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Thread: Supercharger throttle body question

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  1. #1
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    Supercharger throttle body question

    Ok finally got moved and settled into new home so back at putting super charger on my fiero,2.3 quad 4, 749 ecm, code59. It was suggested that i use 2 throttle bodies, one on intake and the other in front of the supercharger. Im setting up the mechanical stuff and am wondering if i need to run a/the iac motor on the TB in front of the supercharger? I have several TB's of different types, one that looks easiest to use is a ford with no iac motor provision with a screw to adjust T-plate. It does have a T-plate bypass port though. Im guessing no aslong as theres enough air coming threw #1 TB??

    Any advice is always greatly appreciated!!
    Last edited by BigBanks78; 02-12-2018 at 12:06 PM. Reason: forgot something

  2. #2
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    What kind of charger

  3. #3
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    Eaton m62 from what I find on the net. was recommended i use a recirc valve between throttle bodys and just wanted to make sure i pick the right TB before i modify it.:-)

  4. #4
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    M62 will have a recirc built in to route air back to the tb side of the charger.just run throttle before the blower and make sure you build the adaptor plate with the recirc hole in it and map sensor hose in the manifold under the blower

  5. #5
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    well maybe its not an m62 because theres no built in recirc valve, It came off a 99 mercedes c230, looks like a flattened A/C compressor clutch and all. I'm not using the clutch, going to make a solid pully for it. Im thinking i can use the screw to crack open the throttle plate if the port bypassing the plate isn't enough for engine to idle but this is my first supercharger installation so not very confident about my thinking.

  6. #6
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    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!
    Last edited by Xnke; 02-14-2018 at 04:57 PM.

  7. #7
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    Yes using the recirc valve for idle and was going to try controlling valve with ecm, only closing after i get past a certain throttle percentage. thought about having valve start to close at maybe 20-30% and fully closed or max programmed boost at 60-70% and above (just estimated numbers) My reasoning is i want the option to be lite on the throttle and get better gas mileage, if at all possible. probly wont make much pressure till a certain rpm anyway but I'm just experimenting. I do have a blow off valve too. And thanks for reminding me about the heat

  8. #8
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    The bypass valve is pneumatic and operates from engine vacuum. It's the same actuator as what came on the GM3800, there's no need to have the PCM control it if it's hooked up properly. The PCM control on the 3800's was used to prevent it from engaging when overtaking on the highway and control surging when used with the cruise control system.

    You only need the one bypass valve, there's no need for a seperate blow-off valve unless you're only running the single throttle downstream of the supercharger.

    Did you ever get your engine running for this project? Your last thread indicated you still had some issues.

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