger does not get compressed at all and only heats up by the friction work being done-not the compression work. Closing the bypass allows the blower to start pressurizing the intake manifold, which causes the air to be heated by the work done to compress it as well as the friction incurred by the slip past the rotors-and at idle speeds, any amount of pressurization will start pushing the slip factor up considerably-adding even more heat to the equation. (rotor speed too low to effectively seal the rotors to the case)
Before someone jumps in and says that i'm full of crap and they only need to bypass valve to vent pressure, thinking that the old 6-71 style blowers don't have one so the Eaton doesn't really need it either, you need to think about how the old Roots style blowers are installed-they are drawing fuel from the carburator above, and thus are vapor cooling the rotor assembly, the case, and the charge air. Even the fuel injected blown setups using those types of blowers inject the fuel above the rotors-for exactly the same reason.
In the case of the eaton, it's design allows for dry running by allowing the rotors to "freewheel" and not do work when doing the work would cause so much waste heat that it would damage the case-these eaton blowers are nicknamed "heaton" blowers for a good reason-They get hot when you ask them to do work!
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